Changeset 391 for python/trunk/Python/pystrtod.c

Timestamp:

Mar 19, 2014, 11:31:01 PM (11 years ago)

Author:

dmik

Message:

python: Merge vendor 2.7.6 to trunk.

Location:

python/trunk

Files:

• . (modified) (1 prop)
• Python/pystrtod.c (modified) (8 diffs)

python/trunk/Python/pystrtod.c

@@ -7 +7 @@
 #endif
 
-
-/* ascii character tests (as opposed to locale tests) */
-#define ISSPACE(c)  ((c) == ' ' || (c) == '\f' || (c) == '\n' || \
-                     (c) == '\r' || (c) == '\t' || (c) == '\v')
-#define ISDIGIT(c)  ((c) >= '0' && (c) <= '9')
-
+/* Case-insensitive string match used for nan and inf detection; t should be
+   lower-case.  Returns 1 for a successful match, 0 otherwise. */
+
+static int
+case_insensitive_match(const char *s, const char *t)
+{
+    while(*t && Py_TOLOWER(*s) == *t) {
+        s++;
+        t++;
+    }
+    return *t ? 0 : 1;
+}
+
+/* _Py_parse_inf_or_nan: Attempt to parse a string of the form "nan", "inf" or
+   "infinity", with an optional leading sign of "+" or "-".  On success,
+   return the NaN or Infinity as a double and set *endptr to point just beyond
+   the successfully parsed portion of the string.  On failure, return -1.0 and
+   set *endptr to point to the start of the string. */
+
+double
+_Py_parse_inf_or_nan(const char *p, char **endptr)
+{
+    double retval;
+    const char *s;
+    int negate = 0;
+
+    s = p;
+    if (*s == '-') {
+        negate = 1;
+        s++;
+    }
+    else if (*s == '+') {
+        s++;
+    }
+    if (case_insensitive_match(s, "inf")) {
+        s += 3;
+        if (case_insensitive_match(s, "inity"))
+            s += 5;
+        retval = negate ? -Py_HUGE_VAL : Py_HUGE_VAL;
+    }
+#ifdef Py_NAN
+    else if (case_insensitive_match(s, "nan")) {
+        s += 3;
+        retval = negate ? -Py_NAN : Py_NAN;
+    }
+#endif
+    else {
+        s = p;
+        retval = -1.0;
+    }
+    *endptr = (char *)s;
+    return retval;
+}
 
 /**
@@ -19 +66 @@
  * @endptr:  if non-%NULL, it returns the character after
  *           the last character used in the conversion.
- * 
+ *
  * Converts a string to a #gdouble value.
  * This function behaves like the standard strtod() function
@@ -36 +83 @@
  * zero is returned and %ERANGE is stored in %errno.
  * If memory allocation fails, %ENOMEM is stored in %errno.
- * 
+ *
  * This function resets %errno before calling strtod() so that
  * you can reliably detect overflow and underflow.
@@ -42 +89 @@
  * Return value: the #gdouble value.
  **/
+
+#ifndef PY_NO_SHORT_FLOAT_REPR
+
+double
+_PyOS_ascii_strtod(const char *nptr, char **endptr)
+{
+    double result;
+    _Py_SET_53BIT_PRECISION_HEADER;
+
+#ifdef __OS2__
+    /* @todo: Quick hack: disable FPU exceptions to avoid unexpected
+       SIGFPE. The proper way is to fix compiler runtime so that its
+       exception handler undoes FPU CW reset caused by bogus OS/2 DLLs. */
+    _control87(MCW_EM, MCW_EM);
+#endif
+
+    assert(nptr != NULL);
+    /* Set errno to zero, so that we can distinguish zero results
+       and underflows */
+    errno = 0;
+
+    _Py_SET_53BIT_PRECISION_START;
+    result = _Py_dg_strtod(nptr, endptr);
+    _Py_SET_53BIT_PRECISION_END;
+
+    if (*endptr == nptr)
+        /* string might represent an inf or nan */
+        result = _Py_parse_inf_or_nan(nptr, endptr);
+
+    return result;
+
+}
+
+#else
+
+/*
+   Use system strtod;  since strtod is locale aware, we may
+   have to first fix the decimal separator.
+
+   Note that unlike _Py_dg_strtod, the system strtod may not always give
+   correctly rounded results.
+*/
+
+double
+_PyOS_ascii_strtod(const char *nptr, char **endptr)
+{
+    char *fail_pos;
+    double val = -1.0;
+    struct lconv *locale_data;
+    const char *decimal_point;
+    size_t decimal_point_len;
+    const char *p, *decimal_point_pos;
+    const char *end = NULL; /* Silence gcc */
+    const char *digits_pos = NULL;
+    int negate = 0;
+
+#ifdef __OS2__
+    /* @todo: Quick hack: disable FPU exceptions to avoid unexpected
+       SIGFPE. The proper way is to fix compiler runtime so that its
+       exception handler undoes FPU CW reset caused by bogus OS/2 DLLs. */
+    _control87(MCW_EM, MCW_EM);
+#endif
+
+    assert(nptr != NULL);
+
+    fail_pos = NULL;
+
+    locale_data = localeconv();
+    decimal_point = locale_data->decimal_point;
+    decimal_point_len = strlen(decimal_point);
+
+    assert(decimal_point_len != 0);
+
+    decimal_point_pos = NULL;
+
+    /* Parse infinities and nans */
+    val = _Py_parse_inf_or_nan(nptr, endptr);
+    if (*endptr != nptr)
+        return val;
+
+    /* Set errno to zero, so that we can distinguish zero results
+       and underflows */
+    errno = 0;
+
+    /* We process the optional sign manually, then pass the remainder to
+       the system strtod.  This ensures that the result of an underflow
+       has the correct sign. (bug #1725)  */
+    p = nptr;
+    /* Process leading sign, if present */
+    if (*p == '-') {
+        negate = 1;
+        p++;
+    }
+    else if (*p == '+') {
+        p++;
+    }
+
+    /* Some platform strtods accept hex floats; Python shouldn't (at the
+       moment), so we check explicitly for strings starting with '0x'. */
+    if (*p == '0' && (*(p+1) == 'x' || *(p+1) == 'X'))
+        goto invalid_string;
+
+    /* Check that what's left begins with a digit or decimal point */
+    if (!Py_ISDIGIT(*p) && *p != '.')
+        goto invalid_string;
+
+    digits_pos = p;
+    if (decimal_point[0] != '.' ||
+        decimal_point[1] != 0)
+    {
+        /* Look for a '.' in the input; if present, it'll need to be
+           swapped for the current locale's decimal point before we
+           call strtod.  On the other hand, if we find the current
+           locale's decimal point then the input is invalid. */
+        while (Py_ISDIGIT(*p))
+            p++;
+
+        if (*p == '.')
+        {
+            decimal_point_pos = p++;
+
+            /* locate end of number */
+            while (Py_ISDIGIT(*p))
+                p++;
+
+            if (*p == 'e' || *p == 'E')
+                p++;
+            if (*p == '+' || *p == '-')
+                p++;
+            while (Py_ISDIGIT(*p))
+                p++;
+            end = p;
+        }
+        else if (strncmp(p, decimal_point, decimal_point_len) == 0)
+            /* Python bug #1417699 */
+            goto invalid_string;
+        /* For the other cases, we need not convert the decimal
+           point */
+    }
+
+    if (decimal_point_pos) {
+        char *copy, *c;
+        /* Create a copy of the input, with the '.' converted to the
+           locale-specific decimal point */
+        copy = (char *)PyMem_MALLOC(end - digits_pos +
+                                    1 + decimal_point_len);
+        if (copy == NULL) {
+            *endptr = (char *)nptr;
+            errno = ENOMEM;
+            return val;
+        }
+
+        c = copy;
+        memcpy(c, digits_pos, decimal_point_pos - digits_pos);
+        c += decimal_point_pos - digits_pos;
+        memcpy(c, decimal_point, decimal_point_len);
+        c += decimal_point_len;
+        memcpy(c, decimal_point_pos + 1,
+               end - (decimal_point_pos + 1));
+        c += end - (decimal_point_pos + 1);
+        *c = 0;
+
+        val = strtod(copy, &fail_pos);
+
+        if (fail_pos)
+        {
+            if (fail_pos > decimal_point_pos)
+                fail_pos = (char *)digits_pos +
+                    (fail_pos - copy) -
+                    (decimal_point_len - 1);
+            else
+                fail_pos = (char *)digits_pos +
+                    (fail_pos - copy);
+        }
+
+        PyMem_FREE(copy);
+
+    }
+    else {
+        val = strtod(digits_pos, &fail_pos);
+    }
+
+    if (fail_pos == digits_pos)
+        goto invalid_string;
+
+    if (negate && fail_pos != nptr)
+        val = -val;
+    *endptr = fail_pos;
+
+    return val;
+
+  invalid_string:
+    *endptr = (char*)nptr;
+    errno = EINVAL;
+    return -1.0;
+}
+
+#endif
+
+/* PyOS_ascii_strtod is DEPRECATED in Python 2.7 and 3.1 */
+
 double
 PyOS_ascii_strtod(const char *nptr, char **endptr)
 {
-#ifdef __EMX__
-_control87(MCW_EM, MCW_EM);
-#endif
-        char *fail_pos;
-        double val = -1.0;
-        struct lconv *locale_data;
-        const char *decimal_point;
-        size_t decimal_point_len;
-        const char *p, *decimal_point_pos;
-        const char *end = NULL; /* Silence gcc */
-        const char *digits_pos = NULL;
-        int negate = 0;
-
-        assert(nptr != NULL);
-
-        fail_pos = NULL;
-
-        locale_data = localeconv();
-        decimal_point = locale_data->decimal_point;
-        decimal_point_len = strlen(decimal_point);
-
-        assert(decimal_point_len != 0);
-
-        decimal_point_pos = NULL;
-
-        /* We process any leading whitespace and the optional sign manually,
-           then pass the remainder to the system strtod.  This ensures that
-           the result of an underflow has the correct sign. (bug #1725)  */
-
-        p = nptr;
-        /* Skip leading space */
-        while (ISSPACE(*p))
-                p++;
-
-        /* Process leading sign, if present */
-        if (*p == '-') {
-                negate = 1;
-                p++;
-        } else if (*p == '+') {
-                p++;
-        }
-
-        /* What's left should begin with a digit, a decimal point, or one of
-           the letters i, I, n, N. It should not begin with 0x or 0X */
-        if ((!ISDIGIT(*p) &&
-             *p != '.' && *p != 'i' && *p != 'I' && *p != 'n' && *p != 'N')
-            ||
-            (*p == '0' && (p[1] == 'x' || p[1] == 'X')))
-        {
-                if (endptr)
-                        *endptr = (char*)nptr;
-                errno = EINVAL;
-                return val;
-        }
-        digits_pos = p;
-
-        if (decimal_point[0] != '.' || 
-            decimal_point[1] != 0)
-        {
-                while (ISDIGIT(*p))
-                        p++;
-
-                if (*p == '.')
-                {
-                        decimal_point_pos = p++;
-
-                        while (ISDIGIT(*p))
-                                p++;
-
-                        if (*p == 'e' || *p == 'E')
-                                p++;
-                        if (*p == '+' || *p == '-')
-                                p++;
-                        while (ISDIGIT(*p))
-                                p++;
-                        end = p;
-                }
-                else if (strncmp(p, decimal_point, decimal_point_len) == 0)
-                {
-                        /* Python bug #1417699 */
-                        if (endptr)
-                                *endptr = (char*)nptr;
-                        errno = EINVAL;
-                        return val;
-                }
-                /* For the other cases, we need not convert the decimal
-                   point */
-        }
-
-        /* Set errno to zero, so that we can distinguish zero results
-           and underflows */
-        errno = 0;
-
-        if (decimal_point_pos)
-        {
-                char *copy, *c;
-
-                /* We need to convert the '.' to the locale specific decimal
-                   point */
-                copy = (char *)PyMem_MALLOC(end - digits_pos +
-                                            1 + decimal_point_len);
-                if (copy == NULL) {
-                        if (endptr)
-                                *endptr = (char *)nptr;
-                        errno = ENOMEM;
-                        return val;
-                }
-
-                c = copy;
-                memcpy(c, digits_pos, decimal_point_pos - digits_pos);
-                c += decimal_point_pos - digits_pos;
-                memcpy(c, decimal_point, decimal_point_len);
-                c += decimal_point_len;
-                memcpy(c, decimal_point_pos + 1,
-                       end - (decimal_point_pos + 1));
-                c += end - (decimal_point_pos + 1);
-                *c = 0;
-
-                val = strtod(copy, &fail_pos);
-
-                if (fail_pos)
-                {
-                        if (fail_pos > decimal_point_pos)
-                                fail_pos = (char *)digits_pos +
-                                        (fail_pos - copy) -
-                                        (decimal_point_len - 1);
-                        else
-                                fail_pos = (char *)digits_pos +
-                                        (fail_pos - copy);
-                }
-
-                PyMem_FREE(copy);
-
-        }
-        else {
-//sigfpe here
-                val = strtod(digits_pos, &fail_pos);
-        }
-
-        if (fail_pos == digits_pos)
-                fail_pos = (char *)nptr;
-
-        if (negate && fail_pos != nptr)
-                val = -val;
-
-        if (endptr)
-                *endptr = fail_pos;
-
-        return val;
+    char *fail_pos;
+    const char *p;
+    double x;
+
+    if (PyErr_WarnEx(PyExc_DeprecationWarning,
+                     "PyOS_ascii_strtod and PyOS_ascii_atof are "
+                     "deprecated.  Use PyOS_string_to_double "
+                     "instead.", 1) < 0)
+        return -1.0;
+
+    /* _PyOS_ascii_strtod already does everything that we want,
+       except that it doesn't parse leading whitespace */
+    p = nptr;
+    while (Py_ISSPACE(*p))
+        p++;
+    x = _PyOS_ascii_strtod(p, &fail_pos);
+    if (fail_pos == p)
+        fail_pos = (char *)nptr;
+    if (endptr)
+        *endptr = (char *)fail_pos;
+    return x;
+}
+
+/* PyOS_ascii_strtod is DEPRECATED in Python 2.7 and 3.1 */
+
+double
+PyOS_ascii_atof(const char *nptr)
+{
+    return PyOS_ascii_strtod(nptr, NULL);
+}
+
+/* PyOS_string_to_double is the recommended replacement for the deprecated
+   PyOS_ascii_strtod and PyOS_ascii_atof functions.  It converts a
+   null-terminated byte string s (interpreted as a string of ASCII characters)
+   to a float.  The string should not have leading or trailing whitespace (in
+   contrast, PyOS_ascii_strtod allows leading whitespace but not trailing
+   whitespace).  The conversion is independent of the current locale.
+
+   If endptr is NULL, try to convert the whole string.  Raise ValueError and
+   return -1.0 if the string is not a valid representation of a floating-point
+   number.
+
+   If endptr is non-NULL, try to convert as much of the string as possible.
+   If no initial segment of the string is the valid representation of a
+   floating-point number then *endptr is set to point to the beginning of the
+   string, -1.0 is returned and again ValueError is raised.
+
+   On overflow (e.g., when trying to convert '1e500' on an IEEE 754 machine),
+   if overflow_exception is NULL then +-Py_HUGE_VAL is returned, and no Python
+   exception is raised.  Otherwise, overflow_exception should point to a
+   a Python exception, this exception will be raised, -1.0 will be returned,
+   and *endptr will point just past the end of the converted value.
+
+   If any other failure occurs (for example lack of memory), -1.0 is returned
+   and the appropriate Python exception will have been set.
+*/
+
+double
+PyOS_string_to_double(const char *s,
+                      char **endptr,
+                      PyObject *overflow_exception)
+{
+    double x, result=-1.0;
+    char *fail_pos;
+
+    errno = 0;
+    PyFPE_START_PROTECT("PyOS_string_to_double", return -1.0)
+    x = _PyOS_ascii_strtod(s, &fail_pos);
+    PyFPE_END_PROTECT(x)
+
+    if (errno == ENOMEM) {
+        PyErr_NoMemory();
+        fail_pos = (char *)s;
+    }
+    else if (!endptr && (fail_pos == s || *fail_pos != '\0'))
+        PyErr_Format(PyExc_ValueError,
+                      "could not convert string to float: "
+                      "%.200s", s);
+    else if (fail_pos == s)
+        PyErr_Format(PyExc_ValueError,
+                      "could not convert string to float: "
+                      "%.200s", s);
+    else if (errno == ERANGE && fabs(x) >= 1.0 && overflow_exception)
+        PyErr_Format(overflow_exception,
+                      "value too large to convert to float: "
+                      "%.200s", s);
+    else
+        result = x;
+
+    if (endptr != NULL)
+        *endptr = fail_pos;
+    return result;
 }
 
@@ -202 +393 @@
 change_decimal_from_locale_to_dot(char* buffer)
 {
-        struct lconv *locale_data = localeconv();
-        const char *decimal_point = locale_data->decimal_point;
-
-        if (decimal_point[0] != '.' || decimal_point[1] != 0) {
-                size_t decimal_point_len = strlen(decimal_point);
-
-                if (*buffer == '+' || *buffer == '-')
-                        buffer++;
-                while (isdigit(Py_CHARMASK(*buffer)))
-                        buffer++;
-                if (strncmp(buffer, decimal_point, decimal_point_len) == 0) {
-                        *buffer = '.';
-                        buffer++;
-                        if (decimal_point_len > 1) {
-                                /* buffer needs to get smaller */
-                                size_t rest_len = strlen(buffer +
-                                                     (decimal_point_len - 1));
-                                memmove(buffer,
-                                        buffer + (decimal_point_len - 1),
-                                        rest_len);
-                                buffer[rest_len] = 0;
-                        }
-                }
-        }
+    struct lconv *locale_data = localeconv();
+    const char *decimal_point = locale_data->decimal_point;
+
+    if (decimal_point[0] != '.' || decimal_point[1] != 0) {
+        size_t decimal_point_len = strlen(decimal_point);
+
+        if (*buffer == '+' || *buffer == '-')
+            buffer++;
+        while (Py_ISDIGIT(*buffer))
+            buffer++;
+        if (strncmp(buffer, decimal_point, decimal_point_len) == 0) {
+            *buffer = '.';
+            buffer++;
+            if (decimal_point_len > 1) {
+                /* buffer needs to get smaller */
+                size_t rest_len = strlen(buffer +
+                                     (decimal_point_len - 1));
+                memmove(buffer,
+                    buffer + (decimal_point_len - 1),
+                    rest_len);
+                buffer[rest_len] = 0;
+            }
+        }
+    }
 }
 
@@ -240 +431 @@
 ensure_minimum_exponent_length(char* buffer, size_t buf_size)
 {
-        char *p = strpbrk(buffer, "eE");
-        if (p && (*(p + 1) == '-' || *(p + 1) == '+')) {
-                char *start = p + 2;
-                int exponent_digit_cnt = 0;
-                int leading_zero_cnt = 0;
-                int in_leading_zeros = 1;
-                int significant_digit_cnt;
-
-                /* Skip over the exponent and the sign. */
-                p += 2;
-
-                /* Find the end of the exponent, keeping track of leading
-                   zeros. */
-                while (*p && isdigit(Py_CHARMASK(*p))) {
-                        if (in_leading_zeros && *p == '0')
-                                ++leading_zero_cnt;
-                        if (*p != '0')
-                                in_leading_zeros = 0;
-                        ++p;
-                        ++exponent_digit_cnt;
-                }
-
-                significant_digit_cnt = exponent_digit_cnt - leading_zero_cnt;
-                if (exponent_digit_cnt == MIN_EXPONENT_DIGITS) {
-                        /* If there are 2 exactly digits, we're done,
-                           regardless of what they contain */
-                }
-                else if (exponent_digit_cnt > MIN_EXPONENT_DIGITS) {
-                        int extra_zeros_cnt;
-
-                        /* There are more than 2 digits in the exponent.  See
-                           if we can delete some of the leading zeros */
-                        if (significant_digit_cnt < MIN_EXPONENT_DIGITS)
-                                significant_digit_cnt = MIN_EXPONENT_DIGITS;
-                        extra_zeros_cnt = exponent_digit_cnt -
-                                significant_digit_cnt;
-
-                        /* Delete extra_zeros_cnt worth of characters from the
-                           front of the exponent */
-                        assert(extra_zeros_cnt >= 0);
-
-                        /* Add one to significant_digit_cnt to copy the
-                           trailing 0 byte, thus setting the length */
-                        memmove(start,
-                                start + extra_zeros_cnt,
-                                significant_digit_cnt + 1);
-                }
-                else {
-                        /* If there are fewer than 2 digits, add zeros
-                           until there are 2, if there's enough room */
-                        int zeros = MIN_EXPONENT_DIGITS - exponent_digit_cnt;
-                        if (start + zeros + exponent_digit_cnt + 1
-                              < buffer + buf_size) {
-                                memmove(start + zeros, start,
-                                        exponent_digit_cnt + 1);
-                                memset(start, '0', zeros);
-                        }
-                }
-        }
-}
-
-/* Ensure that buffer has a decimal point in it.  The decimal point
-   will not be in the current locale, it will always be '.' */
+    char *p = strpbrk(buffer, "eE");
+    if (p && (*(p + 1) == '-' || *(p + 1) == '+')) {
+        char *start = p + 2;
+        int exponent_digit_cnt = 0;
+        int leading_zero_cnt = 0;
+        int in_leading_zeros = 1;
+        int significant_digit_cnt;
+
+        /* Skip over the exponent and the sign. */
+        p += 2;
+
+        /* Find the end of the exponent, keeping track of leading
+           zeros. */
+        while (*p && Py_ISDIGIT(*p)) {
+            if (in_leading_zeros && *p == '0')
+                ++leading_zero_cnt;
+            if (*p != '0')
+                in_leading_zeros = 0;
+            ++p;
+            ++exponent_digit_cnt;
+        }
+
+        significant_digit_cnt = exponent_digit_cnt - leading_zero_cnt;
+        if (exponent_digit_cnt == MIN_EXPONENT_DIGITS) {
+            /* If there are 2 exactly digits, we're done,
+               regardless of what they contain */
+        }
+        else if (exponent_digit_cnt > MIN_EXPONENT_DIGITS) {
+            int extra_zeros_cnt;
+
+            /* There are more than 2 digits in the exponent.  See
+               if we can delete some of the leading zeros */
+            if (significant_digit_cnt < MIN_EXPONENT_DIGITS)
+                significant_digit_cnt = MIN_EXPONENT_DIGITS;
+            extra_zeros_cnt = exponent_digit_cnt -
+                significant_digit_cnt;
+
+            /* Delete extra_zeros_cnt worth of characters from the
+               front of the exponent */
+            assert(extra_zeros_cnt >= 0);
+
+            /* Add one to significant_digit_cnt to copy the
+               trailing 0 byte, thus setting the length */
+            memmove(start,
+                start + extra_zeros_cnt,
+                significant_digit_cnt + 1);
+        }
+        else {
+            /* If there are fewer than 2 digits, add zeros
+               until there are 2, if there's enough room */
+            int zeros = MIN_EXPONENT_DIGITS - exponent_digit_cnt;
+            if (start + zeros + exponent_digit_cnt + 1
+                  < buffer + buf_size) {
+                memmove(start + zeros, start,
+                    exponent_digit_cnt + 1);
+                memset(start, '0', zeros);
+            }
+        }
+    }
+}
+
+/* Remove trailing zeros after the decimal point from a numeric string; also
+   remove the decimal point if all digits following it are zero.  The numeric
+   string must end in '\0', and should not have any leading or trailing
+   whitespace.  Assumes that the decimal point is '.'. */
 Py_LOCAL_INLINE(void)
-ensure_decimal_point(char* buffer, size_t buf_size)
-{
-        int insert_count = 0;
-        char* chars_to_insert;
-
-        /* search for the first non-digit character */
-        char *p = buffer;
-        if (*p == '-' || *p == '+')
-                /* Skip leading sign, if present.  I think this could only
-                   ever be '-', but it can't hurt to check for both. */
-                ++p;
-        while (*p && isdigit(Py_CHARMASK(*p)))
-                ++p;
-
-        if (*p == '.') {
-                if (isdigit(Py_CHARMASK(*(p+1)))) {
-                        /* Nothing to do, we already have a decimal
-                           point and a digit after it */
-                }
-                else {
-                        /* We have a decimal point, but no following
-                           digit.  Insert a zero after the decimal. */
-                        ++p;
-                        chars_to_insert = "0";
-                        insert_count = 1;
-                }
-        }
-        else {
-                chars_to_insert = ".0";
-                insert_count = 2;
-        }
-        if (insert_count) {
-                size_t buf_len = strlen(buffer);
-                if (buf_len + insert_count + 1 >= buf_size) {
-                        /* If there is not enough room in the buffer
-                           for the additional text, just skip it.  It's
-                           not worth generating an error over. */
-                }
-                else {
-                        memmove(p + insert_count, p,
-                                buffer + strlen(buffer) - p + 1);
-                        memcpy(p, chars_to_insert, insert_count);
-                }
-        }
-}
-
-/* Add the locale specific grouping characters to buffer.  Note
-   that any decimal point (if it's present) in buffer is already
-   locale-specific.  Return 0 on error, else 1. */
-Py_LOCAL_INLINE(int)
-add_thousands_grouping(char* buffer, size_t buf_size)
-{
-        Py_ssize_t len = strlen(buffer);
-        struct lconv *locale_data = localeconv();
-        const char *decimal_point = locale_data->decimal_point;
-
-        /* Find the decimal point, if any.  We're only concerned
-           about the characters to the left of the decimal when
-           adding grouping. */
-        char *p = strstr(buffer, decimal_point);
-        if (!p) {
-                /* No decimal, use the entire string. */
-
-                /* If any exponent, adjust p. */
-                p = strpbrk(buffer, "eE");
-                if (!p)
-                        /* No exponent and no decimal.  Use the entire
-                           string. */
-                        p = buffer + len;
-        }
-        /* At this point, p points just past the right-most character we
-           want to format.  We need to add the grouping string for the
-           characters between buffer and p. */
-        return _PyString_InsertThousandsGrouping(buffer, len, p-buffer,
-                                                 buf_size, NULL, 1);
+remove_trailing_zeros(char *buffer)
+{
+    char *old_fraction_end, *new_fraction_end, *end, *p;
+
+    p = buffer;
+    if (*p == '-' || *p == '+')
+        /* Skip leading sign, if present */
+        ++p;
+    while (Py_ISDIGIT(*p))
+        ++p;
+
+    /* if there's no decimal point there's nothing to do */
+    if (*p++ != '.')
+        return;
+
+    /* scan any digits after the point */
+    while (Py_ISDIGIT(*p))
+        ++p;
+    old_fraction_end = p;
+
+    /* scan up to ending '\0' */
+    while (*p != '\0')
+        p++;
+    /* +1 to make sure that we move the null byte as well */
+    end = p+1;
+
+    /* scan back from fraction_end, looking for removable zeros */
+    p = old_fraction_end;
+    while (*(p-1) == '0')
+        --p;
+    /* and remove point if we've got that far */
+    if (*(p-1) == '.')
+        --p;
+    new_fraction_end = p;
+
+    memmove(new_fraction_end, old_fraction_end, end-old_fraction_end);
+}
+
+/* Ensure that buffer has a decimal point in it.  The decimal point will not
+   be in the current locale, it will always be '.'. Don't add a decimal point
+   if an exponent is present.  Also, convert to exponential notation where
+   adding a '.0' would produce too many significant digits (see issue 5864).
+
+   Returns a pointer to the fixed buffer, or NULL on failure.
+*/
+Py_LOCAL_INLINE(char *)
+ensure_decimal_point(char* buffer, size_t buf_size, int precision)
+{
+    int digit_count, insert_count = 0, convert_to_exp = 0;
+    char *chars_to_insert, *digits_start;
+
+    /* search for the first non-digit character */
+    char *p = buffer;
+    if (*p == '-' || *p == '+')
+        /* Skip leading sign, if present.  I think this could only
+           ever be '-', but it can't hurt to check for both. */
+        ++p;
+    digits_start = p;
+    while (*p && Py_ISDIGIT(*p))
+        ++p;
+    digit_count = Py_SAFE_DOWNCAST(p - digits_start, Py_ssize_t, int);
+
+    if (*p == '.') {
+        if (Py_ISDIGIT(*(p+1))) {
+            /* Nothing to do, we already have a decimal
+               point and a digit after it */
+        }
+        else {
+            /* We have a decimal point, but no following
+               digit.  Insert a zero after the decimal. */
+            /* can't ever get here via PyOS_double_to_string */
+            assert(precision == -1);
+            ++p;
+            chars_to_insert = "0";
+            insert_count = 1;
+        }
+    }
+    else if (!(*p == 'e' || *p == 'E')) {
+        /* Don't add ".0" if we have an exponent. */
+        if (digit_count == precision) {
+            /* issue 5864: don't add a trailing .0 in the case
+               where the '%g'-formatted result already has as many
+               significant digits as were requested.  Switch to
+               exponential notation instead. */
+            convert_to_exp = 1;
+            /* no exponent, no point, and we shouldn't land here
+               for infs and nans, so we must be at the end of the
+               string. */
+            assert(*p == '\0');
+        }
+        else {
+            assert(precision == -1 || digit_count < precision);
+            chars_to_insert = ".0";
+            insert_count = 2;
+        }
+    }
+    if (insert_count) {
+        size_t buf_len = strlen(buffer);
+        if (buf_len + insert_count + 1 >= buf_size) {
+            /* If there is not enough room in the buffer
+               for the additional text, just skip it.  It's
+               not worth generating an error over. */
+        }
+        else {
+            memmove(p + insert_count, p,
+                buffer + strlen(buffer) - p + 1);
+            memcpy(p, chars_to_insert, insert_count);
+        }
+    }
+    if (convert_to_exp) {
+        int written;
+        size_t buf_avail;
+        p = digits_start;
+        /* insert decimal point */
+        assert(digit_count >= 1);
+        memmove(p+2, p+1, digit_count); /* safe, but overwrites nul */
+        p[1] = '.';
+        p += digit_count+1;
+        assert(p <= buf_size+buffer);
+        buf_avail = buf_size+buffer-p;
+        if (buf_avail == 0)
+            return NULL;
+        /* Add exponent.  It's okay to use lower case 'e': we only
+           arrive here as a result of using the empty format code or
+           repr/str builtins and those never want an upper case 'E' */
+        written = PyOS_snprintf(p, buf_avail, "e%+.02d", digit_count-1);
+        if (!(0 <= written &&
+              written < Py_SAFE_DOWNCAST(buf_avail, size_t, int)))
+            /* output truncated, or something else bad happened */
+            return NULL;
+        remove_trailing_zeros(buffer);
+    }
+    return buffer;
 }
 
@@ -389 +640 @@
  * @buf_size: The length of the buffer.
  * @format: The printf()-style format to use for the
- *          code to use for converting. 
+ *          code to use for converting.
  * @d: The #gdouble to convert
  *
@@ -395 +646 @@
  * decimal point. To format the number you pass in
  * a printf()-style format string. Allowed conversion
- * specifiers are 'e', 'E', 'f', 'F', 'g', 'G', and 'n'.
- * 
- * 'n' is the same as 'g', except it uses the current locale.
+ * specifiers are 'e', 'E', 'f', 'F', 'g', 'G', and 'Z'.
+ *
  * 'Z' is the same as 'g', except it always has a decimal and
  *     at least one digit after the decimal.
  *
  * Return value: The pointer to the buffer with the converted string.
+ * On failure returns NULL but does not set any Python exception.
  **/
 char *
-PyOS_ascii_formatd(char       *buffer, 
-                   size_t      buf_size, 
-                   const char *format, 
-                   double      d)
-{
-        char format_char;
-        size_t format_len = strlen(format);
-
-        /* For type 'n', we need to make a copy of the format string, because
-           we're going to modify 'n' -> 'g', and format is const char*, so we
-           can't modify it directly.  FLOAT_FORMATBUFLEN should be longer than
-           we ever need this to be.  There's an upcoming check to ensure it's
-           big enough. */
-        /* Issue 2264: code 'Z' requires copying the format.  'Z' is 'g', but
-           also with at least one character past the decimal. */
-        char tmp_format[FLOAT_FORMATBUFLEN];
-
-        /* The last character in the format string must be the format char */
-        format_char = format[format_len - 1];
-
-        if (format[0] != '%')
-                return NULL;
-
-        /* I'm not sure why this test is here.  It's ensuring that the format
-           string after the first character doesn't have a single quote, a
-           lowercase l, or a percent. This is the reverse of the commented-out
-           test about 10 lines ago. */
-        if (strpbrk(format + 1, "'l%"))
-                return NULL;
-
-        /* Also curious about this function is that it accepts format strings
-           like "%xg", which are invalid for floats.  In general, the
-           interface to this function is not very good, but changing it is
-           difficult because it's a public API. */
-
-        if (!(format_char == 'e' || format_char == 'E' || 
-              format_char == 'f' || format_char == 'F' || 
-              format_char == 'g' || format_char == 'G' ||
-              format_char == 'n' || format_char == 'Z'))
-                return NULL;
-
-        /* Map 'n' or 'Z' format_char to 'g', by copying the format string and
-           replacing the final char with a 'g' */
-        if (format_char == 'n' || format_char == 'Z') {
-                if (format_len + 1 >= sizeof(tmp_format)) {
-                        /* The format won't fit in our copy.  Error out.  In
-                           practice, this will never happen and will be
-                           detected by returning NULL */
-                        return NULL;
-                }
-                strcpy(tmp_format, format);
-                tmp_format[format_len - 1] = 'g';
-                format = tmp_format;
-        }
-
-
-        /* Have PyOS_snprintf do the hard work */
-        PyOS_snprintf(buffer, buf_size, format, d);
-
-        /* Do various fixups on the return string */
-
-        /* Get the current locale, and find the decimal point string.
-           Convert that string back to a dot.  Do not do this if using the
-           'n' (number) format code, since we want to keep the localized
-           decimal point in that case. */
-        if (format_char != 'n')
-                change_decimal_from_locale_to_dot(buffer);
-
-        /* If an exponent exists, ensure that the exponent is at least
-           MIN_EXPONENT_DIGITS digits, providing the buffer is large enough
-           for the extra zeros.  Also, if there are more than
-           MIN_EXPONENT_DIGITS, remove as many zeros as possible until we get
-           back to MIN_EXPONENT_DIGITS */
-        ensure_minimum_exponent_length(buffer, buf_size);
-
-        /* If format_char is 'Z', make sure we have at least one character
-           after the decimal point (and make sure we have a decimal point). */
-        if (format_char == 'Z')
-                ensure_decimal_point(buffer, buf_size);
-
-        /* If format_char is 'n', add the thousands grouping. */
-        if (format_char == 'n')
-                if (!add_thousands_grouping(buffer, buf_size))
-                        return NULL;
-
-        return buffer;
-}
-
-double
-PyOS_ascii_atof(const char *nptr)
-{
-        return PyOS_ascii_strtod(nptr, NULL);
-}
+_PyOS_ascii_formatd(char       *buffer,
+                   size_t      buf_size,
+                   const char *format,
+                   double      d,
+                   int         precision)
+{
+    char format_char;
+    size_t format_len = strlen(format);
+
+    /* Issue 2264: code 'Z' requires copying the format.  'Z' is 'g', but
+       also with at least one character past the decimal. */
+    char tmp_format[FLOAT_FORMATBUFLEN];
+
+    /* The last character in the format string must be the format char */
+    format_char = format[format_len - 1];
+
+    if (format[0] != '%')
+        return NULL;
+
+    /* I'm not sure why this test is here.  It's ensuring that the format
+       string after the first character doesn't have a single quote, a
+       lowercase l, or a percent. This is the reverse of the commented-out
+       test about 10 lines ago. */
+    if (strpbrk(format + 1, "'l%"))
+        return NULL;
+
+    /* Also curious about this function is that it accepts format strings
+       like "%xg", which are invalid for floats.  In general, the
+       interface to this function is not very good, but changing it is
+       difficult because it's a public API. */
+
+    if (!(format_char == 'e' || format_char == 'E' ||
+          format_char == 'f' || format_char == 'F' ||
+          format_char == 'g' || format_char == 'G' ||
+          format_char == 'Z'))
+        return NULL;
+
+    /* Map 'Z' format_char to 'g', by copying the format string and
+       replacing the final char with a 'g' */
+    if (format_char == 'Z') {
+        if (format_len + 1 >= sizeof(tmp_format)) {
+            /* The format won't fit in our copy.  Error out.  In
+               practice, this will never happen and will be
+               detected by returning NULL */
+            return NULL;
+        }
+        strcpy(tmp_format, format);
+        tmp_format[format_len - 1] = 'g';
+        format = tmp_format;
+    }
+
+
+    /* Have PyOS_snprintf do the hard work */
+    PyOS_snprintf(buffer, buf_size, format, d);
+
+    /* Do various fixups on the return string */
+
+    /* Get the current locale, and find the decimal point string.
+       Convert that string back to a dot. */
+    change_decimal_from_locale_to_dot(buffer);
+
+    /* If an exponent exists, ensure that the exponent is at least
+       MIN_EXPONENT_DIGITS digits, providing the buffer is large enough
+       for the extra zeros.  Also, if there are more than
+       MIN_EXPONENT_DIGITS, remove as many zeros as possible until we get
+       back to MIN_EXPONENT_DIGITS */
+    ensure_minimum_exponent_length(buffer, buf_size);
+
+    /* If format_char is 'Z', make sure we have at least one character
+       after the decimal point (and make sure we have a decimal point);
+       also switch to exponential notation in some edge cases where the
+       extra character would produce more significant digits that we
+       really want. */
+    if (format_char == 'Z')
+        buffer = ensure_decimal_point(buffer, buf_size, precision);
+
+    return buffer;
+}
+
+char *
+PyOS_ascii_formatd(char       *buffer,
+                   size_t      buf_size,
+                   const char *format,
+                   double      d)
+{
+    if (PyErr_WarnEx(PyExc_DeprecationWarning,
+                     "PyOS_ascii_formatd is deprecated, "
+                     "use PyOS_double_to_string instead", 1) < 0)
+        return NULL;
+
+    return _PyOS_ascii_formatd(buffer, buf_size, format, d, -1);
+}
+
+#ifdef PY_NO_SHORT_FLOAT_REPR
+
+/* The fallback code to use if _Py_dg_dtoa is not available. */
+
+PyAPI_FUNC(char *) PyOS_double_to_string(double val,
+                                         char format_code,
+                                         int precision,
+                                         int flags,
+                                         int *type)
+{
+    char format[32];
+    Py_ssize_t bufsize;
+    char *buf;
+    int t, exp;
+    int upper = 0;
+
+    /* Validate format_code, and map upper and lower case */
+    switch (format_code) {
+    case 'e':          /* exponent */
+    case 'f':          /* fixed */
+    case 'g':          /* general */
+        break;
+    case 'E':
+        upper = 1;
+        format_code = 'e';
+        break;
+    case 'F':
+        upper = 1;
+        format_code = 'f';
+        break;
+    case 'G':
+        upper = 1;
+        format_code = 'g';
+        break;
+    case 'r':          /* repr format */
+        /* Supplied precision is unused, must be 0. */
+        if (precision != 0) {
+            PyErr_BadInternalCall();
+            return NULL;
+        }
+        /* The repr() precision (17 significant decimal digits) is the
+           minimal number that is guaranteed to have enough precision
+           so that if the number is read back in the exact same binary
+           value is recreated.  This is true for IEEE floating point
+           by design, and also happens to work for all other modern
+           hardware. */
+        precision = 17;
+        format_code = 'g';
+        break;
+    default:
+        PyErr_BadInternalCall();
+        return NULL;
+    }
+
+    /* Here's a quick-and-dirty calculation to figure out how big a buffer
+       we need.  In general, for a finite float we need:
+
+         1 byte for each digit of the decimal significand, and
+
+         1 for a possible sign
+         1 for a possible decimal point
+         2 for a possible [eE][+-]
+         1 for each digit of the exponent;  if we allow 19 digits
+           total then we're safe up to exponents of 2**63.
+         1 for the trailing nul byte
+
+       This gives a total of 24 + the number of digits in the significand,
+       and the number of digits in the significand is:
+
+         for 'g' format: at most precision, except possibly
+           when precision == 0, when it's 1.
+         for 'e' format: precision+1
+         for 'f' format: precision digits after the point, at least 1
+           before.  To figure out how many digits appear before the point
+           we have to examine the size of the number.  If fabs(val) < 1.0
+           then there will be only one digit before the point.  If
+           fabs(val) >= 1.0, then there are at most
+
+         1+floor(log10(ceiling(fabs(val))))
+
+           digits before the point (where the 'ceiling' allows for the
+           possibility that the rounding rounds the integer part of val
+           up).  A safe upper bound for the above quantity is
+           1+floor(exp/3), where exp is the unique integer such that 0.5
+           <= fabs(val)/2**exp < 1.0.  This exp can be obtained from
+           frexp.
+
+       So we allow room for precision+1 digits for all formats, plus an
+       extra floor(exp/3) digits for 'f' format.
+
+    */
+
+    if (Py_IS_NAN(val) || Py_IS_INFINITY(val))
+        /* 3 for 'inf'/'nan', 1 for sign, 1 for '\0' */
+        bufsize = 5;
+    else {
+        bufsize = 25 + precision;
+        if (format_code == 'f' && fabs(val) >= 1.0) {
+            frexp(val, &exp);
+            bufsize += exp/3;
+        }
+    }
+
+    buf = PyMem_Malloc(bufsize);
+    if (buf == NULL) {
+        PyErr_NoMemory();
+        return NULL;
+    }
+
+    /* Handle nan and inf. */
+    if (Py_IS_NAN(val)) {
+        strcpy(buf, "nan");
+        t = Py_DTST_NAN;
+    } else if (Py_IS_INFINITY(val)) {
+        if (copysign(1., val) == 1.)
+            strcpy(buf, "inf");
+        else
+            strcpy(buf, "-inf");
+        t = Py_DTST_INFINITE;
+    } else {
+        t = Py_DTST_FINITE;
+        if (flags & Py_DTSF_ADD_DOT_0)
+            format_code = 'Z';
+
+        PyOS_snprintf(format, sizeof(format), "%%%s.%i%c",
+                      (flags & Py_DTSF_ALT ? "#" : ""), precision,
+                      format_code);
+        _PyOS_ascii_formatd(buf, bufsize, format, val, precision);
+    }
+
+    /* Add sign when requested.  It's convenient (esp. when formatting
+     complex numbers) to include a sign even for inf and nan. */
+    if (flags & Py_DTSF_SIGN && buf[0] != '-') {
+        size_t len = strlen(buf);
+        /* the bufsize calculations above should ensure that we've got
+           space to add a sign */
+        assert((size_t)bufsize >= len+2);
+        memmove(buf+1, buf, len+1);
+        buf[0] = '+';
+    }
+    if (upper) {
+        /* Convert to upper case. */
+        char *p1;
+        for (p1 = buf; *p1; p1++)
+            *p1 = Py_TOUPPER(*p1);
+    }
+
+    if (type)
+        *type = t;
+    return buf;
+}
+
+#else
+
+/* _Py_dg_dtoa is available. */
+
+/* I'm using a lookup table here so that I don't have to invent a non-locale
+   specific way to convert to uppercase */
+#define OFS_INF 0
+#define OFS_NAN 1
+#define OFS_E 2
+
+/* The lengths of these are known to the code below, so don't change them */
+static char *lc_float_strings[] = {
+    "inf",
+    "nan",
+    "e",
+};
+static char *uc_float_strings[] = {
+    "INF",
+    "NAN",
+    "E",
+};
+
+
+/* Convert a double d to a string, and return a PyMem_Malloc'd block of
+   memory contain the resulting string.
+
+   Arguments:
+     d is the double to be converted
+     format_code is one of 'e', 'f', 'g', 'r'.  'e', 'f' and 'g'
+       correspond to '%e', '%f' and '%g';  'r' corresponds to repr.
+     mode is one of '0', '2' or '3', and is completely determined by
+       format_code: 'e' and 'g' use mode 2; 'f' mode 3, 'r' mode 0.
+     precision is the desired precision
+     always_add_sign is nonzero if a '+' sign should be included for positive
+       numbers
+     add_dot_0_if_integer is nonzero if integers in non-exponential form
+       should have ".0" added.  Only applies to format codes 'r' and 'g'.
+     use_alt_formatting is nonzero if alternative formatting should be
+       used.  Only applies to format codes 'e', 'f' and 'g'.  For code 'g',
+       at most one of use_alt_formatting and add_dot_0_if_integer should
+       be nonzero.
+     type, if non-NULL, will be set to one of these constants to identify
+       the type of the 'd' argument:
+     Py_DTST_FINITE
+     Py_DTST_INFINITE
+     Py_DTST_NAN
+
+   Returns a PyMem_Malloc'd block of memory containing the resulting string,
+    or NULL on error. If NULL is returned, the Python error has been set.
+ */
+
+static char *
+format_float_short(double d, char format_code,
+                   int mode, Py_ssize_t precision,
+                   int always_add_sign, int add_dot_0_if_integer,
+                   int use_alt_formatting, char **float_strings, int *type)
+{
+    char *buf = NULL;
+    char *p = NULL;
+    Py_ssize_t bufsize = 0;
+    char *digits, *digits_end;
+    int decpt_as_int, sign, exp_len, exp = 0, use_exp = 0;
+    Py_ssize_t decpt, digits_len, vdigits_start, vdigits_end;
+    _Py_SET_53BIT_PRECISION_HEADER;
+
+    /* _Py_dg_dtoa returns a digit string (no decimal point or exponent).
+       Must be matched by a call to _Py_dg_freedtoa. */
+    _Py_SET_53BIT_PRECISION_START;
+    digits = _Py_dg_dtoa(d, mode, precision, &decpt_as_int, &sign,
+                         &digits_end);
+    _Py_SET_53BIT_PRECISION_END;
+
+    decpt = (Py_ssize_t)decpt_as_int;
+    if (digits == NULL) {
+        /* The only failure mode is no memory. */
+        PyErr_NoMemory();
+        goto exit;
+    }
+    assert(digits_end != NULL && digits_end >= digits);
+    digits_len = digits_end - digits;
+
+    if (digits_len && !Py_ISDIGIT(digits[0])) {
+        /* Infinities and nans here; adapt Gay's output,
+           so convert Infinity to inf and NaN to nan, and
+           ignore sign of nan. Then return. */
+
+        /* ignore the actual sign of a nan */
+        if (digits[0] == 'n' || digits[0] == 'N')
+            sign = 0;
+
+        /* We only need 5 bytes to hold the result "+inf\0" . */
+        bufsize = 5; /* Used later in an assert. */
+        buf = (char *)PyMem_Malloc(bufsize);
+        if (buf == NULL) {
+            PyErr_NoMemory();
+            goto exit;
+        }
+        p = buf;
+
+        if (sign == 1) {
+            *p++ = '-';
+        }
+        else if (always_add_sign) {
+            *p++ = '+';
+        }
+        if (digits[0] == 'i' || digits[0] == 'I') {
+            strncpy(p, float_strings[OFS_INF], 3);
+            p += 3;
+
+            if (type)
+                *type = Py_DTST_INFINITE;
+        }
+        else if (digits[0] == 'n' || digits[0] == 'N') {
+            strncpy(p, float_strings[OFS_NAN], 3);
+            p += 3;
+
+            if (type)
+                *type = Py_DTST_NAN;
+        }
+        else {
+            /* shouldn't get here: Gay's code should always return
+               something starting with a digit, an 'I',  or 'N' */
+            strncpy(p, "ERR", 3);
+            p += 3;
+            assert(0);
+        }
+        goto exit;
+    }
+
+    /* The result must be finite (not inf or nan). */
+    if (type)
+        *type = Py_DTST_FINITE;
+
+
+    /* We got digits back, format them.  We may need to pad 'digits'
+       either on the left or right (or both) with extra zeros, so in
+       general the resulting string has the form
+
+         [<sign>]<zeros><digits><zeros>[<exponent>]
+
+       where either of the <zeros> pieces could be empty, and there's a
+       decimal point that could appear either in <digits> or in the
+       leading or trailing <zeros>.
+
+       Imagine an infinite 'virtual' string vdigits, consisting of the
+       string 'digits' (starting at index 0) padded on both the left and
+       right with infinite strings of zeros.  We want to output a slice
+
+         vdigits[vdigits_start : vdigits_end]
+
+       of this virtual string.  Thus if vdigits_start < 0 then we'll end
+       up producing some leading zeros; if vdigits_end > digits_len there
+       will be trailing zeros in the output.  The next section of code
+       determines whether to use an exponent or not, figures out the
+       position 'decpt' of the decimal point, and computes 'vdigits_start'
+       and 'vdigits_end'. */
+    vdigits_end = digits_len;
+    switch (format_code) {
+    case 'e':
+        use_exp = 1;
+        vdigits_end = precision;
+        break;
+    case 'f':
+        vdigits_end = decpt + precision;
+        break;
+    case 'g':
+        if (decpt <= -4 || decpt >
+            (add_dot_0_if_integer ? precision-1 : precision))
+            use_exp = 1;
+        if (use_alt_formatting)
+            vdigits_end = precision;
+        break;
+    case 'r':
+        /* convert to exponential format at 1e16.  We used to convert
+           at 1e17, but that gives odd-looking results for some values
+           when a 16-digit 'shortest' repr is padded with bogus zeros.
+           For example, repr(2e16+8) would give 20000000000000010.0;
+           the true value is 20000000000000008.0. */
+        if (decpt <= -4 || decpt > 16)
+            use_exp = 1;
+        break;
+    default:
+        PyErr_BadInternalCall();
+        goto exit;
+    }
+
+    /* if using an exponent, reset decimal point position to 1 and adjust
+       exponent accordingly.*/
+    if (use_exp) {
+        exp = decpt - 1;
+        decpt = 1;
+    }
+    /* ensure vdigits_start < decpt <= vdigits_end, or vdigits_start <
+       decpt < vdigits_end if add_dot_0_if_integer and no exponent */
+    vdigits_start = decpt <= 0 ? decpt-1 : 0;
+    if (!use_exp && add_dot_0_if_integer)
+        vdigits_end = vdigits_end > decpt ? vdigits_end : decpt + 1;
+    else
+        vdigits_end = vdigits_end > decpt ? vdigits_end : decpt;
+
+    /* double check inequalities */
+    assert(vdigits_start <= 0 &&
+           0 <= digits_len &&
+           digits_len <= vdigits_end);
+    /* decimal point should be in (vdigits_start, vdigits_end] */
+    assert(vdigits_start < decpt && decpt <= vdigits_end);
+
+    /* Compute an upper bound how much memory we need. This might be a few
+       chars too long, but no big deal. */
+    bufsize =
+        /* sign, decimal point and trailing 0 byte */
+        3 +
+
+        /* total digit count (including zero padding on both sides) */
+        (vdigits_end - vdigits_start) +
+
+        /* exponent "e+100", max 3 numerical digits */
+        (use_exp ? 5 : 0);
+
+    /* Now allocate the memory and initialize p to point to the start of
+       it. */
+    buf = (char *)PyMem_Malloc(bufsize);
+    if (buf == NULL) {
+        PyErr_NoMemory();
+        goto exit;
+    }
+    p = buf;
+
+    /* Add a negative sign if negative, and a plus sign if non-negative
+       and always_add_sign is true. */
+    if (sign == 1)
+        *p++ = '-';
+    else if (always_add_sign)
+        *p++ = '+';
+
+    /* note that exactly one of the three 'if' conditions is true,
+       so we include exactly one decimal point */
+    /* Zero padding on left of digit string */
+    if (decpt <= 0) {
+        memset(p, '0', decpt-vdigits_start);
+        p += decpt - vdigits_start;
+        *p++ = '.';
+        memset(p, '0', 0-decpt);
+        p += 0-decpt;
+    }
+    else {
+        memset(p, '0', 0-vdigits_start);
+        p += 0 - vdigits_start;
+    }
+
+    /* Digits, with included decimal point */
+    if (0 < decpt && decpt <= digits_len) {
+        strncpy(p, digits, decpt-0);
+        p += decpt-0;
+        *p++ = '.';
+        strncpy(p, digits+decpt, digits_len-decpt);
+        p += digits_len-decpt;
+    }
+    else {
+        strncpy(p, digits, digits_len);
+        p += digits_len;
+    }
+
+    /* And zeros on the right */
+    if (digits_len < decpt) {
+        memset(p, '0', decpt-digits_len);
+        p += decpt-digits_len;
+        *p++ = '.';
+        memset(p, '0', vdigits_end-decpt);
+        p += vdigits_end-decpt;
+    }
+    else {
+        memset(p, '0', vdigits_end-digits_len);
+        p += vdigits_end-digits_len;
+    }
+
+    /* Delete a trailing decimal pt unless using alternative formatting. */
+    if (p[-1] == '.' && !use_alt_formatting)
+        p--;
+
+    /* Now that we've done zero padding, add an exponent if needed. */
+    if (use_exp) {
+        *p++ = float_strings[OFS_E][0];
+        exp_len = sprintf(p, "%+.02d", exp);
+        p += exp_len;
+    }
+  exit:
+    if (buf) {
+        *p = '\0';
+        /* It's too late if this fails, as we've already stepped on
+           memory that isn't ours. But it's an okay debugging test. */
+        assert(p-buf < bufsize);
+    }
+    if (digits)
+        _Py_dg_freedtoa(digits);
+
+    return buf;
+}
+
+
+PyAPI_FUNC(char *) PyOS_double_to_string(double val,
+                                         char format_code,
+                                         int precision,
+                                         int flags,
+                                         int *type)
+{
+    char **float_strings = lc_float_strings;
+    int mode;
+
+    /* Validate format_code, and map upper and lower case. Compute the
+       mode and make any adjustments as needed. */
+    switch (format_code) {
+    /* exponent */
+    case 'E':
+        float_strings = uc_float_strings;
+        format_code = 'e';
+        /* Fall through. */
+    case 'e':
+        mode = 2;
+        precision++;
+        break;
+
+    /* fixed */
+    case 'F':
+        float_strings = uc_float_strings;
+        format_code = 'f';
+        /* Fall through. */
+    case 'f':
+        mode = 3;
+        break;
+
+    /* general */
+    case 'G':
+        float_strings = uc_float_strings;
+        format_code = 'g';
+        /* Fall through. */
+    case 'g':
+        mode = 2;
+        /* precision 0 makes no sense for 'g' format; interpret as 1 */
+        if (precision == 0)
+            precision = 1;
+        break;
+
+    /* repr format */
+    case 'r':
+        mode = 0;
+        /* Supplied precision is unused, must be 0. */
+        if (precision != 0) {
+            PyErr_BadInternalCall();
+            return NULL;
+        }
+        break;
+
+    default:
+        PyErr_BadInternalCall();
+        return NULL;
+    }
+
+    return format_float_short(val, format_code, mode, precision,
+                              flags & Py_DTSF_SIGN,
+                              flags & Py_DTSF_ADD_DOT_0,
+                              flags & Py_DTSF_ALT,
+                              float_strings, type);
+}
+#endif /* ifdef PY_NO_SHORT_FLOAT_REPR */