Changeset 679 for GPL/trunk/include/linux/log2.h

Timestamp:

Mar 18, 2021, 8:57:36 PM (4 years ago)

Author:

David Azarewicz

Message:

Merge changes from Paul's uniaud32next branch.

Location:

GPL/trunk

Files:

• . (modified) (1 prop)
• include/linux/log2.h (modified) (1 diff)

GPL/trunk/include/linux/log2.h

@@ -2 +2 @@
 #define _LINUX_LOG2_H
 
+#include <linux/bitops.h>
+#include <linux/types.h>
+
+/*
+ *  Determine whether some value is a power of two, where zero is
+ * *not* considered a power of two.
+ */
+
+static inline 
+bool is_power_of_2(unsigned long n)
+{
+        return (n != 0 && ((n & (n - 1)) == 0));
+}
+
+/**
+ * __roundup_pow_of_two() - round up to nearest power of two
+ * @n: value to round up
+ */
+static inline /*__attribute__((const))*/
+unsigned long __roundup_pow_of_two(unsigned long n)
+{
+        return 1UL << fls_long(n - 1);
+}
+
+/**
+ * __rounddown_pow_of_two() - round down to nearest power of two
+ * @n: value to round down
+ */
+static inline /*__attribute__((const))*/
+unsigned long __rounddown_pow_of_two(unsigned long n)
+{
+        return 1UL << (fls_long(n) - 1);
+}
+
+/***********************************************/
+/* Locate the position of the highest bit set. */
+/* A binary search is used.  The result is an  */
+/* approximation of log2(n) [the integer part] */
+/***********************************************/
+static inline int             ilog2(unsigned long n)
+{
+    int             i = (-1);
+
+    /* Is there a bit on in the high word? */
+    /* Else, all the high bits are already zero. */
+    if (n & 0xffff0000) {
+        i += 16;                /* Update our search position */
+        n >>= 16;               /* Shift out lower (irrelevant) bits */
+    }
+    /* Is there a bit on in the high byte of the current word? */
+    /* Else, all the high bits are already zero. */
+    if (n & 0xff00) {
+        i += 8;                 /* Update our search position */
+        n >>= 8;                /* Shift out lower (irrelevant) bits */
+    }
+    /* Is there a bit on in the current nybble? */
+    /* Else, all the high bits are already zero. */
+    if (n & 0xf0) {
+        i += 4;                 /* Update our search position */
+        n >>= 4;                /* Shift out lower (irrelevant) bits */
+    }
+    /* Is there a bit on in the high 2 bits of the current nybble? */
+    /* 0xc is 1100 in binary... */
+    /* Else, all the high bits are already zero. */
+    if (n & 0xc) {
+        i += 2;                 /* Update our search position */
+        n >>= 2;                /* Shift out lower (irrelevant) bits */
+    }
+    /* Is the 2nd bit on? [ 0x2 is 0010 in binary...] */
+    /* Else, all the 2nd bit is already zero. */
+    if (n & 0x2) {
+        i++;                    /* Update our search position */
+        n >>= 1;                /* Shift out lower (irrelevant) bit */
+    }
+    /* Is the lowest bit set? */
+    if (n)
+        i++;                    /* Update our search position */
+    return i;
+}
+
+/**
+ * roundup_pow_of_two - round the given value up to nearest power of two
+ * @n: parameter
+ *
+ * round the given value up to the nearest power of two
+ * - the result is undefined when n == 0
+ * - this can be used to initialise global variables from constant data
+ */
+#define roundup_pow_of_two(n)                   \
+(                                               \
+        __roundup_pow_of_two(n)                 \
+ )
+
+/**
+ * rounddown_pow_of_two - round the given value down to nearest power of two
+ * @n: parameter
+ *
+ * round the given value down to the nearest power of two
+ * - the result is undefined when n == 0
+ * - this can be used to initialise global variables from constant data
+ */
+#define rounddown_pow_of_two(n)                 \
+(                                               \
+        __rounddown_pow_of_two(n)               \
+ )
+
 #endif /* _LINUX_LOG2_H */