source: vendor/FreeBSD-libc/current/gdtoa/arithchk.c

/****************************************************************
Copyright (C) 1997, 1998 Lucent Technologies
All Rights Reserved

Permission to use, copy, modify, and distribute this software and
its documentation for any purpose and without fee is hereby
granted, provided that the above copyright notice appear in all
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not be used in advertising or publicity pertaining to
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permission.

LUCENT DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.
IN NO EVENT SHALL LUCENT OR ANY OF ITS ENTITIES BE LIABLE FOR ANY
SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER
IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
THIS SOFTWARE.
****************************************************************/

/* Try to deduce arith.h from arithmetic properties. */

#include <stdio.h>

 static int dalign;
 typedef struct
Akind {
        char *name;
        int   kind;
        } Akind;

 static Akind
IEEE_8087       = { "IEEE_8087", 1 },
IEEE_MC68k      = { "IEEE_MC68k", 2 },
IBM             = { "IBM", 3 },
VAX             = { "VAX", 4 },
CRAY            = { "CRAY", 5};

 static Akind *
Lcheck()
{
        union {
                double d;
                long L[2];
                } u;
        struct {
                double d;
                long L;
                } x[2];

        if (sizeof(x) > 2*(sizeof(double) + sizeof(long)))
                dalign = 1;
        u.L[0] = u.L[1] = 0;
        u.d = 1e13;
        if (u.L[0] == 1117925532 && u.L[1] == -448790528)
                return &IEEE_MC68k;
        if (u.L[1] == 1117925532 && u.L[0] == -448790528)
                return &IEEE_8087;
        if (u.L[0] == -2065213935 && u.L[1] == 10752)
                return &VAX;
        if (u.L[0] == 1267827943 && u.L[1] == 704643072)
                return &IBM;
        return 0;
        }

 static Akind *
icheck()
{
        union {
                double d;
                int L[2];
                } u;
        struct {
                double d;
                int L;
                } x[2];

        if (sizeof(x) > 2*(sizeof(double) + sizeof(int)))
                dalign = 1;
        u.L[0] = u.L[1] = 0;
        u.d = 1e13;
        if (u.L[0] == 1117925532 && u.L[1] == -448790528)
                return &IEEE_MC68k;
        if (u.L[1] == 1117925532 && u.L[0] == -448790528)
                return &IEEE_8087;
        if (u.L[0] == -2065213935 && u.L[1] == 10752)
                return &VAX;
        if (u.L[0] == 1267827943 && u.L[1] == 704643072)
                return &IBM;
        return 0;
        }

char *emptyfmt = "";    /* avoid possible warning message with printf("") */

 static Akind *
ccheck()
{
        union {
                double d;
                long L;
                } u;
        long Cray1;

        /* Cray1 = 4617762693716115456 -- without overflow on non-Crays */
        Cray1 = printf(emptyfmt) < 0 ? 0 : 4617762;
        if (printf(emptyfmt, Cray1) >= 0)
                Cray1 = 1000000*Cray1 + 693716;
        if (printf(emptyfmt, Cray1) >= 0)
                Cray1 = 1000000*Cray1 + 115456;
        u.d = 1e13;
        if (u.L == Cray1)
                return &CRAY;
        return 0;
        }

 static int
fzcheck()
{
        double a, b;
        int i;

        a = 1.;
        b = .1;
        for(i = 155;; b *= b, i >>= 1) {
                if (i & 1) {
                        a *= b;
                        if (i == 1)
                                break;
                        }
                }
        b = a * a;
        return b == 0.;
        }

main()
{
        Akind *a = 0;
        int Ldef = 0;
        FILE *f;

#ifdef WRITE_ARITH_H    /* for Symantec's buggy "make" */
        f = fopen("arith.h", "w");
        if (!f) {
                printf("Cannot open arith.h\n");
                return 1;
                }
#else
        f = stdout;
#endif

        if (sizeof(double) == 2*sizeof(long))
                a = Lcheck();
        else if (sizeof(double) == 2*sizeof(int)) {
                Ldef = 1;
                a = icheck();
                }
        else if (sizeof(double) == sizeof(long))
                a = ccheck();
        if (a) {
                fprintf(f, "#define %s\n#define Arith_Kind_ASL %d\n",
                        a->name, a->kind);
                if (Ldef)
                        fprintf(f, "#define Long int\n#define Intcast (int)(long)\n");
                if (dalign)
                        fprintf(f, "#define Double_Align\n");
                if (sizeof(char*) == 8)
                        fprintf(f, "#define X64_bit_pointers\n");
#ifndef NO_LONG_LONG
                if (sizeof(long long) < 8)
#endif
                        fprintf(f, "#define NO_LONG_LONG\n");
                if (a->kind <= 2 && fzcheck())
                        fprintf(f, "#define Sudden_Underflow\n");
                return 0;
                }
        fprintf(f, "/* Unknown arithmetic */\n");
        return 1;
        }