math_signaling_nan/signaling_nan_test1.c
Posted by Anonymous on Wed 7th Jun 2023 18:21
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/*
 * math_signaling_nan/signaling_nan_test1.c - SNAN/signaling nan playground
 *
 *
 * Compile with:
 * $ gcc -fsignaling-nans -g -Wall signaling_nan_test1.c -lm #
 *
 */

#define _GNU_SOURCE 1
#define __STDC_WANT_IEC_60559_BFP_EXT__ 1

#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <signal.h>

/*
 * See $ gcc -fsignaling-nans -D__STDC_WANT_IEC_60559_BFP_EXT__ \
 * -E -dM -include math.h - < /dev/null 2>&1 | grep -F 'builtin_nan'
 * to see defines
 */

#ifndef __SUPPORT_SNAN__
#error __SUPPORT_SNAN__ not set
#endif

const uint64_t double_quiet_NaN =               0x7FF8000000000000;
const uint64_t double_signaling_NaN =           0x7FF0000001000000;
const uint64_t double_quiet_location_bit =      0x0008000000000000;

void catch_mathsig(int sig, siginfo_t *info, void *ucontext)
{
        feclearexcept(FE_INVALID);
        feclearexcept(FE_ALL_EXCEPT);
        (void)printf("math error = %d, si_code=%d\n", sig, info->si_code);
}


void printbytes(const void *mem, size_t si)
{
        const unsigned char *m = mem;
        size_t i;

        for(i=0 ; i < si ; i++) {
                (void)printf("%2.2x", m[i]);
        }
        (void)puts("");
}

void printdoublelayout(double *d)
{
        printbytes(d, sizeof(*d));

        /* this is not portable! */
        if (sizeof(double) == sizeof(long)) {
                uint64_t float_bits = *((unsigned long *)((void *)d));
                (void)printf("%lx (snan=%s)\n",
                        float_bits,
                        ((float_bits & double_quiet_location_bit)?
                                "false":"true"));
        }
}

int main(int ac, char *av[])
{
        (void)puts("# start.");

        (void)puts("# mark sigaction.");
        struct sigaction sact;
        sact.sa_sigaction = catch_mathsig;
        sigemptyset (&sact.sa_mask);
        sact.sa_flags = SA_SIGINFO;
#if 0
        sigaction(SIGFPE, &sact, (struct sigaction *)0);
        feenableexcept(FE_ALL_EXCEPT);
#endif
        (void)puts("# mark print quiet nan.");
        double fq = NAN;

        (void)printf("fq=%f\n", fq);
        printdoublelayout(&fq);

        double fs = SNAN;

        (void)puts("# mark sin().");
        sin(fs);
#if 0
        (void)puts("# mark sqrt().");
        sqrt(-2);
#endif
        (void)puts("# mark print signaling nan.");
        (void)printf("fs=%f\n", fs);
        printdoublelayout(&fs);

        if (fs != fq)
                (void)puts("fs != fq");
        if (fs == fq)
                (void)puts("fs == fq");

        (void)puts("# done.");
        return EXIT_SUCCESS;
}