docs/probe_math_exception.c

   1 /* Small test program for probing how various math functions
   2  * with specific operands set floating point exceptions
   3  */
   4
   5 #define _ISOC99_SOURCE 1
   6 #define _GNU_SOURCE    1
   7
   8 #include <stdint.h>
   9 #include <math.h>
  10 #include <fenv.h>
  11 #include <stdio.h>
  12
  13 int main(int argc, char **argv)
  14 {
  15         float largest, small, t, inf_float;
  16
  17         largest = small = 1;
  18         while (1) {
  19                 t = largest + small;
  20                 /* optimizations may make plain "t == largest" unreliable */
  21                 if (memcmp(&t, &largest, sizeof(float)) == 0)
  22                         break;
  23                 if (isfinite(t)) {
  24                         largest = t;
  25                         small *= 2;
  26                         continue;
  27                 }
  28                 small /= 2;
  29         }
  30         inf_float = largest + largest;
  31         //printf("%.40g ", largest);
  32         //printf("[%llx]\n", (long long) (*(uint32_t *)&largest));
  33
  34         feclearexcept(FE_ALL_EXCEPT);
  35
  36         //t = 1.0 / 0.0; // simple test: FE_DIVBYZERO
  37         //t = nextafterf(largest, 1); // glibc 2.8: no math exceptions raised
  38         //t = nextafterf(largest, largest); // glibc 2.8: no math exceptions raised
  39         //t = nextafterf(largest, inf_float); // glibc 2.8: FE_INEXACT FE_OVERFLOW
  40
  41 #define PREX(ex) do { if (fetestexcept(ex)) printf(#ex " "); } while(0)
  42 #ifdef FE_INEXACT
  43         PREX(FE_INEXACT);
  44 #endif
  45 #ifdef FE_DIVBYZERO
  46         PREX(FE_DIVBYZERO);
  47 #endif
  48 #ifdef FE_UNDERFLOW
  49         PREX(FE_UNDERFLOW);
  50 #endif
  51 #ifdef FE_OVERFLOW
  52         PREX(FE_OVERFLOW);
  53 #endif
  54 #ifdef FE_INVALID
  55         PREX(FE_INVALID);
  56 #endif
  57         if (fetestexcept(FE_ALL_EXCEPT))
  58                 printf("\n");
  59         else
  60                 printf("no math exceptions raised\n");
  61
  62         printf("%.40g\n", t);
  63         return 0;
  64 }