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  1. #include <iso646.h>  // not, and
  2. #include <math.h>
  3. #include <stdbool.h>
  4. #include <stdio.h>
  5.  
  6. typedef bool (*func_t)(double);
  7.  
  8. bool is_negative_zero(double f) {
  9.   return signbit(f) and f >= 0;
  10. }
  11.  
  12. bool is_negative_zero_2(double f) {
  13.   return f == 0 and signbit(f);
  14. }
  15.  
  16. bool is_negative_zero_x(double f) {
  17.   return f == 0 and 1/f < 0;
  18. }
  19.  
  20. int test(func_t f, char* msg) {
  21.   int nerrors = 0;
  22.   double a[] = {0., 1., -1., 0./0., 1/0., -1/0., 0./(1/0.), 1./(1/0.), };
  23.   for (int i = 0; i < sizeof(a)/sizeof(*a); ++i) {
  24.     if (f(a[i])) {
  25.       ++nerrors;
  26.       fprintf(stderr, "error: %s f=%lf\n", msg, a[i]);
  27.     }
  28.   }
  29.   if (not (f(-0.) and f(-1./(1/0.)))) {
  30.     ++nerrors;
  31.     fprintf(stderr, "error: %s f=%s\n", msg, "-0.");
  32.   }
  33.   return nerrors;
  34. }
  35. int main() {
  36.   int nerrors = 0;
  37.   nerrors += test(is_negative_zero, "signbit");
  38.   nerrors += test(is_negative_zero_2, "x == 0 and signbit(x)");
  39.   nerrors += test(is_negative_zero_x, "1/x");
  40.   return (bool)nerrors;
  41. }
Success #stdin #stdout 0.01s 1716KB
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https://ideone.com/zqMl0
language:
C99 (gcc 8.3)
created:
12 years ago
visibility:
secret

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