random.h - tomo

(28 lines)
   1 // This file defines some wrapper logic around different systems' random functions
   2 
   3 #include <assert.h>
   4 #include <stdint.h>
   5 
   6 #if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__APPLE__)
   7 #include <stdlib.h>
   8 static ssize_t getrandom(void *buf, size_t buflen, unsigned int flags) {
   9     (void)flags;
  10     arc4random_buf(buf, buflen);
  11     return buflen;
  12 }
  13 #elif defined(__linux__)
  14 // Use getrandom()
  15 #include <sys/random.h>
  16 #else
  17 #error "Unsupported platform for secure random number generation"
  18 #endif
  19 
  20 static int64_t random_range(int64_t low, int64_t high) {
  21     uint64_t range = (uint64_t)high - (uint64_t)low + 1;
  22     uint64_t min_r = -range % range;
  23     uint64_t r;
  24     do {
  25         assert(getrandom(&r, sizeof(r), 0) == sizeof(r));
  26     } while (r < min_r);
  27     return (int64_t)((uint64_t)low + (r % range));
  28 }