fast IEEE 754 float random

ffr.c

#include <stdint.h>
#include <stdlib.h>

// assert(RAND_MAX >= 0x7fff)
float 
random_0_to_1() {
  union {
    uint32_t d;
    float f;
  } u;
  u.d = (((uint32_t)rand() & 0x7fff) << 8) | 0x3f800000;
  return u.f - 1.0f;
}

float 
random_minus1_to_1() {
  union {
    uint32_t d;
    float f;
  } u;
  u.d = (((uint32_t)rand() & 0x7fff) << 8) | 0x40000000;
  return u.f - 3.0f;
}