i32_error.c

//this will show that that conversion error for i32 and f32 is 64 and ~2.98023224e-8 respectively
//(0.0000000298023223876953125 in normal notation, or about 3 ten millionths of a percent)

#define RANGE 100000000

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

int get_random_i32(){
    union {
      struct {
          uint16_t l;
          uint16_t h;
      };
      int32_t i;
    } output;
    output.l=rand();
    output.h=rand();
    return output.i;
}

//multiplying by inv32 is equivalent to dividing by 0x7fffffff
const float inv32=1.0f/0x7fffffff;
int32_t convert_from_and_to(int32_t input){
    float from=(float)input*inv32;
    return from*2147483647; //to
}

int main(){
    time_t t;
    srand((unsigned)time(&t));

    int32_t mn=0,mx=0;
    for(int i=0; i<RANGE; ++i){
        int32_t src=get_random_i32();
        int32_t dst=convert_from_and_to(src);
        int32_t dif=dst-src;
        if(dif<mn) mn=dif;
        if(dif>mx) mx=dif;
        //printf("%11i -> %11i (%i)\n",src,dst, dif);
    }
    //given enough RANGE, this should end up being -64 and 64 respectively
    printf("min=%i, max=%i\n",mn,mx);

    return 0;
}