gistfile1.c

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

/* IEEE-754 values taken from page 2 of:
 * "Introduction to Floating point calculations and IEEE 754 standard"
 * Jamil Khatib, August 10, 2000
 */

typedef uint32_t uint;

const uint shift = 32-8-1; /* 4*sizeof(float) - exp bits - sign bits */
const uint mask = 0xff;
const uint bias = 126; /* exp bias - 1 */

int main(int argc, char **argv)
{
    float f, frac;
    int x, e, n;

    f = 3.14159f;
    if (argc > 1)
        f = atof(argv[1]);
    x = *(uint*)&f;
    e = (x>>shift)&mask - bias;
    if (e < 32-8)
        x &= ~(1<<(32-8-e) - 1);
    n = *(float*)&x;
    frac = f - n;
    printf("%d, %f\n", n, frac);
    return 0;
}