Manipulation of the IEEE floating point representation.

ieee.c

#include <stdio.h>

int as_int(float f) {
    union { float f; int i; } u;
    u.f = f;
    return u.i;
}

float as_float(int i) {
    union { float f; int i; } u;
    u.i = i;
    return u.f;
}

float encode_float(int s, int e, int m) {
    return as_float(s | e << 23 | m & 0x7FFFFF);
}

float fracf(float f) {
    int i = as_int(f);
    int e = (i >> 23) & 0xFF;
    int m = i & 0x7FFFFF;
    return encode_float(0, 127, m << (e - 127)) - 1.0f;
}

int main() {
    printf("%f\n", fracf(-12877.212f));
    return 0;
}