fast_ftol.c

#include <stdint.h>

int fast_ftol(float x) {
    union {
        float f;
        uint32_t i;
    } float_conv;
    uint32_t mantissa;
    int exponent;
    int result;

    /* load float in union */
    float_conv.f = x;

    /* extract the mantissa (the lowest 23 bits number) */
    mantissa = float_conv.i & 0x7fffff;
    
    /* the IEEE754 float assumes the highest bit on the mantissa is set, so set it */
    mantissa |= 0x800000;
    
    /* extract exponent (which is biased, so we unbias as well */
    exponent = 150 - ((float_conv.i >> 23) & 0xff);
    
    /* calculate the integer value */
    result = mantissa;
    
    if (exponent < 0) {
        result <<= -exponent;
    } else {
        result >>= exponent;
    }
    
    /* handle sign */
    if (float_conv.i & 0x80000000) {
        result = -result;
    }

    return result;
}