normalize_ftoi.c

#include <stdio.h>
#include <float.h>
#include <math.h>

// Takes a float in the range [-1.0, 1.0] and converts to an int in the range [INT_MIN, INT_MAX]
// NOTE: Floats outside of this range will be clamped
int normalized_ftoi(float f)
{
    // Clamp float to [-1.0, 1.0f]
    if (f > 1.0f) f = 1.0f;
    if (f < -1.0f) f = -1.0f;
    f /= 2.0f;
    
    // Calculate range of ints (in a bigger type to prevent overflow), then multiply by float
    long long range = (long long)INT_MAX - INT_MIN;
    long long lng = (long long)(f * range);

    // Clamp the long back into int range to prevent overflow
    if (lng < INT_MIN) lng = INT_MIN;
    if (lng > INT_MAX) lng = INT_MAX;

    // Convert to int
    return (int)lng;
}

int normalized_ftoi_test(float f, int expected)
{
    int i = normalized_ftoi(f);
    printf("%52.10f -> %12d == %12d (%s)\n", f, i, expected, i == expected ? "PASS" : "FAIL");
}

int main(int argc, char *argv[])
{
    normalized_ftoi_test(INFINITY,        INT_MAX);
    normalized_ftoi_test(FLT_MAX,         INT_MAX);
    normalized_ftoi_test(2.0f,            INT_MAX);
    normalized_ftoi_test(1.0f,            INT_MAX);
    normalized_ftoi_test(0.0000000008f,   3);
    normalized_ftoi_test(0.0000000006f,   2);
    normalized_ftoi_test(0.0000000004f,   1);
    normalized_ftoi_test(FLT_MIN,         0);
    normalized_ftoi_test(0.0f,            0);
    normalized_ftoi_test(-FLT_MIN,        0);
    normalized_ftoi_test(-0.0000000004f, -1);
    normalized_ftoi_test(-0.0000000006f, -2);
    normalized_ftoi_test(-0.0000000008f, -3);
    normalized_ftoi_test(-1.0f,           INT_MIN);
    normalized_ftoi_test(-2.0f,           INT_MIN);
    normalized_ftoi_test(-FLT_MAX,        INT_MIN);
    normalized_ftoi_test(-INFINITY,       INT_MIN);
    return 0;
}

// Output:
//                                                 inf ->   2147483647 ==   2147483647 (PASS)
//                                                 inf ->   2147483647 ==   2147483647 (PASS)
//  340282346638528859811704183484516925440.0000000000 ->   2147483647 ==   2147483647 (PASS)
//                                        2.0000000000 ->   2147483647 ==   2147483647 (PASS)
//                                        1.0000000000 ->   2147483647 ==   2147483647 (PASS)
//                                        0.0000000008 ->            3 ==            3 (PASS)
//                                        0.0000000006 ->            2 ==            2 (PASS)
//                                        0.0000000004 ->            1 ==            1 (PASS)
//                                        0.0000000000 ->            0 ==            0 (PASS)
//                                        0.0000000000 ->            0 ==            0 (PASS)
//                                       -0.0000000000 ->            0 ==            0 (PASS)
//                                       -0.0000000004 ->           -1 ==           -1 (PASS)
//                                       -0.0000000006 ->           -2 ==           -2 (PASS)
//                                       -0.0000000008 ->           -3 ==           -3 (PASS)
//                                       -1.0000000000 ->  -2147483648 ==  -2147483648 (PASS)
//                                       -2.0000000000 ->  -2147483648 ==  -2147483648 (PASS)
// -340282346638528859811704183484516925440.0000000000 ->  -2147483648 ==  -2147483648 (PASS)
//                                                -inf ->  -2147483648 ==  -2147483648 (PASS)