compute affine transform

affine.c

/* clang affine.c -Wextra */

/*
./a.out 1
1.000000 in [-1 1] = 255 in [0 255]
./a.out 0
0.000000 in [-1 1] = 127 in [0 255]
./a.out -1
-1.000000 in [-1 1] = 0 in [0 255]
*/

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

/* for x in [a, b] compute y in [c, d] */
uint8_t affine(float x, float a, float b, float c, float d)
{
    return (x - a) * ( (d - c) / (b - a) ) + c;
}


int main(int argc, char *argv[])
{
    if(!argv[1]) goto fail;

    float x;
    sscanf(argv[1],"%f", &x);

    if(x < -1.0f || x > 1.0f) goto fail;

    uint8_t ret = affine(x, -1, 1, 0, 255);
    printf("%f in [%d %d] = %d in [%d %d]\n", x, -1, 1, ret, 0, 255);
    return ret;

fail:
    puts("pass a number in range [-1, 1]"); return -1;
}