hurr.c

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

static double normalize(double input) {
    if (input < 0.08145)
        return input / 4.5;
    else
        return pow(((input + 0.0993) / 1.0993), (1.0/0.45));
}

static void YCBCR_TO_RGB(int y, int cb, int cr, int *r, int *g, int *b) {
    double e_y = ((double)(y) / pow(2.0, 0.0) - 16.0) / 219.0;
    double e_cb = ((double)(cb) / pow(2.0, 0.0) - 128.0) / 224.0;
    double e_cr = ((double)(cr) / pow(2.0, 0.0) - 128.0) / 224.0;

    printf("y=%f cb=%f cr=%f\n", (double)y, (double)cb, (double)cr);
    printf("e_y=%f e_cb=%f, e_cr=%f\n", e_y, e_cb, e_cr);

    double e_r = (e_y + 1.5747*e_cr);
    double e_g = (e_y + (-0.1873*e_cb) + (-0.4682*e_cr));
    double e_b = (e_y + 1.8556*e_cb);

    printf("e_r=%f e_g=%f, e_b=%f\n"
           "n_r=%f n_g=%f n_b=%f\n",
           e_r * 255, e_g * 255, e_b * 255,
           normalize(e_r) * 255, normalize(e_g) * 255, normalize(e_b) * 255);
}

int main() {
    int r=1;
    int g=2;
    int b=3;

    YCBCR_TO_RGB(180, 128, 128, &r, &g, &b);
    YCBCR_TO_RGB(16, 128, 128, &r, &g, &b);
    YCBCR_TO_RGB(145, 147, 44, &r, &g, &b);

    printf("r=%d g=%d b=%d\n", r, g, b);

    return 0;
}

Compiles with

gcc -Wall -Wextra -std=c99 -pedantic -lm -o hurr hurr.c