uniform half4 colorGreen, colorRed;

const int plus = 1;
const int minus = 2;
const int star = 3;
const int slash = 4;

bool test(int op, float m11, float m12, float m21, float m22, float2x2 expected) {

    float one = colorRed.r;

    float2x2 m2 = float2x2(m11 * one, m12 * one, m21 * one, m22 * one);
    switch (op) {
        case plus: m2 += 1; break;
        case minus: m2 -= 1; break;
        case star: m2 *= 2; break;
        case slash: m2 /= 2; break;
    }

    return m2[0][0] == expected[0][0] &&
           m2[0][1] == expected[0][1] &&
           m2[1][0] == expected[1][0] &&
           m2[1][1] == expected[1][1];
}

half4 main(float2 coords) {
    float f1 = 1 * colorGreen.g;
    float f2 = 2 * colorGreen.g;
    float f3 = 3 * colorGreen.g;
    float f4 = 4 * colorGreen.g;

    return true
           && test(plus, f1, f2, f3, f4, float2x2(f1+1, f2+1, f3+1, f4+1))
           && test(minus, f1, f2, f3, f4, float2x2(f1-1, f2-1, f3-1, f4-1))
           && test(star, f1, f2, f3, f4, float2x2(f1*2, f2*2, f3*2, f4*2))
           && test(slash, f1, f2, f3, f4, float2x2(f1/2, f2/2, f3/2, f4/2))
           ? colorGreen : colorRed;
}