Unpack IEEE754 binary32, from "int[4]" to "float"

unpackIEEE754Binary32.glsl

float unpackIEEE754Binary32(int bytes[4]) {
	/**
	 bytes[0][0]: sign {1 if minus}
	 bytes[0][1:7]: exponent(0:6)
	 bytes[1][0]: exponent(7)
	 bytes[1][1:7]: fraction(0:6)
	 bytes[2][0:7]: fraction(7:14)
	 bytes[3][0:7]: fraction(15:22)
	 */
	
	bool minus = false;
	int exponent = 0;
	if (bytes[0] >= 128) {
		minus = true;
		exponent = (bytes[0] - 128) * 2;
	} else {
		exponent = bytes[0] * 2;
	}
	if (bytes[1] >= 127) {
		exponent += 1;
		bytes[1] -= 128;
	}
	exponent -= 127;
	
	float fraction = 1.0;
	float base = 0.5;
	int byteIndex = 1;
	int bitIndex = 1;
	int pow2 = 64; // pow2 = pow(2, 7 - bitIndex)
	for (; byteIndex < 4; ++byteIndex) {
		int b = bytes[byteIndex];
		for (; bitIndex < 8; ++bitIndex) {
			if (b >= pow2) {
				fraction += base;
				b -= pow2;
			}
			base *= 0.5;
			pow2 /= 2;
		}
		bitIndex = 0;
		pow2 = 128;
	}

	float v = fraction * pow(2.0, float(exponent));
	if (minus) {
		v *= -1.0;
	}
	return v;
}