Function mpsnr_operator

Source/astcenccli_error_metrics.cpp:67–78

* @brief mPSNR tone-mapping operator for HDR images. * * @param val The color value to tone map * @param fstop The exposure fstop; should be in range [-125, 125] * * @return The mapped color value in [0.0f, 255.0f] range */

 * @return The mapped color value in [0.0f, 255.0f] range
 */
static float mpsnr_operator(
	float val,
	int fstop
) {
	// Fast implementation of pow(2.0, fstop), assuming IEEE float layout
	// Memcpy to uint avoids ubsan complaints shift of negative int
	unsigned int uscale = 0x3f800000u + (astc::int_as_uint(fstop) << 23);
	float scale = astc::uint_as_float(uscale);

	val = powf(val * scale, (1.0f / 2.2f));
	return astc::clamp(val * 255.0f, 0.0f, 255.0f);
}

/**
 * @brief mPSNR difference between two values.