Function clz

external/astc-encoder/Source/astcenc_vecmathlib.h:437–452

* @brief Count the leading zeros for each lane in @c a. * * Valid for all data values of @c a; will return a per-lane value [0, 32]. */

 * Valid for all data values of @c a; will return a per-lane value [0, 32].
 */
static ASTCENC_SIMD_INLINE vint4 clz(vint4 a)
{
	// This function is a horrible abuse of floating point exponents to convert
	// the original integer value into a 2^N encoding we can recover easily.

	// Convert to float without risk of rounding up by keeping only top 8 bits.
	// This trick is is guaranteed to keep top 8 bits and clear the 9th.
	a = (~lsr<8>(a)) & a;
	a = float_as_int(int_to_float(a));

	// Extract and unbias exponent
	a = vint4(127 + 31) - lsr<23>(a);

	// Clamp result to a valid 32-bit range
	return clamp(0, 32, a);
}

/**
 * @brief Return lanewise 2^a for each lane in @c a.