branchless_merge.c

// Branchless merge (7 cycles/elem on Zen 3)
void merge1(u32 *dest, const u32 *src1, const u32 *end1, const u32 *src2, const u32 *end2) {
	for (;;) {
		if (unlikely(src1 == end1)) {
			memcpy(dest, src2, (end2 - src2) * sizeof(u32));
			return;
		}
		if (unlikely(src2 == end2)) {
			memcpy(dest, src1, (end1 - src1) * sizeof(u32));
			return;
		}
		u32 val1 = *src1;
		u32 val2 = *src2;
		int cond = val1 <= val2;
		*dest++ = cond ? val1 : val2;
		src1 = cond ? src1 + 1 : src1;
		src2 = cond ? src2 : src2 + 1;
	}
}

// Bidirectional branchless merge (3.5 cycles/elem on Zen 3)
void merge2(u32 *dest, const u32 *src1, const u32 *end1, const u32 *src2, const u32 *end2) {
	u32 *end = dest + (end1 - src1) + (end2 - src2);
	for (;;) {
		if (unlikely(src1 + 1 >= end1 || src2 + 1 >= end2))
			return merge1(dest, src1, end1, src2, end2);
		// Front
		u32 val1 = *src1;
		u32 val2 = *src2;
		int cond = val1 <= val2;
		*dest++ = cond ? val1 : val2;
		src1 = cond ? src1 + 1 : src1;
		src2 = cond ? src2 : src2 + 1;
		// Back
		val1 = end1[-1];
		val2 = end2[-1];
		cond = val1 > val2;
		*--end = cond ? val1 : val2;
		end1 = cond ? end1 - 1 : end1;
		end2 = cond ? end2 : end2 - 1;
	}
}

May I ask what is the license for this snippet? Would it be possible to reuse it in an LGPLv2 project?