kitty/3rdparty/base64/lib/arch/ssse3/dec_reshuffle.c

static inline __m128i
dec_reshuffle (const __m128i in)
{
	// in, bits, upper case are most significant bits, lower case are least significant bits
	// 00llllll 00kkkkLL 00jjKKKK 00JJJJJJ
	// 00iiiiii 00hhhhII 00ggHHHH 00GGGGGG
	// 00ffffff 00eeeeFF 00ddEEEE 00DDDDDD
	// 00cccccc 00bbbbCC 00aaBBBB 00AAAAAA

	const __m128i merge_ab_and_bc = _mm_maddubs_epi16(in, _mm_set1_epi32(0x01400140));
	// 0000kkkk LLllllll 0000JJJJ JJjjKKKK
	// 0000hhhh IIiiiiii 0000GGGG GGggHHHH
	// 0000eeee FFffffff 0000DDDD DDddEEEE
	// 0000bbbb CCcccccc 0000AAAA AAaaBBBB

	const __m128i out = _mm_madd_epi16(merge_ab_and_bc, _mm_set1_epi32(0x00011000));
	// 00000000 JJJJJJjj KKKKkkkk LLllllll
	// 00000000 GGGGGGgg HHHHhhhh IIiiiiii
	// 00000000 DDDDDDdd EEEEeeee FFffffff
	// 00000000 AAAAAAaa BBBBbbbb CCcccccc

	// Pack bytes together:
	return  _mm_shuffle_epi8(out, _mm_setr_epi8(
		 2,  1,  0,
		 6,  5,  4,
		10,  9,  8,
		14, 13, 12,
		-1, -1, -1, -1));
	// 00000000 00000000 00000000 00000000
	// LLllllll KKKKkkkk JJJJJJjj IIiiiiii
	// HHHHhhhh GGGGGGgg FFffffff EEEEeeee
	// DDDDDDdd CCcccccc BBBBbbbb AAAAAAaa
}