Fast method to copy memory with translation - ARGB to BGR

Question

Overview

I have an image buffer that I need to convert to another format. The origin image buffer is four channels, 8 bits per channel, Alpha, Red, Green, and Blue

Answer 1

The obvious, using pshufb.

#include 
#include 
#include 

// needs:
// orig is 16-byte aligned
// imagesize is a multiple of 4
// dest has 4 trailing scratch bytes
void convert(uint8_t *orig, size_t imagesize, uint8_t *dest) {
    assert((uintptr_t)orig % 16 == 0);
    assert(imagesize % 4 == 0);
    __m128i mask = _mm_set_epi8(-128, -128, -128, -128, 13, 14, 15, 9, 10, 11, 5, 6, 7, 1, 2, 3);
    uint8_t *end = orig + imagesize * 4;
    for (; orig != end; orig += 16, dest += 12) {
        _mm_storeu_si128((__m128i *)dest, _mm_shuffle_epi8(_mm_load_si128((__m128i *)orig), mask));
    }
}