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

I am coming a little late to the party, seeming that the community has already decided for poseur's pshufb-answer but distributing 2000 reputation, that is so extremely generous i have to give it a try.

Here's my version without platform specific intrinsics or machine-specific asm, i have included some cross-platform timing code showing a 4x speedup if you do both the bit-twiddling like me AND activate compiler-optimization (register-optimization, loop-unrolling):

#include "stdlib.h"
#include "stdio.h"
#include "time.h"

#define UInt8 unsigned char

#define IMAGESIZE (1920*1080) 
int main() {
    time_t  t0, t1;
    int frames;
    int frame; 
    typedef struct{ UInt8 Alpha; UInt8 Red; UInt8 Green; UInt8 Blue; } ARGB;
    typedef struct{ UInt8 Blue; UInt8 Green; UInt8 Red; } BGR;

    ARGB* orig = malloc(IMAGESIZE*sizeof(ARGB));
    if(!orig) {printf("nomem1");}
    BGR* dest = malloc(IMAGESIZE*sizeof(BGR));
    if(!dest) {printf("nomem2");}

    printf("to start original hit a key\n");
    getch();
    t0 = time(0);
    frames = 1200;
    for(frame = 0; frame

The results are these (on my core 2 subnotebook):

F:\>gcc b.c -o b.exe

F:\>b
to start original hit a key
finished original of 1200 frames in 16 seconds
to start alternative hit a key
finished alternative of 1200 frames in 10 seconds

F:\>gcc b.c -O3 -o b.exe

F:\>b
to start original hit a key
finished original of 1200 frames in 8 seconds
to start alternative hit a key
finished alternative of 1200 frames in 4 seconds