Here's a personal favorite of mine that I wrote a while back; I like it because it does what seems to be a slightly complicated problem to SIMD (count the numbe

Here's a personal favorite of mine that I wrote a while back; I like it because it does what seems to be a slightly complicated problem to SIMD (count the number of nonzero elements in a 16-element array of 16-bit values) and does it in a really small number of instructions: static inline int array_non_zero_count_mmx( int16_t *v ) { int count; asm( "pxor %%mm7, %%mm7 \n" "movq (%1), %%mm0 \n" "movq 8(%1), %%mm1 \n" "packsswb 16(%1), %%mm0 \n" "packsswb 24(%1), %%mm1 \n" "pcmpeqb %%mm7, %%mm0 \n" "pcmpeqb %%mm7, %%mm1 \n" "paddb %%mm0, %%mm1 \n" "psadbw %%mm7, %%mm1 \n" "movd %%mm1, %0 \n" :"=r"(count) :"r"(v) ); return (count+0x10)&0xff; } It is, not surprisingly, an order of magnitude faster than the C equivalent. Bonus points for understanding what the "0x10" is for at the end.