PABSQ — absolute value of two singed 64-bit numbers

Author:	Wojciech Muła
Added on:	2008-06-08

Branch-less x86 code:

movl  %eax, %ebx
sarl   $32, %ebx        ; fill ebx with sign bit
xorl  %ebx, %eax        ; negate eax (if negative)
subl  %ebx, %eax        ; increment eax by 1 (if negative)

SSE2:

pshufd $0b11110101, %xmm0, %xmm1        ; populate dwords 3 and 1
psrad   $32, %xmm1      ; fill quad words with sign bit
pxor  %xmm1, %xmm0      ; negate (if negative)
psubq %xmm1, %xmm0      ; increment (if negative)