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IA-32 Intel® Architecture Optimization
5-14
Data Deswizzling
In the deswizzle operation, we want to arrange the SoA format back into
AoS format so the
xxxx, yyyy, zzzz are rearranged and stored in
memory as
xyz. To do this we can use the unpcklps/unpckhps
instructions to regenerate the
xyxy layout and then store each half (xy)
into its corresponding memory location using
movlps/movhps followed
by another
movlps/movhps to store the z component.
Example 5-5 illustrates the deswizzle function:
Example 5-5 Deswizzling Single-Precision SIMD Data
void deswizzle_asm(Vertex_soa *in, Vertex_aos *out)
{
__asm {
mov ecx, in // load structure addresses
mov edx, out
movaps xmm7, [ecx] // load x1 x2 x3 x4 => xmm7
movaps xmm6, [ecx+16] // load y1 y2 y3 y4 => xmm6
movaps xmm5, [ecx+32] // load z1 z2 z3 z4 => xmm5
movaps xmm4, [ecx+48] // load w1 w2 w3 w4 => xmm4
// START THE DESWIZZLING HERE
movaps xmm0, xmm7 // xmm0= x1 x2 x3 x4
unpcklps xmm7, xmm6 // xmm7= x1 y1 x2 y2
movlps [edx], xmm7 // v1 = x1 y1 -- --
movhps [edx+16], xmm7 // v2 = x2 y2 -- --
unpckhps xmm0, xmm6 // xmm0= x3 y3 x4 y4
movlps [edx+32], xmm0 // v3 = x3 y3 -- --
movhps [edx+48], xmm0 // v4 = x4 y4 -- --
movaps xmm0, xmm5 // xmm0= z1 z2 z3 z4
continued