Intel ARCHITECTURE IA-32 User Manual

Coding for SIMD Architectures 3
3-29
Performing SIMD operations on the original AoS format can require
more calculations and some of the operations do not take advantage of
all of the SIMD elements available. Therefore, this option is generally
less efficient.
The recommended way for computing data in AoS format is to swizzle
each set of elements to SoA format before processing it using SIMD
technologies. This swizzling can either be done dynamically during
program execution or statically when the data structures are generated;
see Chapters 4 and 5 for specific examples of swizzling code.
Performing the swizzle dynamically is usually better than using AoS,
addps xmm1, xmm0 ; xmm0 = DC, DC, DC,
; x0*xF+z0*zF
movaps xmm2, xmm1
shufps xmm2, xmm2,55h ; xmm2 = DC, DC, DC, y0*yF
addps xmm2, xmm1 ; xmm1 = DC, DC, DC,
; x0*xF+y0*yF+z0*zF
; SoA code
;
; X = x0,x1,x2,x3
; Y = y0,y1,y2,y3
; Z = z0,z1,z2,z3
; A = xF,xF,xF,xF
; B = yF,yF,yF,yF
; C = zF,zF,zF,zF
movaps xmm0, X ; xmm0 = x0,x1,x2,x3
movaps xmm1, Y ; xmm0 = y0,y1,y2,y3
movaps xmm2, Z ; xmm0 = z0,z1,z2,z3
mulps xmm0, A ; xmm0 = x0*xF, x1*xF, x2*xF, x3*xF
mulps xmm1, B ; xmm1 = y0*yF, y1*yF, y2*yF, y3*xF
mulps xmm2, C ; xmm2 = z0*zF, z1*zF, z2*zF, z3*zF
addps xmm0, xmm1
addps xmm0, xmm2 ; xmm0 = (x0*xF+y0*yF+z0*zF), ...
Example 3-16 AoS and SoA Code Samples (continued)

Intel ARCHITECTURE IA-32 Specifications

General

Instruction Set	x86
Instruction Set Type	CISC
Memory Segmentation	Supported
Operating Modes	Real mode, Protected mode, Virtual 8086 mode
Max Physical Address Size	36 bits (with PAE)
Max Virtual Address Size	32 bits
Architecture	IA-32 (Intel Architecture 32-bit)
Addressable Memory	4 GB (with Physical Address Extension up to 64 GB)
Floating Point Registers	8 x 80-bit
MMX Registers	8 x 64-bit
SSE Registers	8 x 128-bit
Registers	General-purpose registers (EAX, EBX, ECX, EDX, ESI, EDI, ESP, EBP), Segment registers (CS, DS, SS, ES, FS, GS), Instruction pointer (EIP), Flags register (EFLAGS)
Floating Point Unit	Yes (x87)