Intel ARCHITECTURE IA-32 User Manual

Optimizing for SIMD Floating-point Applications 5
5-21
Use of cvttps2pi/cvttss2si Instructions
The cvttps2pi and cvttss2si instructions encode the truncate/chop
rounding mode implicitly in the instruction, thereby taking precedence
over the rounding mode specified in the
MXCSR register. This behavior
can eliminate the need to change the rounding mode from
round-nearest, to truncate/chop, and then back to round-nearest to
resume computation. Frequent changes to the
MXCSR register should be
Example 5-10 Horizontal Add Using Intrinsics with movhlps/movlhps
void horiz_add_intrin(Vertex_soa *in, float *out)
{
__m128 v1, v2, v3, v4;
__m128 tmm0,tmm1,tmm2,tmm3,tmm4,tmm5,tmm6;
// Temporary variables
tmm0 = _mm_load_ps(in->x); // tmm0 = A1 A2 A3 A4
tmm1 = _mm_load_ps(in->y); // tmm1 = B1 B2 B3 B4
tmm2 = _mm_load_ps(in->z); // tmm2 = C1 C2 C3 C4
tmm3 = _mm_load_ps(in->w); // tmm3 = D1 D2 D3 D4
tmm5 = tmm0; // tmm0 = A1 A2 A3 A4
tmm5 = _mm_movelh_ps(tmm5, tmm1); // tmm5 = A1 A2 B1 B2
tmm1 = _mm_movehl_ps(tmm1, tmm0); // tmm1 = A3 A4 B3 B4
tmm5 = _mm_add_ps(tmm5, tmm1); // tmm5 = A1+A3 A2+A4 B1+B3 B2+B4
tmm4 = tmm2;
tmm2 = _mm_movelh_ps(tmm2, tmm3); // tmm2 = C1 C2 D1 D2
tmm3 = _mm_movehl_ps(tmm3, tmm4); // tmm3 = C3 C4 D3 D4
tmm3 = _mm_add_ps(tmm3, tmm2); // tmm3 = C1+C3 C2+C4 D1+D3 D2+D4
tmm6 = tmm3; // tmm6 = C1+C3 C2+C4 D1+D3 D2+D4
tmm6 = _mm_shuffle_ps(tmm3, tmm5, 0xDD);
// tmm6 = A1+A3 B1+B3 C1+C3 D1+D3
tmm5 = _mm_shuffle_ps(tmm5, tmm6, 0x88);
// tmm5 = A2+A4 B2+B4 C2+C4 D2+D4
tmm6 = _mm_add_ps(tmm6, tmm5);
// tmm6 = A1+A2+A3+A4 B1+B2+B3+B4
// C1+C2+C3+C4 D1+D2+D3+D4
_mm_store_ps(out, tmm6);
}

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)