Intel ARCHITECTURE IA-32 User Manual

Optimizing for SIMD Integer Applications 4
4-23
Building Blocks
This section describes instructions and algorithms which implement
common code building blocks efficiently.
Absolute Difference of Unsigned Numbers
Example 4-16 computes the absolute difference of two unsigned
numbers. It assumes an unsigned packed-byte data type. Here, we make
use of the subtract instruction with unsigned saturation. This instruction
receives
UNSIGNED operands and subtracts them with UNSIGNED
saturation. This support exists only for packed bytes and packed words,
not for packed doublewords.
This example will not work if the operands are signed.
Note that the
psadbw instruction may also be used in some situations;
see section “Packed Sum of Absolute Differences” for details.
Example 4-16 Absolute Difference of Two Unsigned Numbers
; Input:
; MM0 source operand
; MM1 source operand
; Output:
; MM0 absolute difference of the unsigned
; operands
movq MM2, MM0 ; make a copy of MM0
psubusb MM0, MM1 ; compute difference one way
psubusb MM1, MM2 ; compute difference the other way
por MM0, MM1 ; OR them together

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)