Intel® 64 and IA-32 Architectures Optimization Reference Manual

OPTIMIZING FOR SIMD INTEGER APPLICATIONS5.6.1 Absolute Difference of Unsigned NumbersExample 5-18 computes the absolute difference of two unsigned numbers. Itassumes an unsigned packed-byte data type.Here, we make use of the subtract instruction with unsigned saturation. This instructionreceives UNSIGNED operands and subtracts them with UNSIGNED saturation.This support exists only for packed bytes and packed words, not for packed doublewords.Example 5-18. Absolute Difference of Two Unsigned Numbers; Input:; MM0 source operand; MM1 source operand; Output:; MM0absolute difference of the unsigned; operandsmovq mm2, mm0 ; make a copy of mm0psubusbmm0, mm1 ; compute difference one waypsubusbmm1, mm2 ; compute difference the other waypor mm0, mm1 ; OR them togetherThis example will not work if the operands are signed. Note that PSADBW may alsobe used in some situations. See Section 5.6.9 for details.5.6.2 Absolute Difference of Signed NumbersExample 5-19 computes the absolute difference of two signed numbers using SSSE3instruction PABSW. This sequence is more efficient than using previous generation ofSIMD instruction extensions.Example 5-19. Absolute Difference of Signed Numbers;Input:; XMM0 signed source operand; XMM1 signed source operand;Output:; XMM1absolute difference of the unsigned; operandspsubw xmm0, xmm1 ; subtract wordspabsw xmm1, xmm0 ; results in XMM15-20