Intel® 64 and IA-32 Architectures Optimization Reference Manual

OPTIMIZING FOR SIMD INTEGER APPLICATIONSCode in the Example 5-8 unpacks two packed-word sources in a non-interleavedway. The goal is to use the instruction which unpacks doublewords to a quadword,instead of using the instruction which unpacks words to doublewords.Example 5-8. Unpacking Two Packed-word Sources in Non-interleaved Way Code; Input:; MM0 packed-word source value; MM1 packed-word source value; Output:; MM0 contains the two low-end words of the; original sources, non-interleaved; MM2 contains the two high end words of the; original sources, non-interleaved.movq mm2, mm0 ; copy source1punpckldq mm0, mm1 ; replace the two high-end words; of MMO with two low-end words of; MM1; leave the two low-end words; of MM0 in placepunpckhdq mm2, mm1 ; move two high-end words of MM2; to the two low-end words of MM2;; place the two high-end words of; MM1 in two high-end words of MM25.4.6 Extract WordThe PEXTRW instruction takes the word in the designated MMX register selected bythe two least significant bits of the immediate value and moves it to the lower half ofa 32-bit integer register. See Figure 5-5 and Example 5-9.63MM31 0X4 X3 X2 X1R3231 00 ..0 X1OM15163Figure 5-5. PEXTRW Instruction5-12