Intel® 64 and IA-32 Architectures Optimization Reference Manual

OPTIMIZING FOR SIMD INTEGER APPLICATIONSExample 5-5. Signed Unpack Code (Contd.)movdqa xmm1, xmm0 ; copy sourcepunpcklwd xmm0, xmm0 ; unpack four low end words of the source; into the upper 16 bits of each doubleword; in the destinationpunpckhwd xmm1, xmm1 ; unpack 4 high-end words of the source; into the upper 16 bits of each doubleword; in the destinationpsrad xmm0, 16 ; sign-extend the 4 low-end words of the source; into four 32-bit signed doublewordspsrad xmm1, 16 ; sign-extend the 4 high-end words of the; source into four 32-bit signed doublewords5.4.3 Interleaved Pack with SaturationPack instructions pack two values into a destination register in a predeterminedorder. PACKSSDW saturates two signed doublewords from a source operand and twosigned doublewords from a destination operand into four signed words; and it packsthe four signed words into a destination register. See Figure 5-1.SSE2 extends PACKSSDW so that it saturates four signed doublewords from a sourceoperand and four signed doublewords from a destination operand into eight signedwords; the eight signed words are packed into the destination.mm/m64mmD C B AD 1C 1B 1A 1mmOM15159Figure 5-1. PACKSSDW mm, mm/mm64 InstructionFigure 5-2 illustrates where two pairs of values are interleaved in a destinationregister; Example 5-6 shows MMX code that accomplishes the operation.5-8