Intel® 64 and IA-32 Architectures Optimization Reference Manual

OPTIMIZING FOR SIMD INTEGER APPLICATIONSExample 5-4. Zero Extend 16-bit Values into 32 Bits Using Unsigned Unpack InstructionsCode; Input:; XMM0 8 16-bit values in source; XMM7 0 a local variable can be used; instead of the register XMM7 if; desired.; Output:; XMM0 four zero-extended 32-bit; doublewords from four low-end; words; XMM1 four zero-extended 32-bit; doublewords from four high-end; wordsmovdqa xmm1, xmm0 ; copy sourcepunpcklwd xmm0, xmm7 ; unpack the 4 low-end words; into 4 32-bit doublewordpunpckhwd xmm1, xmm7 ; unpack the 4 high-end words; into 4 32-bit doublewords5.4.2 Signed UnpackSigned numbers should be sign-extended when unpacking values. This is similar tothe zero-extend shown above, except that the PSRAD instruction (packed shift rightarithmetic) is used to sign extend the values.Example 5-5 assumes the source is a packed-word (16-bit) data type.Example 5-5. Signed Unpack CodeInput:; XMM0 source value; Output:; XMM0 four sign-extended 32-bit doublewords; from four low-end words; XMM1 four sign-extended 32-bit doublewords; from four high-end words;5-7