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Instruction mmx - PUNPCKLBW/PUNPCKLWD/PUNPCKLDQ—Unpack Low Packed Data

Unpacks and interleaves the low-order data elements (bytes, words, or doublewords) of the destination and source operands into the destination operand. The destination operand must be an MMX technology register; the source operand may be either an MMX technology register or a memory location. When source data comes from an MMX technology register, the upper 32 bits of the register are ignored. When the source data comes from a memory, only 32-bits are accessed from memory. The PUNPCKLBW instruction interleaves the four low-order bytes of the source operand and the four low-order bytes of the destination operand and writes them to the destination operand. The PUNPCKLWD instruction interleaves the two low-order words of the source operand and the two low-order words of the destination operand and writes them to the destination operand. The PUNPCKLDQ instruction interleaves the low-order doubleword of the source operand and the low-order doubleword of the destination operand and writes them to the destination operand. If the source operand is all zeros, the result (stored in the destination operand) contains zero extensions of the high-order data elements from the original value in the destination operand. With the PUNPCKLBW instruction the low-order bytes are zero extended (that is, unpacked into unsigned words), and with the PUNPCKLWD instruction, the low-order words are zero extended (unpacked into unsigned doublewords).