Network, Computer and Programming Resources

Instruction mmx - PACKSSWB/PACKSSDW—Pack with Signed Saturation

Packs and saturates signed words into bytes (PACKSSWB) or signed doublewords into words (PACKSSDW). The PACKSSWB instruction packs 4 signed words from the destination operand (first operand) and 4 signed words from the source operand (second operand) into 8 signed bytes in the destination operand. If the signed value of a word is beyond the range of a signed byte (that is, greater than 7FH or less than 80H), the saturated byte value of 7FH or 80H, respectively, is stored into the destination. The PACKSSDW instruction packs 2 signed doublewords from the destination operand (first operand) and 2 signed doublewords from the source operand (second operand) into 4 signed words in the destination operand. If the signed value of a doubleword is beyond the range of a signed word (that is, greater than 7FFFH or less than 8000H), the saturated word value of 7FFFH or 8000H, respectively, is stored into the destination. The destination operand for either the PACKSSWB or PACKSSDW instruction must be an MMX technology register; the source operand may be either an MMX technology register or a quadword memory location.