Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1707

PACKSSWB/PACKSSDW—Pack with Signed Saturation
Opcode
0F 63 /r
0F 6B /r
Description
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 (see
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.
Figure 3-3.
Operation
IF instruction is PACKSSWB
THEN
DEST(7..0)  SaturateSignedWordToSignedByte DEST(15..0);
DEST(15..8)  SaturateSignedWordToSignedByte DEST(31..16);
DEST(23..16)  SaturateSignedWordToSignedByte DEST(47..32);
DEST(31..24)  SaturateSignedWordToSignedByte DEST(63..48);
DEST(39..32)  SaturateSignedWordToSignedByte SRC(15..0);
DEST(47..40)  SaturateSignedWordToSignedByte SRC(31..16);
DEST(55..48)  SaturateSignedWordToSignedByte SRC(47..32);
DEST(63..56)  SaturateSignedWordToSignedByte SRC(63..48);
®
Volume 4: IA-32 Intel MMX™ Technology Instruction Reference
Instruction Description
PACKSSWB mm, Packs and saturate pack 4 signed words from mm and 4
mm/m64 signed words from mm/m64 into 8 signed bytes in mm .
PACKSSDW mm, Pack and saturate 2 signed doublewords from mm and 2
mm/m64 signed doublewords from mm/m64 into 4 signed words in mm .
Operation of the PACKSSDW Instruction
PACKSSDW mm, mm/m64
mm/m64
C
D
D'
Figure 3-3). If the signed value of a
mm
A
B
C' B'
A'
mm
4:405