User Guide

64-Bit Media Programming 217
24592—Rev. 3.15—November 2009 AMD64 Technology
The subtraction instructions perform operations analogous to the addition instructions.
The PSUBB, PSUBW, PSUBD, and PSUBQ instructions subtract each 8-bit (PSUBB), 16-bit
(PSUBW), 32-bit (PSUBD), or 64-bit (PSUBQ) integer element in the second operand from the
corresponding, same-sized integer element in the first operand. The instructions then write the integer
result of each subtraction to the corresponding, same-sized element of the destination. These
instructions operate on both signed and unsigned integers. However, if the result underflows, only the
low-order byte, word, doubleword, or quadword of each result is written to the destination.
The PSUBSB and PSUBSW instructions perform subtractions analogous to the PSUBB and PSUBW
instructions, except with saturation. For each result in the destination, if the result is larger than the
largest, or smaller than the smallest, representable 8-bit (PSUBSB) or 16-bit (PSUBSW) signed
integer, the result is saturated to the largest or smallest representable value, respectively.
The PSUBUSB and PSUBUSW instructions perform saturating subtractions analogous to the
PSUBSB and PSUBSW instructions, except on unsigned integer elements.
Multiplication
• PMULHW—Packed Multiply High Signed Word
• PMULLW—Packed Multiply Low Signed Word
• PMULHRW—
Packed Multiply High Rounded Word
• PMULHUW—Packed Multiply High Unsigned Word
• PMULUDQ—Packed Multiply Unsigned Doubleword and Store Quadword
The PMULHW instruction multiplies each 16-bit signed integer value in first operand by the
corresponding 16-bit integer in the second operand, producing a 32-bit intermediate result. The
instruction then writes the high-order 16 bits of the 32-bit intermediate result of each multiplication to
the corresponding word of the destination. The PMULLW instruction performs the same
multiplication as PMULHW but writes the low-order 16 bits of the 32-bit intermediate result to the
corresponding word of the destination.
The PMULHRW instruction performs the same multiplication as PMULHW but with rounding. After
the multiplication, PMULHRW adds 8000h to the lower word of the doubleword result, thus rounding
the high-order word which is returned as the result.
The PMULHUW instruction performs the same multiplication as PMULHW but on unsigned
operands. The instruction is useful in 3D rasterization, which operates on unsigned pixel values.
The PMULUDQ instruction, unlike the other PMULx instructions, preserves the full precision of the
result. It multiplies 32-bit unsigned integer values in the first and second operands and writes the full
64-bit result to the destination.
See “Shift” on page 219 for shift instructions that can be used to perform multiplication and division
by powers of 2.