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128-Bit Media and Scientific Programming 175
24592—Rev. 3.15—November 2009 AMD64 Technology
• ORPD—Logical Bitwise OR Packed Double-Precision Floating-Point
The ORPS instruction performs a logical bitwise OR of four single-precision floating-point values in
the first operand and the corresponding four single-precision floating-point values in the second
operand and writes the result in the destination. The ORPD instruction performs an analogous
operation on pairs of two double-precision floating-point values.
Exclusive Or
• XORPS—Logical Bitwise Exclusive OR Packed Single-Precision Floating-Point
• XORPD—Logical Bitwise Exclusive OR Packed Double-Precision Floating-Point
The XORPS instruction performs a logical bitwise exclusive OR of four single-precision floating-
point values in the first operand and the corresponding four single-precision floating-point values in
the second operand and writes the result in the destination. The XORPD instruction performs an
analogous operation on pairs of two double-precision floating-point values.
4.7 Instruction Effects on Flags
The STMXCSR and LDMXCSR instructions, described in “Save and Restore State” on page 156,
read and write flags in the MXCSR register. For a description of the MXCSR register, see “MXCSR
Register” on page 117.
The COMISS, COMISD, UCOMISS, and UCOMISD instructions, described in “Compare” on
page 171, write flag bits in the rFLAGS register. For a description of the rFLAGS register, see “Flags
Register” on page 33.
4.8 Instruction Prefixes
Instruction prefixes, in general, are described in “Instruction Prefixes” on page 71. The following
restrictions apply to the use of instruction prefixes with 128-bit media instructions.
4.8.1 Supported Prefixes
The following prefixes can be used with 128-bit media instructions:
• Address-Size Override—The 67h prefix affects only operands in memory. The prefix is ignored by
all other 128-bit media instructions.
• Operand-Size Override—The 66h prefix is used to form the opcodes of certain 128-bit media
instructions. The prefix is ignored by all other 128-bit media instructions.
• Segment Overrides—The 2Eh (CS), 36h (SS), 3Eh (DS), 26h (ES), 64h (FS), and 65h (GS)
prefixes affect only operands in memory. In 64-bit mode, the contents of the CS, DS, ES, SS
segment registers are ignored.