MAXPD

Return Maximum Packed Double-Precision Floating-Point Values

Opcodes

Hex	Mnemonic	Encoding	Long Mode	Legacy Mode	Description
66 0F 5F /r	MAXPD xmm1, xmm2/m128	A	Valid	Valid	Return the maximum double-precision floating-point values between xmm2/m128 and xmm1.

Instruction Operand Encoding

Op/En	Operand 0	Operand 1	Operand 2	Operand 3
A	NA	NA	ModRM:r/m (r)	ModRM:reg (r, w)

Description

Performs a SIMD compare of the packed double-precision floating-point values in the destination operand (first operand) and the source operand (second operand), and returns the maximum value for each pair of values to the destination operand. The source operand can be an XMM register or a 128-bit memory location. The destination operand is an XMM register.

If the values being compared are both 0.0s (of either sign), the value in the second operand (source operand) is returned. If a value in the second operand is an SNaN, that SNaN is forwarded unchanged to the destination (that is, a QNaN version of the SNaN is not returned).

If only one value is a NaN (SNaN or QNaN) for this instruction, the second operand (source operand), either a NaN or a valid floating-point value, is written to the result. If instead of this behavior, it is required that the NaN source operand (from either the first or second operand) be returned, the action of MAXPD can be emulated using a sequence of instructions, such as, a comparison followed by AND, ANDN and OR.

In 64-bit mode, use of the REX.R prefix permits this instruction to access additional registers (XMM8-XMM15).

Pseudo Code

DEST[63:0] =
IF ((DEST[63:0] = 0.0) and (SRC[63:0] = 0.0))
	SRC[63:0];
ELSE
	IF (DEST[63:0] = SNaN)
		SRC[63:0];
	ELSE
		IF (SRC[63:0] = SNaN)
			SRC[63:0];
		ELSE
			IF (DEST[63:0] > SRC[63:0])
				DEST[63:0];
			ELSE
				SRC[63:0];
			FI;
		FI;
	FI;
FI;
DEST[127:64] =
IF ((DEST[127:64] = 0.0) and (SRC[127:64] = 0.0))
	SRC[127:64];
ELSE
	IF (DEST[127:64] = SNaN)
		SRC[127:64];
	ELSE
		IF (SRC[127:64] = SNaN)
			SRC[127:64];
		ELSE
			IF (DEST[127:64] > SRC[63:0])
				DEST[127:64];
			ELSE
				SRC[127:64];
			FI;
		FI;
	FI;
FI;

Exceptions

SIMD Floating-Point Exceptions

Invalid (including QNaN source operand), Denormal.

64-Bit Mode Exceptions

Exception	Description
#UD	If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 0. If CR0.EM[bit 2] = 1. If CR4.OSFXSR[bit 9] = 0. If CPUID.01H:EDX.SSE2[bit 26] = 0. If the LOCK prefix is used.
#XM	If an unmasked SIMD floating-point exception and CR4.OSXM MEXCPT[bit 10] = 1.
#NM	If CR0.TS[bit 3] = 1.
#PF(fault-code)	For a page fault.
#GP(0)	If the memory address is in a non-canonical form. If memory operand is not aligned on a 16-byte boundary, regardless of segment.
#SS(0)	If a memory address referencing the SS segment is in a non-canonical form.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

Virtual-8086 Mode Exceptions

Exception	Description
#PF(fault-code)	For a page fault.
Same exceptions as in real address mode.

Real-Address Mode Exceptions

Exception	Description
#UD	If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 0. If CR0.EM[bit 2] = 1. If CR4.OSFXSR[bit 9] = 0. If CPUID.01H:EDX.SSE2[bit 26] = 0. If the LOCK prefix is used.
#XM	If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 1.
#NM	If CR0.TS[bit 3] = 1.
#GP	If a memory operand is not aligned on a 16-byte boundary, regardless of segment. If any part of the operand lies outside the effective address space from 0 to FFFFH.

Protected Mode Exceptions

Exception	Description
#UD	If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 0. If CR0.EM[bit 2] = 1. If CR4.OSFXSR[bit 9] = 0. If CPUID.01H:EDX.SSE2[bit 26] = 0. If the LOCK prefix is used.
#XM	If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 1.
#NM	If CR0.TS[bit 3] = 1.
#PF(fault-code)	For a page fault.
#SS(0)	If a memory operand effective address is outside the SS segment limit.
#GP(0)	For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments. If a memory operand is not aligned on a 16-byte boundary, regardless of segment.