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Vol. 2A 3-571
INSTRUCTION SET REFERENCE, A-M
MAXPD—Return Maximum Packed Double-Precision Floating-Point Values
MAXPD—Return Maximum Packed Double-Precision Floating-Point
Values
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 destina-
tion 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).
Operation
DEST[63:0] ← IF ((DEST[63:0] = 0.0) and (SRC[63:0] = 0.0))
THEN SRC[63:0];
ELSE IF (DEST[63:0]
= SNaN) THEN SRC[63:0]; FI;
ELSE IF (SRC[63:0]
= SNaN) THEN SRC[63:0]; FI;
ELSE IF (DEST[63:0] > SRC[63:0])
THEN DEST[63:0];
ELSE SRC[63:0]; FI; FI;
DEST[127:64] ← IF ((DEST[127:64]
= 0.0) and (SRC[127:64] = 0.0))
THEN SRC[127:64];
ELSE IF (DEST[127:64]
= SNaN) THEN SRC[127:64]; FI;
ELSE IF (SRC[127:64]
= SNaN) THEN SRC[127:64]; FI;
ELSE IF (DEST[127:64] > SRC[63:0])
THEN DEST[127:64];
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
66 0F 5F /r MAXPD xmm1,
xmm2/m128
Valid Valid Return the maximum double-
precision floating-point values
between xmm2/m128 and xmm1.