MAXPD (Return Maximum Packed Double-Precision Floating-Point Values)

Opcodes

Opcode/Instruction Op/En 64/32-bit Mode CPUID Feature Flag Description
66 0F 5F /r MAXPD xmm1, xmm2/m128 RM V/V SSE2 Return the maximum double-precision floating-point values between xmm2/m128 and xmm1.
VEX.NDS.128.66.0F.WIG 5F /r VMAXPD xmm1,xmm2, xmm3/m128 RVM V/V AVX Return the maximum double-precision floating-point values between xmm2 and xmm3/mem.
VEX.NDS.256.66.0F.WIG 5F /r VMAXPD ymm1, ymm2, ymm3/m256 RVM V/V AVX Return the maximum packed double-precision floating-point values between ymm2 and ymm3/mem.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
RM ModRM:reg (r, w) ModRM:r/m (r) NA NA
RVM ModRM:reg (w) VEX.vvvv (r) ModRM:r/m (r) NA

Description

Performs an SIMD compare of the packed double-precision floating-point values in the first source operand and the second source operand and returns the maximum value for each pair of values to the destination operand.

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).

128-bit Legacy SSE version: The second source can be an XMM register or an 128-bit memory location. The desti-nation is not distinct from the first source XMM register and the upper bits (VLMAX-1:128) of the corresponding YMM register destination are unmodified.

VEX.128 encoded version: the first source operand is an XMM register or 128-bit memory location. The destination operand is an XMM register. The upper bits (VLMAX-1:128) of the corresponding YMM register destination are zeroed.

VEX.256 encoded version: The first source operand is a YMM register. The second source operand can be a YMM register or a 256-bit memory location. The destination operand is a YMM register.

Operation

MAX(SRC1, SRC2)

{
    IF ((SRC1 = 0.0) and (SRC2 = 0.0)) THEN DEST ← SRC2;
         ELSE IF (SRC1 = SNaN) THEN DEST ← SRC2; FI;
         ELSE IF (SRC2 = SNaN) THEN DEST ← SRC2; FI;
         ELSE IF (SRC1 
 SRC2) THEN DEST ← SRC1;
         ELSE DEST ← SRC2;
    FI;
}

MAXPD (128-bit Legacy SSE version)

DEST[63:0] ← MAX(DEST[63:0], SRC[63:0])
DEST[127:64] ← MAX(DEST[127:64], SRC[127:64])
DEST[VLMAX-1:128] (Unmodified)

VMAXPD (VEX.128 encoded version)

DEST[63:0] ← MAX(SRC1[63:0], SRC2[63:0])
DEST[127:64] ← MAX(SRC1[127:64], SRC2[127:64])
DEST[VLMAX-1:128] ← 0

VMAXPD (VEX.256 encoded version)

DEST[63:0] ← MAX(SRC1[63:0], SRC2[63:0])
DEST[127:64] ← MAX(SRC1[127:64], SRC2[127:64])
DEST[191:128] ← MAX(SRC1[191:128], SRC2[191:128])
DEST[255:192] ← MAX(SRC1[255:192], SRC2[255:192])

Intel C/C++ Compiler Intrinsic Equivalent

MAXPD:

__m128d _mm_max_pd(__m128d a, __m128d b);

VMAXPD:

__m256d _mm256_max_pd (__m256d a, __m256d b);

SIMD Floating-Point Exceptions

Invalid (including QNaN source operand), Denormal.

Other Exceptions

See Exceptions Type 2.