vmaxph

Maximum Packed FP16 Values

VMAXPH zmm1 {k1}, zmm2, zmm3/m512

Maximum of half-precision values.

Details

Computes the maximum of packed half-precision (FP16) values from two 512-bit sources, writing results to a 512-bit ZMM register under EVEX mask control. The instruction performs element-wise comparison following IEEE 754 semantics, with special handling for NaN and signed zero. No arithmetic flags are modified; this is a masked operation requiring AVX-512-FP16 support.

Pseudocode Operation

for i = 0 to 31:
  if (k1[i] == 1):
    zmm1[16*i:16*i+15] ← max_fp16(zmm2[16*i:16*i+15], zmm3/m512[16*i:16*i+15])
  else if (EVEX.z == 1):
    zmm1[16*i:16*i+15] ← 0
  // else zmm1[16*i:16*i+15] unchanged

Example

VMAXPH zmm1, zmm2, zmm3/m512

Encoding

Binary Layout

EVEX

Format EVEX

Opcode EVEX.512.NP.MAP5.W0 5F /r

Extension AVX-512-FP16

Operands

dest
512-bit ZMM AVX-512 register
src1
512-bit ZMM AVX-512 register
src2
512-bit ZMM AVX-512 register or Memory operand

Reference (Intel® SDM)

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
EVEX.128.NP.MAP5.W0 5F /r	VMAXPH xmm1{k1}{z}, xmm2, xmm3/m128/m16bcst	A	V/V	(AVX512_FP16 AND AVX512VL) OR AVX10.1	Return the maximum packed FP16 values between xmm2 and xmm3/m128/m16bcst and store the result in xmm1 subject to writemask k1.
EVEX.256.NP.MAP5.W0 5F /r	VMAXPH ymm1{k1}{z}, ymm2, ymm3/m256/m16bcst	A	V/V	(AVX512_FP16 AND AVX512VL) OR AVX10.1	Return the maximum packed FP16 values between ymm2 and ymm3/m256/m16bcst and store the result in ymm1 subject to writemask k1.
EVEX.512.NP.MAP5.W0 5F /r	VMAXPH zmm1{k1}{z}, zmm2, zmm3/m512/m16bcst {sae}	A	V/V	AVX512_FP16 OR AVX10.1	Return the maximum packed FP16 values between zmm2 and zmm3/m512/m16bcst and store the result in zmm1 subject to writemask k1.

Instruction Operand Encoding

Op/En	Tuple Type	Operand 1	Operand 2	Operand 3	Operand 4
A	Full	ModRM:reg (w)	VEX.vvvv (r)	ModRM:r/m (r)	N/A

Description

This instruction performs a SIMD compare of the packed FP16 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, then 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 VMAXPH can be emulated using a sequence of instructions, such as, a comparison followed by AND, ANDN and OR. EVEX encoded versions: The first source operand (the second operand) is a ZMM/YMM/XMM register. The second source operand can be a ZMM/YMM/XMM register, a 512/256/128-bit memory location or a 512/256/128-bit vector broadcast from a 16-bit memory location. The destination operand is a ZMM/YMM/XMM register conditionally updated with writemask k1.

Operation

def MAX(SRC1, SRC2):
IF (SRC1 = 0.0) and (SRC2 = 0.0):
DEST := SRC2
ELSE IF (SRC1 = NaN):
DEST := SRC2
ELSE IF (SRC2 = NaN):
DEST := SRC2
ELSE IF (SRC1 > SRC2):
DEST := SRC1
ELSE:
DEST := SRC2





VMAXPH—Return Maximum of Packed FP16 Values                                                                                             Vol. 2C 5-419
VMAXPH dest, src1, src2
VL = 128, 256 or 512
KL := VL/16

FOR j := 0 TO KL-1:
IF k1[j] OR *no writemask*:
IF EVEX.b = 1:
tsrc2 := SRC2.fp16[0]
ELSE:
tsrc2 := SRC2.fp16[j]
DEST.fp16[j] := MAX(SRC1.fp16[j], tsrc2)
ELSE IF *zeroing*:
DEST.fp16[j] := 0
// else dest.fp16[j] remains unchanged

DEST[MAXVL-1:VL] := 0

Intel C/C++ Compiler Intrinsic Equivalent

VMAXPH __m128h _mm_mask_max_ph (__m128h src, __mmask8 k, __m128h a, __m128h b);
VMAXPH __m128h _mm_maskz_max_ph (__mmask8 k, __m128h a, __m128h b);
VMAXPH __m128h _mm_max_ph (__m128h a, __m128h b);
VMAXPH __m256h _mm256_mask_max_ph (__m256h src, __mmask16 k, __m256h a, __m256h b);
VMAXPH __m256h _mm256_maskz_max_ph (__mmask16 k, __m256h a, __m256h b);
VMAXPH __m256h _mm256_max_ph (__m256h a, __m256h b);
VMAXPH __m512h _mm512_mask_max_ph (__m512h src, __mmask32 k, __m512h a, __m512h b);
VMAXPH __m512h _mm512_maskz_max_ph (__mmask32 k, __m512h a, __m512h b);
VMAXPH __m512h _mm512_max_ph (__m512h a, __m512h b);
VMAXPH __m512h _mm512_mask_max_round_ph (__m512h src, __mmask32 k, __m512h a, __m512h b, int sae);
VMAXPH __m512h _mm512_maskz_max_round_ph (__mmask32 k, __m512h a, __m512h b, int sae);
VMAXPH __m512h _mm512_max_round_ph (__m512h a, __m512h b, int sae);

Exceptions

SIMD Floating-Point Exceptions

Invalid, Denormal.

Other Exceptions

EVEX-encoded instructions, see Table 2-48, “Type E2 Class Exception Conditions.” VMAXPH—Return Maximum of Packed FP16 Values Vol. 2C 5-420