VFPCLASSPH

VFPCLASSPH — Test Types of Packed FP16 Values

Opcode/ Instruction	Op/ En	64/32 Bit Mode Support	CPUID Feature Flag	Description
EVEX.128.NP.0F3A.W0 66 /r /ib VFPCLASSPH k1{k2}, xmm1/m128/m16bcst, imm8	A	V/V	(AVX512_FP16 AND AVX512VL) OR AVX10.1	Test the input for the following categories: NaN, +0, -0, +Infinity, -Infinity, denormal, finite negative. The immediate field provides a mask bit for each of these category tests. The masked test results are OR-ed together to form a mask result.
EVEX.256.NP.0F3A.W0 66 /r /ib VFPCLASSPH k1{k2}, ymm1/m256/m16bcst, imm8	A	V/V	(AVX512_FP16 AND AVX512VL) OR AVX10.1	Test the input for the following categories: NaN, +0, -0, +Infinity, -Infinity, denormal, finite negative. The immediate field provides a mask bit for each of these category tests. The masked test results are OR-ed together to form a mask result.
EVEX.512.NP.0F3A.W0 66 /r /ib VFPCLASSPH k1{k2}, zmm1/m512/m16bcst, imm8	A	V/V	AVX512_FP16 OR AVX10.1	Test the input for the following categories: NaN, +0, -0, +Infinity, -Infinity, denormal, finite negative. The immediate field provides a mask bit for each of these category tests. The masked test results are OR-ed together to form a mask result.

Instruction Operand Encoding

Op/En	Tuple	Operand 1	Operand 2	Operand 3	Operand 4
A	Full	ModRM:reg (w)	ModRM:r/m (r)	imm8 (r)	N/A

Description

This instruction checks the packed FP16 values in the source operand for special categories, specified by the set bits in the imm8 byte. Each set bit in imm8 specifies a category of floating-point values that the input data element is classified against; see Table 5-12 for the categories. The classified results of all specified categories of an input value are ORed together to form the final boolean result for the input element. The result is written to the corresponding bits in the destination mask register according to the writemask.

Table 5-12. Classifier Operations for VFPCLASSPH/VFPCLASSSH

Bits	Category	Classifier
imm8[0]	QNAN	Checks for QNAN
imm8[1]	PosZero	Checks +0
imm8[2]	NegZero	Checks for -0
imm8[3]	PosINF	Checks for +∞
imm8[4]	NegINF	Checks for −∞
imm8[5]	Denormal	Checks for Denormal
imm8[6]	Negative	Checks for Negative finite
imm8[7]	SNAN	Checks for SNAN

Operation

def check_fp_class_fp16(tsrc, imm8):
    negative ← tsrc[15]
    exponent_all_ones ← (tsrc[14:10] == 0x1F)
    exponent_all_zeros ← (tsrc[14:10] == 0)
    mantissa_all_zeros ← (tsrc[9:0] == 0)
    zero ← exponent_all_zeros and mantissa_all_zeros
    signaling_bit ← tsrc[9]
    snan ← exponent_all_ones and not(mantissa_all_zeros) and not(signaling_bit)
    qnan ← exponent_all_ones and not(mantissa_all_zeros) and signaling_bit
    positive_zero ← not(negative) and zero
    negative_zero ← negative and zero
    positive_infinity ← not(negative) and exponent_all_ones and mantissa_all_zeros
    negative_infinity ← negative and exponent_all_ones and mantissa_all_zeros
    denormal ← exponent_all_zeros and not(mantissa_all_zeros)
    finite_negative ← negative and not(exponent_all_ones) and not(zero)
    return (imm8[0] and qnan) OR
        (imm8[1] and positive_zero) OR
        (imm8[2] and negative_zero) OR
        (imm8[3] and positive_infinity) OR
        (imm8[4] and negative_infinity) OR
        (imm8[5] and denormal) OR
        (imm8[6] and finite_negative) OR
        (imm8[7] and snan)

VFPCLASSPH dest{k2}, src, imm8

VL = 128, 256 or 512
KL ← VL/16
FOR i ← 0 to KL-1:
    IF k2[i] or *no writemask*:
        IF SRC is memory and (EVEX.b = 1):
            tsrc ← SRC.fp16[0]
        ELSE:
            tsrc ← SRC.fp16[i]
        DEST.bit[i] ← check_fp_class_fp16(tsrc, imm8)
    ELSE:
        DEST.bit[i] ← 0

Intel C/C++ Compiler Intrinsic Equivalent

VFPCLASSPH __mmask8 _mm_fpclass_ph_mask (__m128h a, int imm8);
VFPCLASSPH __mmask8 _mm_mask_fpclass_ph_mask (__mmask8 k1, __m128h a, int imm8);
VFPCLASSPH __mmask16 _mm256_fpclass_ph_mask (__m256h a, int imm8);
VFPCLASSPH __mmask16 _mm256_mask_fpclass_ph_mask (__mmask16 k1, __m256h a, int imm8);
VFPCLASSPH __mmask32 _mm512_fpclass_ph_mask (__m512h a, int imm8);
VFPCLASSPH __mmask32 _mm512_mask_fpclass_ph_mask (__mmask32 k1, __m512h a, int imm8);

SIMD Floating-Point Exceptions

None.

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Source: Intel® 64 and IA-32 Architectures Software Developer's Manual, Combined Volumes (Order Number 325462-091US, March 2026)
Generated: 7-6-2026