VCVTNEPS2BF16 — Convert Packed Single Data to Packed BF16 Data

Opcode/Instruction Op/En 64/32 bit Mode Support CPUID Feature Flag Description
EVEX.128.F3.0F38.W0 72 /r VCVTNEPS2BF16 xmm1{k1}{z}, xmm2/m128/m32bcst A V/V AVX512VL AVX512_BF16 Convert packed single data from xmm2/m128 to packed BF16 data in xmm1 with writemask k1.
EVEX.256.F3.0F38.W0 72 /r VCVTNEPS2BF16 xmm1{k1}{z}, ymm2/m256/m32bcst A V/V AVX512VL AVX512_BF16 Convert packed single data from ymm2/m256 to packed BF16 data in xmm1 with writemask k1.
EVEX.512.F3.0F38.W0 72 /r VCVTNEPS2BF16 ymm1{k1}{z}, zmm2/m512/m32bcst A V/V AVX512F AVX512_BF16 Convert packed single data from zmm2/m512 to packed BF16 data in ymm1 with writemask k1.

Instruction Operand Encoding

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

Description

Converts one SIMD register of packed single data into a single register of packed BF16 data.

This instruction uses “Round to nearest (even)” rounding mode. Output denormals are always flushed to zero and input denormals are always treated as zero. MXCSR is not consulted nor updated.

As the instruction operand encoding table shows, the EVEX.vvvv field is not used for encoding an operand. EVEX.vvvv is reserved and must be 0b1111 otherwise instructions will #UD.

Operation

Define convert_fp32_to_bfloat16(x):
    IF x is zero or denormal:
        dest[15] := x[31] // sign preserving zero (denormal go to zero)
        dest[14:0] := 0
    ELSE IF x is infinity:
        dest[15:0] := x[31:16]
    ELSE IF x is NAN:
        dest[15:0] := x[31:16] // truncate and set MSB of the mantissa to force QNAN
        dest[6] := 1
    ELSE // normal number
        LSB := x[16]
        rounding_bias := 0x00007FFF + LSB
        temp[31:0] := x[31:0] + rounding_bias // integer add
        dest[15:0] := temp[31:16]
    RETURN dest

VCVTNEPS2BF16 dest, src

VL = (128, 256, 512)
KL = VL/16
origdest := dest
FOR i := 0 to KL/2-1:
    IF k1[ i ] or *no writemask*:
        IF src is memory and evex.b == 1:
            t := src.fp32[0]
        ELSE:
            t := src.fp32[ i ]
        dest.word[i] := convert_fp32_to_bfloat16(t)
    ELSE IF *zeroing*:
        dest.word[ i ] := 0
    ELSE: // Merge masking, dest element unchanged
        dest.word[ i ] := origdest.word[ i ]
DEST[MAXVL-1:VL/2] := 0

Intel C/C++ Compiler Intrinsic Equivalent

VCVTNEPS2BF16 __m128bh _mm_cvtneps_pbh (__m128);
VCVTNEPS2BF16 __m128bh _mm_mask_cvtneps_pbh (__m128bh, __mmask8, __m128);
VCVTNEPS2BF16 __m128bh _mm_maskz_cvtneps_pbh (__mmask8, __m128);
VCVTNEPS2BF16 __m128bh _mm256_cvtneps_pbh (__m256);
VCVTNEPS2BF16 __m128bh _mm256_mask_cvtneps_pbh (__m128bh, __mmask8, __m256);
VCVTNEPS2BF16 __m128bh _mm256_maskz_cvtneps_pbh (__mmask8, __m256);
VCVTNEPS2BF16 __m256bh _mm512_cvtneps_pbh (__m512);
VCVTNEPS2BF16 __m256bh _mm512_mask_cvtneps_pbh (__m256bh, __mmask16, __m512);
VCVTNEPS2BF16 __m256bh _mm512_maskz_cvtneps_pbh (__mmask16, __m512);

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Table 2-49, “Type E4 Class Exception Conditions”.