x86doc › VREDUCEPS - Perform Reduction Transformation on Packed Float32 Values

VREDUCEPS—Perform Reduction Transformation on Packed Float32 Values

Opcode/Instruction	Op /En	64/32 bit Mode Support	CPUID Feature Flag	Description
EVEX.128.66.0F3A.W0 56 /r ib VREDUCEPS xmm1 {k1}{z}, xmm2/m128/m32bcst, imm8	A	V/V	AVX512VL AVX512DQ	Perform reduction transformation on packed single-precision floating-point values in xmm2/m128/m32bcst by subtracting a number of fraction bits specified by the imm8 field. Stores the result in xmm1 register under writemask k1.
EVEX.256.66.0F3A.W0 56 /r ib VREDUCEPS ymm1 {k1}{z}, ymm2/m256/m32bcst, imm8	A	V/V	AVX512VL AVX512DQ	Perform reduction transformation on packed single-precision floating-point values in ymm2/m256/m32bcst by subtracting a number of fraction bits specified by the imm8 field. Stores the result in ymm1 register under writemask k1.
EVEX.512.66.0F3A.W0 56 /r ib VREDUCEPS zmm1 {k1}{z}, zmm2/m512/m32bcst{sae}, imm8	A	V/V	AVX512DQ	Perform reduction transformation on packed single-precision floating-point values in zmm2/m512/m32bcst by subtracting a number of fraction bits specified by the imm8 field. Stores the result in zmm1 register under writemask k1.

Instruction Operand Encoding

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

Description

Perform reduction transformation of the packed binary encoded single-precision floating-point values in the source operand (the second operand) and store the reduced results in binary floating-point format to the destination operand (the first operand) under the writemask k1.

The reduction transformation subtracts the integer part and the leading M fractional bits from the binary floating-point source value, where M is a unsigned integer specified by imm8[7:4], see Figure 5-28. Specifically, the reduc-tion transformation can be expressed as:

dest = src – (ROUND(2^M*src))*2^-M;

where “Round()” treats “src”, “2^M”, and their product as binary floating-point numbers with normalized signifi-cand and biased exponents.

The magnitude of the reduced result can be expressed by considering src= 2^p*man2, where ‘man2’ is the normalized significand and ‘p’ is the unbiased exponent

Then if RC = RNE: 0<=|Reduced Result|<=2^p-M-1

Then if RC ≠ RNE: 0<=|Reduced Result|<2^p-M

This instruction might end up with a precision exception set. However, in case of SPE set (i.e., Suppress Precision Exception, which is imm8[3]=1), no precision exception is reported.

EVEX.vvvv is reserved and must be 1111b otherwise instructions will #UD.

Handling of special case of input values are listed in Table 5-19.

Operation

ReduceArgumentSP(SRC[31:0], imm8[7:0])

{

// Check for NaN

IF (SRC [31:0] = NAN) THEN

RETURN (Convert SRC[31:0] to QNaN); FI

M := imm8[7:4]; // Number of fraction bits of the normalized significand to be subtracted

RC := imm8[1:0];// Round Control for ROUND() operation

RC source := imm[2];

SPE := imm[3];// Suppress Precision Exception

TMP[31:0] := 2^-M *{ROUND(2^M*SRC[31:0], SPE, RC_source, RC)}; // ROUND() treats SRC and 2^M as standard binary FP values

TMP[31:0] := SRC[31:0] – TMP[31:0]; // subtraction under the same RC,SPE controls

RETURN TMP[31:0]; // binary encoded FP with biased exponent and normalized significand

}

VREDUCEPS

(KL, VL) = (4, 128), (8, 256), (16, 512)

FOR j := 0 TO KL-1

i := j * 32

IF k1[j] OR *no writemask* THEN

IF (EVEX.b == 1) AND (SRC *is memory*)

THEN DEST[i+31:i] := ReduceArgumentSP(SRC[31:0], imm8[7:0]);

ELSE DEST[i+31:i] := ReduceArgumentSP(SRC[i+31:i], imm8[7:0]);

FI;

ELSE

IF *merging-masking*

; merging-masking

THEN *DEST[i+31:i] remains unchanged*

ELSE

; zeroing-masking

DEST[i+31:i] = 0

FI;

FI;

ENDFOR;

DEST[MAXVL-1:VL] := 0

Intel C/C++ Compiler Intrinsic Equivalent

VREDUCEPS __m512 _mm512_mask_reduce_ps( __m512 a, int imm, int sae)

VREDUCEPS __m512 _mm512_mask_reduce_ps(__m512 s, __mmask16 k, __m512 a, int imm, int sae)

VREDUCEPS __m512 _mm512_maskz_reduce_ps(__mmask16 k, __m512 a, int imm, int sae)

VREDUCEPS __m256 _mm256_mask_reduce_ps( __m256 a, int imm)

VREDUCEPS __m256 _mm256_mask_reduce_ps(__m256 s, __mmask8 k, __m256 a, int imm)

VREDUCEPS __m256 _mm256_maskz_reduce_ps(__mmask8 k, __m256 a, int imm)

VREDUCEPS __m128 _mm_mask_reduce_ps( __m128 a, int imm)

VREDUCEPS __m128 _mm_mask_reduce_ps(__m128 s, __mmask8 k, __m128 a, int imm)

VREDUCEPS __m128 _mm_maskz_reduce_ps(__mmask8 k, __m128 a, int imm)

SIMD Floating-Point Exceptions

Invalid, Precision.

If SPE is enabled, precision exception is not reported (regardless of MXCSR exception mask).

Other Exceptions

See Table 2-46, “Type E2 Class Exception Conditions”; additionally:

#UD	If EVEX.vvvv != 1111B.