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VREDUCESS—Perform a Reduction Transformation on a Scalar Float32 Value

Opcode/Instruction Op /En 64/32 bit Mode Support CPUID Feature Flag Description

EVEX.NDS.LIG.66.0F3A.W0 57 /r /ib

VREDUCESS xmm1 {k1}{z}, xmm2, xmm3/m32{sae}, imm8

T1S V/V AVX512DQ Perform a reduction transformation on a scalar single-precision floating point value in xmm3/m32 by subtracting a number of fraction bits specified by the imm8 field. Also, upper single precision floating-point values (bits[127:32]) from xmm2 are copied to xmm1[127:32]. Stores the result in xmm1 register.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
T1S ModRM:reg (w) EVEX.vvvv (r) ModRM:r/m (r) NA


Perform a reduction transformation of the binary encoded single-precision FP value in the low dword element of the second source operand (the third operand) and store the reduced result in binary FP format to the low dword element of the destination operand (the first operand) under the writemask k1. Bits 127:32 of the destination operand are copied from respective dword elements of the first source operand (the second operand).

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

dest = src – (ROUND(2M*src))*2-M;

where “Round()” treats “src”, “2M”, and their product as binary FP numbers with normalized significand and bi-ased exponents.

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

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

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

Handling of special case of input values are listed in Table 5-21.


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 (cid:197) imm8[7:4]; // Number of fraction bits of the normalized significand to be subtracted
RC (cid:197) imm8[1:0];// Round Control for ROUND() operation
RC source (cid:197) imm[2];
SPE (cid:197) 0;// Suppress Precision Exception
TMP[31:0] (cid:197) 2-M *{ROUND(2M*SRC[31:0], SPE, RC_source, RC)}; // ROUND() treats SRC and 2M as standard binary FP values
TMP[31:0] (cid:197) 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
IF k1[0] or *no writemask*
    DEST[31:0] (cid:197) ReduceArgumentSP(SRC2[31:0], imm8[7:0])
    IF *merging-masking*
        ; merging-masking
        THEN *DEST[31:0] remains unchanged*
        ; zeroing-masking
        THEN DEST[31:0] = 0
DEST[127:32] (cid:197) SRC1[127:32]
DEST[MAX_VL-1:128] (cid:197) 0

Intel C/C++ Compiler Intrinsic Equivalent

VREDUCESS __m128 _mm_mask_reduce_ss( __m128 a, __m128 b, int imm, int sae)
VREDUCESS __m128 _mm_mask_reduce_ss(__m128 s, __mmask16 k, __m128 a, __m128 b, int imm, int sae)
VREDUCESS __m128 _mm_maskz_reduce_ss(__mmask16 k, __m128 a, __m128 b, int imm, int sae)

SIMD Floating-Point Exceptions

Invalid, Precision

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

Other Exceptions

See Exceptions Type E3.