VREDUCESS - Perform a Reduction Transformation on a Scalar Float32 Value

Opcode/ Instruction

Op / En

64/32 bit Mode Support

CPUID Feature Flag

Description

EVEX.LLIG.66.0F3A.W0 57 /r /ib VREDUCESS xmm1 {k1}{z}, xmm2, xmm3/m32{sae}, imm8

A

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

Tuple Type

Operand 1

Operand 2

Operand 3

Operand 4

A

Tuple1 Scalar

ModRM:reg (w)

EVEX.vvvv (r)

ModRM:r/m (r)

N/A

Description

Perform a reduction transformation of the binary encoded single-precision floating-point value in the low dword element of the second source operand (the third operand) and store the reduced result in binary floating-point 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 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(2M*src))*2-M; where "Round()" treats "src", "2M", 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= 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 5-19.

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(2M*SRC[31:0], SPE, RC_source, RC)}; // ROUND() treats SRC and 2M 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
}

VREDUCESS 

IF k1[0] or *no writemask*
   THEN    DEST[31:0] := ReduceArgumentSP(SRC2[31:0], imm8[7:0])
   ELSE 
       IF *merging-masking*                ; merging-masking
            THEN *DEST[31:0] remains unchanged*
            ELSE                            ; zeroing-masking
                THEN DEST[31:0] = 0
       FI;
FI;
DEST[127:32] := SRC1[127:32]
DEST[MAXVL-1:128] := 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 Table 2-47, "Type E3 Class Exception Conditions."