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VEXP2PD—Approximation to the Exponential 2^x of Packed Double-Precision Floating-Point Values with Less Than 2^-23 Relative Error

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

EVEX.512.66.0F38.W1 C8 /r

VEXP2PD zmm1 {k1}{z}, zmm2/m512/m64bcst {sae}

 FV V/V AVX512ER Computes approximations to the exponential 2^x (with less than 2^-23 of maximum relative error) of the packed double-precision floating-point values from zmm2/m512/m64bcst and stores the floating-point result in zmm1with writemask k1.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
FV ModRM:reg (r, w) ModRM:r/m (r) NA NA

Description

Computes the approximate base-2 exponential evaluation of the double-precision floating-point values in the source operand (the second operand) and stores the results to the destination operand (the first operand) using the writemask k1. The approximate base-2 exponential is evaluated with less than 2^-23 of relative error.

Denormal input values are treated as zeros and do not signal #DE, irrespective of MXCSR.DAZ. Denormal results are flushed to zeros and do not signal #UE, irrespective of MXCSR.FZ.

The source operand is a ZMM register, a 512-bit memory location or a 512-bit vector broadcasted from a 64-bit memory location. The destination operand is a ZMM register, conditionally updated using writemask k1.

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

A numerically exact implementation of VEXP2xx can be found at https://software.intel.com/en-us/articles/refer-ence-implementations-for-IA-approximation-instructions-vrcp14-vrsqrt14-vrcp28-vrsqrt28-vexp2.

Operation


VEXP2PD

(KL, VL) = (8, 512)
FOR j (cid:197) 0 TO KL-1
    i (cid:197) j * 64
    IF k1[j] OR *no writemask* THEN
        IF (EVEX.b = 1) AND (SRC *is memory*)
            THEN DEST[i+63:i] (cid:197) EXP2_23_DP(SRC[63:0])
            ELSE DEST[i+63:i] (cid:197) EXP2_23_DP(SRC[i+63:i])
        FI;
        ELSE
        IF *merging-masking*
            ; merging-masking
            THEN *DEST[i+63:i] remains unchanged*
            ELSE
            ; zeroing-masking
            DEST[i+63:i] (cid:197) 0
        FI;
    FI;
ENDFOR;

Table 5-4. Special Values Behavior





Source Input
Result
Comments



NaN
QNaN(src)
If (SRC = SNaN) then #I



+∞
+∞




+/-0
1.0f
Exact result



-∞
+0.0f




Integral value N
2^ (N)
Exact result




Intel C/C++ Compiler Intrinsic Equivalent


VEXP2PD __m512d _mm512_exp2a23_round_pd (__m512d a, int sae);
VEXP2PD __m512d _mm512_mask_exp2a23_round_pd (__m512d a, __mmask8 m, __m512d b, int sae);
VEXP2PD __m512d _mm512_maskz_exp2a23_round_pd ( __mmask8 m, __m512d b, int sae);



SIMD Floating-Point Exceptions


Invalid (if SNaN input), Overflow


Other Exceptions


See Exceptions Type E2.