----------------------------
title : VEXP2PD (Intel x86/64 assembly instruction)
cat_title : VEXP2PD
ref_title : VEXP2PD
published : 2020-09-01
path : /X86-64 명령어 레퍼런스/V
publish_date: 2020-09-01
----------------------------


#@ VEXP2PD

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

```lec-info
아래 표를 해석하는 방법은 [x86-64 명령어 레퍼런스 읽는 법](/316) 글을 참조하시기 바랍니다.
```

|**Opcode/**\newline{}**Instruction**|**Op / **\newline{}**En**|**64/32 **\newline{}**bit Mode **\newline{}**Support**|**CPUID **\newline{}**Feature **\newline{}**Flag**|**Description**|
|------------------------------------|-------------------------|------------------------------------------------------|--------------------------------------------------|---------------|
|`EVEX.512.66.0F38.W1 C8 /r`\newline{}`VEXP2PD` zmm1 \tooltip{\{k1\}\{z\}}{쓰기 마스크 (write mask) 레지스터로 64 비트 k 레지스터로 k1 부터 k7 까지 사용 가능하다. 쓰기 마스크는 오직 EVEX 접두사가 있을 경우에만 사용 가능하다. 마스크 방식으로 마스크 되지 않는 부분의 값을 유지하는 병합 마스크 (merge mask) 가 있고, 해당 부분을 아예 0 으로 지워버리는 zeroing mask 방식이 있다. 어떤 식으로 마스크를 할 지는 EVEX.z 필드의 비트값에 따라 달라진다.} \tooltip{zmm2/m512/m64bcst}{ZMM 레지스터나 512 비트 메모리 데이터나, 64 비트 메모리 주소값에 불러온 벡터 데이터.} {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 
```info-verb
(KL, VL) = (8, 512)
FOR j <-  0 TO KL-1
    i <-  j * 64
    IF k1[j] OR *no writemask* THEN
                IF (EVEX.b = 1) AND (SRC *is memory*)
                      THEN DEST[i+63:i] <-  EXP2_23_DP(SRC[63:0])
                      ELSE DEST[i+63:i] <-  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] <-  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

```cpp
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.

