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VRSQRTPH - Compute Reciprocals of Square Roots of Packed FP16 Values

Opcode/ Instruction	Op/ En	64/32 bit Mode Support	CPUID Feature Flag	Description
EVEX.128.66.MAP6.W0 4E /r VRSQRTPH xmm1{k1}{z}, xmm2/ m128/m16bcst	A	V/V	AVX512-FP16 AVX512VL	Compute the approximate reciprocals of the square roots of packed FP16 values in xmm2/ m128/m16bcst and store the result in xmm1 subject to writemask k1.
EVEX.256.66.MAP6.W0 4E /r VRSQRTPH ymm1{k1}{z}, ymm2/ m256/m16bcst	A	V/V	AVX512-FP16 AVX512VL	Compute the approximate reciprocals of the square roots of packed FP16 values in ymm2/ m256/m16bcst and store the result in ymm1 subject to writemask k1.
EVEX.512.66.MAP6.W0 4E /r VRSQRTPH zmm1{k1}{z}, zmm2/ m512/m16bcst	A	V/V	AVX512-FP16	Compute the approximate reciprocals of the square roots of packed FP16 values in zmm2/ m512/m16bcst and store the result in zmm1 subject to writemask k1.

Instruction Operand Encoding

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

Description

This instruction performs a SIMD computation of the approximate reciprocals square-root of 8/16/32 packed FP16 floating-point values in the source operand (the second operand) and stores the packed FP16 floating-point results in the destination operand. The maximum relative error for this approximation is less than 2 - 11 + 2 - 14. For special cases, see Table 5-28.

The destination elements are updated according to the writemask.

Table 5-28. VRSQRTPH/VRSQRTSH Special Cases

X = 2 ^{- 2n}

Input value	Reset Value	Comments
Any denormal	Normal	Cannot generate overflow
X < 0	2n	Including - inf
X = - 0	- inf QNaN_Indefinite
X = +0	+inf
X = +inf
	+0

Operation

VRSQRTPH dest{k1}, src

VL = 128, 256 or 512
KL := VL/16
FOR i := 0 to KL-1:
   IF k1[i] or *no writemask*:
       IF SRC is memory and (EVEX.b = 1):
            tsrc := src.fp16[0]
       ELSE:
            tsrc := src.fp16[i]
       DEST.fp16[i] := APPROXIMATE(1.0 / SQRT(tsrc) )
   ELSE IF *zeroing*:
       DEST.fp16[i] := 0
   //else DEST.fp16[i] remains unchanged
DEST[MAXVL-1:VL] := 0 

Intel C/C++ Compiler Intrinsic Equivalent

VRSQRTPH __m128h _mm_mask_rsqrt_ph (__m128h src, __mmask8 k, __m128h a);
VRSQRTPH __m128h _mm_maskz_rsqrt_ph (__mmask8 k, __m128h a);
VRSQRTPH __m128h _mm_rsqrt_ph (__m128h a);
VRSQRTPH __m256h _mm256_mask_rsqrt_ph (__m256h src, __mmask16 k, __m256h a);
VRSQRTPH __m256h _mm256_maskz_rsqrt_ph (__mmask16 k, __m256h a);
VRSQRTPH __m256h _mm256_rsqrt_ph (__m256h a);
VRSQRTPH __m512h _mm512_mask_rsqrt_ph (__m512h src, __mmask32 k, __m512h a);
VRSQRTPH __m512h _mm512_maskz_rsqrt_ph (__mmask32 k, __m512h a);
VRSQRTPH __m512h _mm512_rsqrt_ph (__m512h a);

SIMD Floating-Point Exceptions

None.

Other Exceptions

EVEX-encoded instruction, see Table 2-49, "Type E4 Class Exception Conditions."