rsqrtss
Reciprocal Square Root Scalar Single-Precision
Computes approximate reciprocal sqrt (1/sqrt(x)) of low float.
Pseudocode Operation
xmm1[0:31] ← 1.0 / sqrt(src[0:31]); xmm1[32:127] ← xmm1[32:127];Encoding
Operands
-
dest
128-bit XMM SIMD register -
src
128-bit XMM SIMD register or Memory operand
Related
More in SSE
Reference
Instruction Forms
| Opcode | Instruction | Op/En | 64/32-bit Mode | CPUID | Description |
|---|---|---|---|---|---|
| F3 0F 52 /r | RSQRTSS xmm1, xmm2/m32 | RM | V/V | SSE | Computes the approximate reciprocal of the square root of the low single precision floating-point value in xmm2/m32 and stores the results in xmm1. |
| VEX.LIG.F3.0F.WIG 52 /r | VRSQRTSS xmm1, xmm2, xmm3/m32 | AVX | RVM V/V Computes the approximate reciprocal of the square root of the low single precision floating-point value in xmm3/m32 and stores the results in xmm1. Also, upper single precision floating-point values (bits[127:32]) from xmm2 are copied to xmm1[127:32]. |
Description
Computes an approximate reciprocal of the square root of the low single precision floating-point value in the source operand (second operand) stores the single precision floating-point result in the destination operand. The source operand can be an XMM register or a 32-bit memory location. The destination operand is an XMM register. The three high-order doublewords of the destination operand remain unchanged. See Figure 10-6 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for an illustration of a scalar single precision floatingpoint operation. The relative error for this approximation is: |Relative Error| ≤ 1.5 ∗ 2-12 The RSQRTSS instruction is not affected by the rounding control bits in the MXCSR register. When a source value is a 0.0, an ∞ of the sign of the source value is returned. A denormal source value is treated as a 0.0 (of the same sign). When a source value is a negative value (other than -0.0), a floating-point indefinite is returned. When a source value is an SNaN or QNaN, the SNaN is converted to a QNaN or the source QNaN is returned. In 64-bit mode, using a REX prefix in the form of REX.R permits this instruction to access additional registers (XMM8-XMM15). 128-bit Legacy SSE version: The first source operand and the destination operand are the same. Bits (MAXVL1:32) of the corresponding YMM destination register remain unchanged. VEX.128 encoded version: Bits (MAXVL-1:128) of the destination YMM register are zeroed.
Operation
RSQRTSS (128-bit Legacy SSE Version) DEST[31:0] := APPROXIMATE(1/SQRT(SRC2[31:0])) DEST[MAXVL-1:32] (Unmodified) VRSQRTSS (VEX.128 Encoded Version) DEST[31:0] := APPROXIMATE(1/SQRT(SRC2[31:0])) DEST[127:32] := SRC1[127:32] DEST[MAXVL-1:128] := 0
Intel C/C++ Compiler Intrinsic Equivalent
RSQRTSS __m128 _mm_rsqrt_ss(__m128 a)