RSQRTSS (Compute Reciprocal of Square Root of Scalar Single-Precision Floating-Point Value)
|Opcode*/Instruction||Op/En||64/32 bit Mode Support||CPUID Feature Flag||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.NDS.LIG.F3.0F.WIG 52 /r VRSQRTSS xmm1, xmm2, xmm3/m32||RVM||V/V||AVX||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].|
Instruction Operand Encoding
|Op/En||Operand 1||Operand 2||Operand 3||Operand 4|
|RM||ModRM:reg (w)||ModRM:r/m (r)||NA||NA|
|RVM||ModRM:reg (w)||VEX.vvvv (r)||ModRM:r/m (r)||NA|
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 floating-point 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 (VLMAX-1:32) of the corresponding YMM destination register remain unchanged.
VEX.128 encoded version: Bits (VLMAX-1:128) of the destination YMM register are zeroed.
RSQRTSS (128-bit Legacy SSE version)
DEST[31:0] ← APPROXIMATE(1/SQRT(SRC2[31:0])) DEST[VLMAX-1:32] (Unmodified)
VRSQRTSS (VEX.128 encoded version)
DEST[31:0] ← APPROXIMATE(1/SQRT(SRC2[31:0])) DEST[127:32] ← SRC1[127:32] DEST[VLMAX-1:128] ← 0
Intel C/C++ Compiler Intrinsic Equivalent
__m128 _mm_rsqrt_ss(__m128 a)
SIMD Floating-Point Exceptions
See Exceptions Type 5.