Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

Vol. 2B 4-267
INSTRUCTION SET REFERENCE, N-Z
RSQRTPS—Compute Reciprocals of Square Roots of Packed Single-
Precision Floating-Point Values
Description
Performs a SIMD computation of the approximate reciprocals of the square roots of
the four packed single-precision floating-point values in the source operand (second
operand) and stores the packed single-precision floating-point results in the destina-
tion operand. The source operand can be an XMM register or a 128-bit memory loca-
tion. The destination operand is an XMM register. See Figure 10-5 in the Intel
®
64
and IA-32 Architectures Software Developer’s Manual, Volume 1, for an illustration of
a SIMD single-precision floating-point operation.
The relative error for this approximation is:
|Relative Error|
≤ 1.5 ∗ 2
−12
The RSQRTPS 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).
Operation
DEST[31:0] ← APPROXIMATE(1.0/SQRT(SRC[31:0]));
DEST[63:32] ← APPROXIMATE(1.0/SQRT(SRC[63:32]));
DEST[95:64] ← APPROXIMATE(1.0/SQRT(SRC[95:64]));
DEST[127:96] ← APPROXIMATE(1.0/SQRT(SRC[127:96]));
Intel C/C++ Compiler Intrinsic Equivalent
RSQRTPS __m128 _mm_rsqrt_ps(__m128 a)
Opcode Instruction
64-Bit
Mode
Compat/
Leg Mode Description
0F 52 /r RSQRTPS xmm1,
xmm2/m128
Valid Valid Computes the approximate
reciprocals of the square roots of
the packed single-precision floating-
point values in xmm2/m128 and
stores the results in xmm1.