RSQRTPS — Compute Reciprocals of Square Roots of Packed Single-Precision Floating-Point Values

Instruction Operand Encoding ¶

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 destination operand. The source operand can be an XMM register or a 128-bit memory location. 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).

128-bit Legacy SSE version: The second source can be an XMM register or an 128-bit memory location. The destination is not distinct from the first source XMM register and the upper bits (MAXVL-1:128) of the corresponding YMM register destination are unmodified.

VEX.128 encoded version: the first source operand is an XMM register or 128-bit memory location. The destination operand is an XMM register. The upper bits (MAXVL-1:128) of the corresponding YMM register destination are zeroed.

VEX.256 encoded version: The first source operand is a YMM register. The second source operand can be a YMM register or a 256-bit memory location. The destination operand is a YMM register.

Note: In VEX-encoded versions, VEX.vvvv is reserved and must be 1111b, otherwise instructions will #UD.

Operation ¶

RSQRTPS (128-bit Legacy SSE version) ¶

DEST[31:0] ← APPROXIMATE(1/SQRT(SRC[31:0]))
DEST[63:32] ← APPROXIMATE(1/SQRT(SRC1[63:32]))
DEST[95:64] ← APPROXIMATE(1/SQRT(SRC1[95:64]))
DEST[127:96] ← APPROXIMATE(1/SQRT(SRC2[127:96]))
DEST[MAXVL-1:128] (Unmodified)

VRSQRTPS (VEX.128 encoded version) ¶

DEST[31:0] ← APPROXIMATE(1/SQRT(SRC[31:0]))
DEST[63:32] ← APPROXIMATE(1/SQRT(SRC1[63:32]))
DEST[95:64] ← APPROXIMATE(1/SQRT(SRC1[95:64]))
DEST[127:96] ← APPROXIMATE(1/SQRT(SRC2[127:96]))
DEST[MAXVL-1:128] ← 0

VRSQRTPS (VEX.256 encoded version) ¶

DEST[31:0] ← APPROXIMATE(1/SQRT(SRC[31:0]))
DEST[63:32] ← APPROXIMATE(1/SQRT(SRC1[63:32]))
DEST[95:64] ← APPROXIMATE(1/SQRT(SRC1[95:64]))
DEST[127:96] ← APPROXIMATE(1/SQRT(SRC2[127:96]))
DEST[159:128] ← APPROXIMATE(1/SQRT(SRC2[159:128]))
DEST[191:160] ← APPROXIMATE(1/SQRT(SRC2[191:160]))
DEST[223:192] ← APPROXIMATE(1/SQRT(SRC2[223:192]))
DEST[255:224] ← APPROXIMATE(1/SQRT(SRC2[255:224]))

Intel C/C++ Compiler Intrinsic Equivalent ¶

RSQRTPS: __m128 _mm_rsqrt_ps(__m128 a)

RSQRTPS: __m256 _mm256_rsqrt_ps (__m256 a);

SIMD Floating-Point Exceptions ¶

None.

Other Exceptions ¶

See Exceptions Type 4; additionally