RCPPS—Compute Reciprocals of Packed Single-Precision Floating-Point Values

Instruction Operand Encoding

Description

Performs a SIMD computation of the approximate reciprocals of the four packed single-precision floating-point values in the source operand (second operand) 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 RCPPS 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). Tiny results are always flushed to 0.0, with the sign of the operand. (Input values greater than or equal to |1.11111111110100000000000B∗2¹²⁵| are guaranteed to not produce tiny results; input values less than or equal to |1.00000000000110000000001B*2¹²⁶| are guaranteed to produce tiny results, which are in turn flushed to 0.0; and input values in between this range may or may not produce tiny results, depending on the implementation.) 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 desti-nation is not distinct from the first source XMM register and the upper bits (VLMAX-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 (VLMAX-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

RCPPS (128-bit Legacy SSE version)

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

VRCPPS (VEX.128 encoded version)

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

VRCPPS (VEX.256 encoded version)

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

Intel C/C++ Compiler Intrinsic Equivalent

RCCPS:

__m128 _mm_rcp_ps(__m128 a)

RCPPS:

__m256 _mm256_rcp_ps (__m256 a);

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type 4; additionally