RCPSS

Compute Reciprocal of Scalar Single Precision Floating-Point Values

stableVMJITAOTinstruction

Encodings

Operand encoding

Each mode is a value of the Op/En column above. It says which field of the encoded instruction carries each operand, in the order they are written, and whether the instruction reads it, writes it or both.

Measured cost

Description#

Computes of an approximate reciprocal of the low single precision floating-point value in the source operand (second operand) and 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(R) 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 RCPSS 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 (see Section 4.9.1.5, "Numeric Underflow Exception (#U)" in Intel(R) 64 and IA-32 Architectures Software Developer's Manual, Volume 1) are always flushed to 0.0, with the sign of the operand. (Input values greater than or equal to |1.11111111110100000000000B2125| 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 first source operand and the destination operand are the same. Bits (MAXVL- 1:32) of the corresponding YMM destination register remain unchanged.

VEX.128 encoded version: Bits (MAXVL-1:128) of the destination YMM register are zeroed.

Operation#

RCPSS (128-bit Legacy SSE Version)
DEST[31:0] := APPROXIMATE(1/SRC[31:0])
DEST[MAXVL-1:32] (Unmodified)


VRCPSS (VEX.128 Encoded Version)
DEST[31:0] := APPROXIMATE(1/SRC2[31:0])
DEST[127:32] := SRC1[127:32]
DEST[MAXVL-1:128] := 0

Intel C/C++ compiler intrinsics#

RCPSS __m128 _mm_rcp_ss(__m128 a);

SIMD Floating-Point Exceptions#

None.

Other Exceptions#

See Table 2-22, "Type 5 Class Exception Conditions."

Sources

• This instruction in the Intel manual
• Latency and throughput per microarchitecture