xvrsqrtedp

Vector Reciprocal Square Root Estimate Double-Precision

xvrsqrtedp XT,XB

Estimates the reciprocal square root of double-precision floating-point values in vector registers.

Encoding

Binary Layout

202

30 31

Format XX2-form

Opcode 0xF0000328

Extension VSX

Operands

XT
Target Vector Register
XB
Source Vector Register

Example

xvrsqrtedp vs1, vs3

Registers Altered

FPSCR (FX, ZX, VXSNAN, VXSQRT)

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

This instruction estimates the reciprocal square root of each element in a double-precision floating-point vector and stores the result in another vector register. The estimate has a relative error no greater than one part in 16384 of the reciprocal of the square root of the source value.

Operation

if MSR.VSX=0 then VSX_Unavailable()

ex_flag ←0b0

do i = 0 to 1
    reset_xflags()
    src ←bfp_CONVERT_FROM_BFP64(VSR[32×BX+B].dword[i])
    v   ←bfp_RECIPROCAL_SQUARE_ROOT_ESTIMATE(src)
    rnd ←bfp_ROUND_TO_BFP64(0b0,FPSCR.RN,v)
    vresult.dword[i] ←bfp64_CONVERT_FROM_BFP(rnd)
    if vxsqrt_flag=1 then SetFX(FPSCR.VXSQRT)
    if zx_flag=1 then SetFX(FPSCR.ZX)
    if vxsnan_flag=1 then SetFX(FPSCR.VXSNAN) if vxsnan_flag=1 then SetFX(FPSCR.VXSNAN)
end

if ex_flag=0 then VSR[32×TX+T] ←vresult

Programming Note

The xvrsqrtedp instruction is used to estimate the reciprocal square root of each element in a double-precision floating-point vector. It requires VSX (Vector Scalar Extensions) to be enabled, otherwise, it will raise an exception. The result has a relative error no greater than one part in 16384. Be cautious with special values like NaNs or zeros, as they can trigger exceptions and set specific flags in the FPSCR register.