xsrsqrtedp

Double-Precision XX2-form Scalar Reciprocal Square Root Estimate

xsrsqrtedp XT,XB

Estimates the reciprocal square root of a double-precision floating-point value.

Details

The instruction estimates the reciprocal square root of the double-precision floating-point value in doubleword element 0 of VSR[XB] and places the result into doubleword element 0 of VSR[XT]. Doubleword element 1 of VSR[XT] is set to 0.

Pseudocode Operation

if MSR.VSX=0 then VSX_Unavailable()
reset_xflags()
src ← bfp_CONVERT_FROM_BFP64(VSR[32×BX+B].dword[0])
v ← bfp_RECIPROCAL_SQUARE_ROOT_ESTIMATE(src)
rnd ← bfp_ROUND_TO_BFP64(0b0, FPSCR.RN, v)
result ← bfp64_CONVERT_FROM_BFP(rnd)
if vxsnan_flag=1 then SetFX(FPSCR.VXSNAN)
if vxsqrt_flag=1 then SetFX(FPSCR.VXSQRT)
if zx_flag=1 then SetFX(FPSCR.ZX)
vx_flag ← vxsnan_flag | vxsqrt_flag
vex_flag ← FPSCR.VE & vx_flag
zex_flag ← FPSCR.ZE & zx_flag
if vex_flag=0 & zex_flag=0 then do
    VSR[32×TX+T].dword[0] ← result
    VSR[32×TX+T].dword[1] ← 0x0000_0000_0000_0000
    FPSCR.FPRF ← fprf_CLASS_BFP64(result)
    FPSCR.FR ← 0bU
    FPSCR.FI ← 0bU
end

Programming Note

Previous versions of the architecture allowed the contents of doubleword 1 of the result register to be undefined. However, all processors that support this instruction write 0s into doubleword 1 of the result register.

Example

xsrsqrtedp vs1, vs3

Encoding

Binary Layout
18
0
T
6
B
11
74
16
 
Format XX2-form
Opcode 0xF0000128
Extension VSX
Registers Altered FPSCR (FPRF, FX, VXSNAN, FR, FI)

Operands

  • XT
    Target Vector-Scalar Register
  • XB
    Source Vector-Scalar Register