fre

Floating Reciprocal Estimate

fre FRT,FRB
fre. FRT,FRB

Estimates the reciprocal of a floating-point operand.

Details

An estimate of the reciprocal of the floating-point operand in register FRB is placed into register FRT. Unless the reciprocal would be a zero, an infinity, the result of a trap-disabled Overflow exception, or a QNaN, the estimate is correct to a precision of one part in 256 of the reciprocal of (FRB).

Pseudocode Operation

if 'fre' then
    FRT <- estimate(1 / (FRB))
else if 'fre.' then
    FRT <- estimate(1 / (FRB))
    CR1 <- result_class(FRT)

Programming Note

For the Floating-Point Estimate instructions, some implementations might implement a precision higher than the minimum architected precision.

Example

fre f1, f3

Encoding

Binary Layout
63
0
FRT
6
0
11
0
26
FRB
24
/
 
Format A-form
Opcode 0xFC000030
Extension Floating-Point
Registers Altered FPSCR (FPRF, FX, OX, UX, ZX, VXSNAN), CR1 (if Rc=1)

Operands

  • FRT
    Target
  • FRB
    Source