public BigDecimal pow(BigDecimal rhs,MathContext set)
{
int n;
BigDecimal lhs;
int reqdig;
int workdigits=0;
int L=0;
MathContext workset;
BigDecimal res;
bool seenbit;
int i=0;
if (set.lostDigits)
checkdigits(rhs,set.digits);
n=rhs.intcheck(MinArg,MaxArg); // check RHS by the rules
lhs=this; // clarified name
reqdig=set.digits; // local copy (heavily used)
if (reqdig==0)
{
if (rhs.ind==isneg)
throw new System.ArithmeticException("Negative power:"+" "+rhs.ToString());
workdigits=0;
}
else
{/* non-0 digits */
if ((rhs.mant.Length+rhs.exp)>reqdig)
throw new System.ArithmeticException("Too many digits:"+" "+rhs.ToString());
/* Round the lhs to DIGITS if need be */
if (lhs.mant.Length>reqdig)
lhs=clone(lhs).round(set);
/* L for precision calculation [see ANSI X3.274-1996] */
L=rhs.mant.Length+rhs.exp; // length without decimal zeros/exp
workdigits=(reqdig+L)+1; // calculate the working DIGITS
}
workset=new MathContext(workdigits,set.form,false,set.roundingMode);
res=ONE; // accumulator
if (n==0)
return res; // x**0 == 1
if (n<0)
n=(int)-n; // [rhs.ind records the sign]
seenbit=false; // set once we've seen a 1-bit
for(i=1;;i++){ // for each bit [top bit ignored]
n=n+n; // shift left 1 bit
if (n<0)
{ // top bit is set
seenbit=true; // OK, we're off
res=res.multiply(lhs,workset); // acc=acc*x
}
if (i==31)
break; // that was the last bit
if ((!seenbit))
continue; // we don't have to square 1
res=res.multiply(res,workset); // acc=acc*acc [square]
}
if (rhs.ind<0) // was a **-n [hence digits>0]
res=ONE.divide(res,workset); // .. so acc=1/acc
return res.finish(set,true); // round and strip [original digits]
}
