Re: logbitp vs. logand+ash

[wfs@nicolas.ma.utexas.edu (Bill Schelter)]

Thank you very much for the bug report on logbitp.

Indeed there was an error in the bignum logbitp, [introduced
when the bignum types changed around akcl 530].   The error would
have occurred when the second arg was a bignum, and the index in words
was greater than the length of the bignum in words, but not more than
2 greater.   

Please add the lisp patch

(defun logbitp (p i) (/= (logand i (ash 1 p)) 0))

or in num_log.c replace the definition of big_bitp by

int
big_bitp(x, p)
object	x;
int	p;
{ GEN u = MP(x);
  int ans ;
  int i = p /32;
  if (signe(u) < 0)
    {  save_avma;
       u = complementi(u);
       restore_avma;
   }
  if (i < lgef(u) -MP_CODE_WORDS)
    { ans = ((MP_ITH_WORD(u,i,lgef(u))) & (1 << p%32));}
  else if (big_sign(x) < 0) ans = 1;
  else ans = 0;
  return ans;
}