[Octave-bug-tracker] [bug #61319] idivide fails to distinguish between ceil and floor for inputs close to perfect squares

[Arun Giridhar]

Follow-up Comment #7, bug #61319 (project octave):

This is where I am now after some testing. The tricky ones are the cases near
intmin, intmax, and the unsigned cases. I think it might be better to split
signed and unsigned types separately.


  if (strcmp (op, "fix"))
    ii = (y > 0) & (x > 0) | (y < 0) & (x < 0);      ## ii == same signs for x
and y
    z(ii) = (x(ii) - mod (x(ii), y(ii))) ./ y(ii);   ## same as floor for
positive
    z(~ii) = (-x(~ii) - mod (-x(~ii), y(~ii))) ./ y(~ii);   ## opposite sign
for negative
    ## FIXME: unsigned types will break if user is mixing unsigned and
signed.
  elseif (strcmp (op, "round"))
    z = x ./ y;
  elseif (strcmp (op, "floor"))
    z = (x - mod (x, y)) ./ y;   ## FIXME: underflow near intmin?
  elseif (strcmp (op, "ceil"))
    r = mod (x, y);
    z = (x - r) ./ y;            ## FIXME: underflow near intmin?
    z(r>0) += 1;
  else
    error ('idivide: unrecognized rounding type "%s"', op);
  endif


Hopefully there's a better way to do it.

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