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Bug in divmodhi4(), plus poor inperformant code


Hi @ll,

libgcc's divmodhi4() function has an obvious bug; additionally
it shows rather poor inperformant code: two of the three conditions
tested in the first loop should clearly moved outside the loop!

divmodsi4() shows this inperformant code too!

regards
Stefan Kanthak

--- divmodhi4.c ---

unsigned short
__udivmodhi4(unsigned short num, unsigned short den, int modwanted)
{
  unsigned short bit = 1;
  unsigned short res = 0;

#ifdef BUGFIX
  if (den > num)
     return modwanted ? num : 0;
  if (den == num)
     return modwanted ? 0 : 1;
  while ((signed short) den >= 0)
#else // original, buggy and inperformant code
  while (den < num && bit && !(den & (1L<<31)))  // unsigned shorts are 16 bit!
#endif
    {
      den <<=1;
      bit <<=1;
    }
  while (bit)
    {
      if (num >= den)
        {
          num -= den;
          res |= bit;
        }
      bit >>=1;
      den >>=1;
    }
  if (modwanted) return num;
  return res;
}


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