Yes, that's a rather nasty cut & paste error I made.
But if the 31 is changed to a 15, is the code correct? I would think so. For
optimization I'd think that an assembly language version would make more sense,
and a few targets do that.
paul
> On Dec 4, 2018, at 5:51 PM, Stefan Kanthak <[email protected]> wrote:
>
> 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;
> }
