mpn_divexact_1 comments

[Mark Sofroniou]

I noticed a couple of minor issues in mpn_divexact_1 (dive1.c) that are
not in my own implementation, so I thought I'd pass them on.

If the quotient will be one word shorter than the dividend then set
the top word to zero:

   if ((divisor & 1) == 0)
     {
       if ((dst != src) && (src[size - 1] < divisor)) dst[size - 1] = 0;
...

This simplifies setting the length of the result in a caller function.

If the divisor is a power of two then skip the division code and
just shift or copy:

...

   /* divisor = 1, 2, 4, ... */
   if (divisor == 1)
     {
     if (shift)
       {
       mp_limb_t shifted_out;

       shifted_out = mpn_rshift (dst, src, size, shift);
       ASSERT (shifted_out == 0);
       }
     else
       {
       if (dst != src) mpn_copyi(dst, src, size);
       }
     return ;
     }

   binvert_limb (inverse, divisor);

...

Regards, Mark