Small toom43 cleanup

Torbjorn Granlund tg at
Wed Oct 21 08:44:49 CEST 2009

bodrato at writes:

  > mp_size_t is a signed type, for various reasons.  size_t is an unsigned
  > type.  Unsigned division by constants is a few cycles faster.
  Ok, but in all cases we have
  mp_size_t bn;
  mp_size_t n = (bn-1) / (cast type) 3;
  Does the compiler know that (bn-1) is unsigned positive? I do not think so...

I don't understand what you mean by "unsigned" here.
Surely the compiler does not know that bn-1 >= 0.

  Will it compile a signed or an unsigned division?

Unsigned, if it is a standards conforming C compiler.

  Maybe it is better to cast the other side:
  mp_size_t n = ((unsigned type)bn-1) / 3;
That should be equivalent.

  and let the compiler decide the best type for the small constants 1 and 3 ?

The type of 3 is "signed int".


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