Re: [PATCH 06/25] Add struct scratch_buffer and its internal helper functions

[Paul Eggert <eggert at cs dot ucla dot edu>]

Thanks, this looks good.  One performance nit that I noticed this time 
around.  here:

On 04/06/2015 10:01 AM, Florian Weimer wrote:
> +  /* Avoid overflow check if both values are small. */
> +  if ((nelem | size) >> (sizeof (size_t) * CHAR_BIT / 2) != 0)
> +    {
> +      if (nelem != 0 && size > SIZE_MAX / nelem)
> +	{
> +	  /* Overflow.  Discard the old buffer, but it must remain
> +	     valid to free.  */
> +	  scratch_buffer_free (buffer);
> +	  scratch_buffer_init (buffer);
> +	  __set_errno (ENOMEM);
> +	  return false;
> +	}
> +    }
> +
> +  size_t new_length = nelem * size;

It's better to compute new_length first, before the overflow check, and 
then replace "size > SIZE_MAX / nelem" with "size != new_length / 
nelem".  This will avoid the need for having SIZE_MAX in the executable, 
which should shrink the code a tad.  Also, hardware integer division 
tends to run faster with smaller dividends, which would be the case if 
this change were made.