Re: libpari precision handling changes

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

On Mon, Dec 04, 2023 at 12:10:41AM +0000, James Rickards wrote:
> Dear Bill,
> 
> In one of my programs I set a tolerance to be half of the precision (i.e. precision=2^-n, tolerance=2^(-n/2)) with:
> static GEN
> deftol(long prec)
> {
>   return real2n((BITS_IN_LONG >> 1)*(2 - prec), prec);
> }
> 
> You say that this change should not break most C programs, but I am correct in saying that this function is broken now?

Yes sorry. You can do that instead

return real2n( -nbits2prec(prec2nbits(prec)>>1), prec);

This should work with both definition of prec.

Generally, if you need to do arithmetic operation on the precision, do
nbits2prec ( ...  prec2nbits(prec) ... )

This way this does not depend on the internal representation.

Cheers,
Bill.