# gmp 4.1 documentation improvement suggestions

**Torbjorn Granlund
**
tege@swox.com

*09 Dec 2002 20:15:09 +0100*

Vincent Lefevre <Vincent.Lefevre@loria.fr> writes:
> Page 8: "int mpfr_round_prec() Rounds x according to rnd with precision
> prec, which may be different from that of x. ... In both cases, the
> precision of x is changed to prec. The returned value is zero when the
> result is exact, positive when it is greater than the original value of
> x ..."
>
> Here I read "result is exact" to mean "the object x knew how many digits
> it had, and we have guessed it correctly". But of course this refers
> only to the value of precision stored in x, that may have little to do
> with the actual achieved precision of the approximation of some real
> number.
One should probably say "... when the result is equal to the original
value of x...".
Perhaps the docs should say something along these lines:
The return value of mpfr_round_prec is zero if changing the precision
of x didn't actually require any rounding, that is, the value of x
before and after the mpfr_round_prec are equal. Otherwise, the return
value is non-zero.
Note that as all results in mpfr are typically rounded, calling
mpfr_round_prec on a variable whose value is not to be ignored, will
imply that the variable is rounded twice. Such double rounding
typically leads to slightly less accurate results.
--
Torbjörn