gmp 4.1 documentation improvement suggestions
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
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.