[doc/mpfr.texi] Formatted output functions (mpfr_*printf): completed

the specification concerning the precision (this was needed because
the conversion specifier 'b' does not exist in C).

git-svn-id: https://scm.gforge.inria.fr/anonscm/svn/mpfr/trunk@14517 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 17 insertions, 6 deletions

diff --git a/doc/mpfr.texi b/doc/mpfr.texi
index b7e97425e..631e55ee8 100644
--- a/doc/mpfr.texi
+++ b/doc/mpfr.texi
@@ -2894,8 +2894,13 @@ for @samp{a}, @samp{b}, @samp{e}, @samp{f}, and @samp{g} specifiers and
 
 The @code{mpfr_t} number is rounded to the given precision in the direction
 specified by the rounding mode (see below if the precision is missing).
+Similarly to the native C types, the precision is the number of digits
+output after the decimal point, except for the @samp{g} and @samp{G}
+conversion specifiers, where it is the number of significant digits
+(but trailing zeros of the fractional part are not output by default),
+or 1 if the precision is zero.
 If the precision is zero with rounding to nearest mode and one of the
-following @samp{conv} specifiers: @samp{a}, @samp{A}, @samp{b}, @samp{e},
+following conversion specifiers: @samp{a}, @samp{A}, @samp{b}, @samp{e},
 @samp{E}, tie case is rounded to even when it lies between two consecutive
 values at the
 wanted precision which have the same exponent, otherwise, it is rounded away
@@ -2907,9 +2912,14 @@ uses the @samp{e} (resp.@: @samp{E}) style.
 If the precision is set to a value greater than the maximum value for an
 @code{int}, it will be silently reduced down to @code{INT_MAX}.
 
-If the precision is missing with @samp{conv} specifier @samp{e} and @samp{E}
-(as in @code{%Re}), the chosen precision (i.e., the number of digits to be
-displayed after the initial digit and the decimal point) is
+If the precision is missing, it is chosen as follows, depending on the
+conversion specifier.
+@itemize @bullet
+@item With @samp{a}, @samp{A}, and @samp{b}, it is chosen to have
+an exact representation with no trailing zeros.
+@c Avoid saying "minimum" as this could be confusing with the different
+@c possible choices for a/A.
+@item With @samp{e} and @samp{E}, it is
 @ifnottex
 ceil(@var{p}*log(2)/log(@var{10})),
 @end ifnottex
@@ -2920,8 +2930,9 @@ where @var{p} is the precision of the input variable, matching the choice
 done for @code{mpfr_get_str}; thus, if rounding to nearest is used,
 outputting the value with a missing precision and reading it back will
 yield the original value.
-The chosen precision for a missing precision with @samp{conv}
-specifiers @samp{f}, @samp{F}, @samp{g}, and @samp{G} is 6.
+@item With @samp{f}, @samp{F}, @samp{g}, and @samp{G}, it is 6.
+@end itemize
+
 @c For the record, concerning the choice for 'e'/'E':
 @c   https://sympa.inria.fr/sympa/arc/mpfr/2019-12/msg00000.html
 @c   https://sympa.inria.fr/sympa/arc/mpfr/2020-01/msg00000.html