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Diffstat (limited to 'manual/stdio.texi')
| -rw-r--r-- | manual/stdio.texi | 55 |
1 files changed, 45 insertions, 10 deletions
diff --git a/manual/stdio.texi b/manual/stdio.texi index e922fd17d8..04c635b054 100644 --- a/manual/stdio.texi +++ b/manual/stdio.texi @@ -1007,6 +1007,12 @@ whichever is more appropriate for its magnitude. @samp{%g} uses lower-case letters and @samp{%G} uses upper-case. @xref{Floating-Point Conversions}, for details. +@item @samp{%a}, @samp{%A} +Print a floating-point number in a hexadecimal fractional notation which +the exponent to base 2 represented in decimal digits. @samp{%a} uses +lower-case letters and @samp{%A} uses upper-case. @xref{Floating-Point +Conversions}, for details. + @item @samp{%c} Print a single character. @xref{Other Output Conversions}. @@ -1194,6 +1200,34 @@ than -4 or greater than or equal to the precision; otherwise they use the of the result and a decimal-point character appears only if it is followed by a digit. +The @samp{%a} and @samp{%A} conversions are meant for representing +floating-point number exactly in textual form so that they can be +exchanged as texts between different programs and/or machines. The +numbers are represented is the form +@w{[@code{-}]@code{0x}@var{h}@code{.}@var{hhh}@code{p}[@code{+}|@code{-}]@var{dd}}. +At the left of the decimal-point character exactly one digit is print. +This character is only @code{0} is the number is denormalized. +Otherwise the value is unspecifed; it is implemention dependent how many +bits are used. The number of hexadecimal digits on the right side of +the decimal-point character is equal to the precision. If the precision +is zero it is determined to be large enough to provide an exact +representation of the number (or it is large enough to distinguish two +adjacent values if the @code{FLT_RADIX} is not a power of 2, +@pxref{Floating Point Parameters}) For the @samp{%a} conversion +lower-case characters are used to represent the hexadecimal number and +the prefix and exponent sign are printed as @code{0x} and @code{p} +respectively. Otherwise upper-case characters are used and @code{0X} +and @code{P} are used for the representation of prefix and exponent +string. The exponent to the base of two is printed as a decimal number +using at least one digit but at most as many digits as necessary to +represent the value exactly. + +If the value to be printed represents infinity or a NaN, the output is +@w{[@code{-}]@code{inf}} or @code{nan} respectively if the conversion +specifier is @samp{%a}, @samp{%e}, @samp{%f}, or @samp{%g} and it is +@w{[@code{-}]@code{INF}} or @code{NAN} respectively if the conversion is +@samp{%A}, @samp{%E}, or @samp{%G}. + The following flags can be used to modify the behavior: @comment We use @asis instead of @samp so we can have ` ' as an item. @@ -1255,21 +1289,22 @@ floating-point conversions. All of the numbers were printed using this template string: @smallexample -"|%12.4f|%12.4e|%12.4g|\n" +"|%13.4a|%13.4f|%13.4e|%13.4g|\n" @end smallexample Here is the output: @smallexample -| 0.0000| 0.0000e+00| 0| -| 1.0000| 1.0000e+00| 1| -| -1.0000| -1.0000e+00| -1| -| 100.0000| 1.0000e+02| 100| -| 1000.0000| 1.0000e+03| 1000| -| 10000.0000| 1.0000e+04| 1e+04| -| 12345.0000| 1.2345e+04| 1.234e+04| -| 100000.0000| 1.0000e+05| 1e+05| -| 123456.0000| 1.2346e+05| 1.234e+05| +| 0x0.0000p+0| 0.0000| 0.0000e+00| 0| +| 0x1.0000p-1| 0.5000| 5.0000e-01| 0.5| +| 0x1.0000p+0| 1.0000| 1.0000e+00| 1| +| -0x1.0000p+0| -1.0000| -1.0000e+00| -1| +| 0x1.9000p+6| 100.0000| 1.0000e+02| 100| +| 0x1.f400p+9| 1000.0000| 1.0000e+03| 1000| +| 0x1.3880p+13| 10000.0000| 1.0000e+04| 1e+04| +| 0x1.81c8p+13| 12345.0000| 1.2345e+04| 1.234e+04| +| 0x1.86a0p+16| 100000.0000| 1.0000e+05| 1e+05| +| 0x1.e240p+16| 123456.0000| 1.2346e+05| 1.235e+05| @end smallexample Notice how the @samp{%g} conversion drops trailing zeros. |