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Diffstat (limited to 'doc/gawktexi.in')
| -rw-r--r-- | doc/gawktexi.in | 27 |
1 files changed, 26 insertions, 1 deletions
diff --git a/doc/gawktexi.in b/doc/gawktexi.in index a9a670db..8c4cb893 100644 --- a/doc/gawktexi.in +++ b/doc/gawktexi.in @@ -4898,6 +4898,12 @@ function names added by @command{gawk} after the code was written. Standard @command{awk} built-in functions, such as @code{sin()} or @code{substr()} are @emph{not} shadowed in this way. +You can use a @samp{P} modifier for the @code{printf()} floating-point +format control letters to use the underlying C library's result for +NaN and Infinity values, instead of the special values @command{gawk} +usually produces, as described in @ref{POSIX Floating Point Problems}. +This is mainly useful for the included unit tests. + @end ignore @node Invoking Summary @@ -9311,6 +9317,17 @@ values or do something else entirely. @value{DARKCORNER} @end quotation +@quotation NOTE +The IEEE 754 standard for floating-point arithmetic allows for special +values that represent ``infinity'' (positive and negative) and values +that are ``not a number'' (NaN). + +Input and output of these values occurs as text strings. This is +somewhat problematic for the @command{awk} language, which predates +the IEEE standard. Further details are provided in +@ref{POSIX Floating Point Problems}; please see there. +@end quotation + @node Format Modifiers @subsection Modifiers for @code{printf} Formats @@ -31601,7 +31618,7 @@ which is @emph{not} recommended). For example: $ @kbd{echo nanny | gawk '@{ print $1 + 0 @}'} @print{} 0 $ @kbd{echo +nan | gawk '@{ print $1 + 0 @}'} -@print{} nan +@print{} +nan $ @kbd{echo 0xDeadBeef | gawk '@{ print $1 + 0 @}'} @print{} 0 @end example @@ -31610,6 +31627,14 @@ $ @kbd{echo 0xDeadBeef | gawk '@{ print $1 + 0 @}'} Thus, @samp{+nan} and @samp{+NaN} are the same. @end itemize +Besides handling imput, @command{gawk} also needs to print ``correct'' values on +output when a value is either NaN or infinity. Starting with version 4.2.2, +for such values @command{gawk} prints one of the four strings +just described: @samp{+inf}, @samp{-inf}, @samp{+nan}, or @samp{-nan}. +Similarly, in POSIX mode, @command{gawk} prints the result of +the system's C @code{printf()} function using the @code{%g} format string +for the value, whatever that may be. + @node Floating point summary @section Summary |