diff options
author | Richard M. Stallman <[email protected]> | 2005-06-25 02:29:46 +0000 |
---|---|---|
committer | Richard M. Stallman <[email protected]> | 2005-06-25 02:29:46 +0000 |
commit | 32d4834cc6c76b53925edc5bf8db7079c8932413 (patch) | |
tree | bf57c8c25e9cb5eca06ef3c842c58a876f696a48 /lispref/numbers.texi | |
parent | 19cfc561f4ab393dcc5372b7e97d252009bec14e (diff) |
(Float Basics): Explain how to test for NaN, and printing the sign of NaNs.
Diffstat (limited to 'lispref/numbers.texi')
-rw-r--r-- | lispref/numbers.texi | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/lispref/numbers.texi b/lispref/numbers.texi index 776251e493..f7f88248ff 100644 --- a/lispref/numbers.texi +++ b/lispref/numbers.texi @@ -183,21 +183,26 @@ there is no correct answer. For example, @code{(/ 0.0 0.0)} returns a NaN. For practical purposes, there's no significant difference between different NaN values in Emacs Lisp, and there's no rule for precisely which NaN value should be used in a particular case, so Emacs Lisp -doesn't try to distinguish them. Here are the read syntaxes for -these special floating point values: +doesn't try to distinguish them (but it does report the sign, if you +print it). Here are the read syntaxes for these special floating +point values: @table @asis @item positive infinity @samp{1.0e+INF} @item negative infinity @samp{-1.0e+INF} -@item Not-a-number -@samp{0.0e+NaN}. +@item Not-a-number +@samp{0.0e+NaN} or @samp{-0.0e+NaN}. @end table - In addition, the value @code{-0.0} is distinguishable from ordinary -zero in @acronym{IEEE} floating point (although @code{equal} and -@code{=} consider them equal values). + To test whether a floating point value is a NaN, compare it with +itself using @code{=}. That returns @code{nil} for a NaN, and +@code{t} for any other floating point value. + + The value @code{-0.0} is distinguishable from ordinary zero in +@acronym{IEEE} floating point, but Emacs Lisp @code{equal} and +@code{=} consider them equal values. You can use @code{logb} to extract the binary exponent of a floating point number (or estimate the logarithm of an integer): |