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revision 1.34 by rms, Mon Feb 14 10:19:36 2005 UTC revision 1.35 by rms, Sat Jun 25 02:29:46 2005 UTC
# Line 183  there is no correct answer.  For example Line 183  there is no correct answer.  For example
183  NaN.  For practical purposes, there's no significant difference between  NaN.  For practical purposes, there's no significant difference between
184  different NaN values in Emacs Lisp, and there's no rule for precisely  different NaN values in Emacs Lisp, and there's no rule for precisely
185  which NaN value should be used in a particular case, so Emacs Lisp  which NaN value should be used in a particular case, so Emacs Lisp
186  doesn't try to distinguish them.  Here are the read syntaxes for  doesn't try to distinguish them (but it does report the sign, if you
187  these special floating point values:  print it).  Here are the read syntaxes for these special floating
188    point values:
189    
190  @table @asis  @table @asis
191  @item positive infinity  @item positive infinity
192  @samp{1.0e+INF}  @samp{1.0e+INF}
193  @item negative infinity  @item negative infinity
194  @samp{-1.0e+INF}  @samp{-1.0e+INF}
195  @item Not-a-number  @item Not-a-number
196  @samp{0.0e+NaN}.  @samp{0.0e+NaN} or @samp{-0.0e+NaN}.
197  @end table  @end table
198    
199    In addition, the value @code{-0.0} is distinguishable from ordinary    To test whether a floating point value is a NaN, compare it with
200  zero in @acronym{IEEE} floating point (although @code{equal} and  itself using @code{=}.  That returns @code{nil} for a NaN, and
201  @code{=} consider them equal values).  @code{t} for any other floating point value.
202    
203      The value @code{-0.0} is distinguishable from ordinary zero in
204    @acronym{IEEE} floating point, but Emacs Lisp @code{equal} and
205    @code{=} consider them equal values.
206    
207    You can use @code{logb} to extract the binary exponent of a floating    You can use @code{logb} to extract the binary exponent of a floating
208  point number (or estimate the logarithm of an integer):  point number (or estimate the logarithm of an integer):

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