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Diffstat (limited to 'doc/lispref/numbers.texi')
| -rw-r--r-- | doc/lispref/numbers.texi | 35 |
1 files changed, 22 insertions, 13 deletions
diff --git a/doc/lispref/numbers.texi b/doc/lispref/numbers.texi index 17f3ee099b..7c9672a38c 100644 --- a/doc/lispref/numbers.texi +++ b/doc/lispref/numbers.texi @@ -196,6 +196,14 @@ numerical functions return such values in cases where there is no correct answer. For example, @code{(/ 0.0 0.0)} returns a NaN. (NaN values can also carry a sign, but for practical purposes there's no significant difference between different NaN values in Emacs Lisp.) + +When a function is documented to return a NaN, it returns an +implementation-defined value when Emacs is running on one of the +now-rare platforms that do not use @acronym{IEEE} floating point. For +example, @code{(log -1.0)} typically returns a NaN, but on +non-@acronym{IEEE} platforms it returns an implementation-defined +value. + Here are the read syntaxes for these special floating point values: @table @asis @@ -241,7 +249,7 @@ numbers. @defun logb number This function returns the binary exponent of @var{number}. More -precisely, the value is the logarithm of @var{number} base 2, rounded +precisely, the value is the logarithm of |@var{number}| base 2, rounded down to an integer. @example @@ -694,7 +702,8 @@ arguments. It also permits floating point arguments; it rounds the quotient downward (towards minus infinity) to an integer, and uses that quotient to compute the remainder. -An @code{arith-error} results if @var{divisor} is 0. +If @var{divisor} is zero, @code{mod} signals an @code{arith-error} +error if both arguments are integers, and returns a NaN otherwise. @example @group @@ -1096,8 +1105,8 @@ pi/2 @tex @math{\pi/2} @end tex -(inclusive) whose sine is @var{arg}; if, however, @var{arg} is out of -range (outside [@minus{}1, 1]), it signals a @code{domain-error} error. +(inclusive) whose sine is @var{arg}. If @var{arg} is out of range +(outside [@minus{}1, 1]), @code{asin} returns a NaN. @end defun @defun acos arg @@ -1108,8 +1117,8 @@ pi @tex @math{\pi} @end tex -(inclusive) whose cosine is @var{arg}; if, however, @var{arg} is out -of range (outside [@minus{}1, 1]), it signals a @code{domain-error} error. +(inclusive) whose cosine is @var{arg}. If @var{arg} is out of range +(outside [@minus{}1, 1]), @code{acos} returns a NaN. @end defun @defun atan y &optional x @@ -1141,8 +1150,8 @@ This is the exponential function; it returns @math{e} to the power @defun log arg &optional base This function returns the logarithm of @var{arg}, with base @var{base}. If you don't specify @var{base}, the natural base -@math{e} is used. If @var{arg} is negative, it signals a -@code{domain-error} error. +@math{e} is used. If @var{arg} or @var{base} is negative, @code{log} +returns a NaN. @end defun @ignore @@ -1160,21 +1169,21 @@ lose accuracy. @end ignore @defun log10 arg -This function returns the logarithm of @var{arg}, with base 10. If -@var{arg} is negative, it signals a @code{domain-error} error. -@code{(log10 @var{x})} @equiv{} @code{(log @var{x} 10)}, at least -approximately. +This function returns the logarithm of @var{arg}, with base 10: +@code{(log10 @var{x})} @equiv{} @code{(log @var{x} 10)}. @end defun @defun expt x y This function returns @var{x} raised to power @var{y}. If both arguments are integers and @var{y} is positive, the result is an integer; in this case, overflow causes truncation, so watch out. +If @var{x} is a finite negative number and @var{y} is a finite +non-integer, @code{expt} returns a NaN. @end defun @defun sqrt arg This returns the square root of @var{arg}. If @var{arg} is negative, -it signals a @code{domain-error} error. +@code{sqrt} returns a NaN. @end defun In addition, Emacs defines the following common mathematical |