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* numbers.texi: Improve and clarify a bit, and fix some minor bugs.

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Remove now-obsolete hypothetical note about negative division,
as the C standard has changed.
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Paul Eggert 2014-03-19 14:21:01 -07:00
parent d16ae62288
commit c7dff2f665
2 changed files with 23 additions and 23 deletions
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4
doc/lispref/ChangeLog
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@ -1,5 +1,9 @@
2014-03-19 Paul Eggert <eggert@cs.ucla.edu>
* numbers.texi: Improve and clarify a bit, and fix some minor bugs.
Remove now-obsolete hypothetical note about negative division,
as the C standard has changed.
Fix porting inconsistency about rounding to even.
* numbers.texi (Numeric Conversions, Rounding Operations):
Document that 'round' and 'fround' round to even.

42
doc/lispref/numbers.texi
View file

@ -116,8 +116,8 @@ use the @samp{...} notation to make binary integers easier to read.)
@minus{}1 is represented as 30 ones. (This is called @dfn{two's
complement} notation.)
The negative integer, @minus{}5, is creating by subtracting 4 from
@minus{}1. In binary, the decimal integer 4 is 100. Consequently,
Subtracting 4 from @minus{}1 returns the negative integer @minus{}5.
In binary, the decimal integer 4 is 100. Consequently,
@minus{}5 looks like this:
@example
@ -190,8 +190,8 @@ on 64-bit platforms.
@end defvar
In Emacs Lisp, text characters are represented by integers. Any
integer between zero and the value of @code{max-char}, inclusive, is
considered to be valid as a character. @xref{String Basics}.
integer between zero and the value of @code{(max-char)}, inclusive, is
considered to be valid as a character. @xref{Character Codes}.
@node Float Basics
@section Floating-Point Basics
@ -252,7 +252,7 @@ This function returns a cons cell @code{(@var{s} . @var{e})},
where @var{s} and @var{e} are respectively the significand and
exponent of the floating-point number @var{x}.
If @var{x} is finite, @var{s} is a floating-point number between 0.5
If @var{x} is finite, then @var{s} is a floating-point number between 0.5
(inclusive) and 1.0 (exclusive), @var{e} is an integer, and
@ifnottex
@var{x} = @var{s} * 2**@var{e}.
@ -260,9 +260,9 @@ If @var{x} is finite, @var{s} is a floating-point number between 0.5
@tex
@math{x = s 2^e}.
@end tex
If @var{x} is zero or infinity, @var{s} is the same as @var{x}.
If @var{x} is a NaN, @var{s} is also a NaN.
If @var{x} is zero, @var{e} is 0.
If @var{x} is zero or infinity, then @var{s} is the same as @var{x}.
If @var{x} is a NaN, then @var{s} is also a NaN.
If @var{x} is zero, then @var{e} is 0.
@end defun
@defun ldexp sig &optional exp
@ -275,9 +275,9 @@ This function copies the sign of @var{x2} to the value of @var{x1},
and returns the result. @var{x1} and @var{x2} must be floating point.
@end defun
@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
@defun logb x
This function returns the binary exponent of @var{x}. More
precisely, the value is the logarithm base 2 of @math{|x|}, rounded
down to an integer.
@example
@ -367,7 +367,7 @@ Here's a function to do this:
@example
(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(or (and (= x 0) (= y 0))
(or (= x y)
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor)))
@ -648,10 +648,6 @@ number or a marker.
If all the arguments are integers, the result is an integer, obtained
by rounding the quotient towards zero after each division.
(Hypothetically, some machines may have different rounding behavior
for negative arguments, because @code{/} is implemented using the C
division operator, which permits machine-dependent rounding; but this
does not happen in practice.)
@example
@group
@ -706,8 +702,7 @@ For any two integers @var{dividend} and @var{divisor},
@end example
@noindent
always equals @var{dividend}. If @var{divisor} is zero, Emacs signals
an @code{arith-error} error.
always equals @var{dividend} if @var{divisor} is nonzero.
@example
(% 9 4)
@ -769,7 +764,8 @@ For any two numbers @var{dividend} and @var{divisor},
@noindent
always equals @var{dividend}, subject to rounding error if either
argument is floating point. For @code{floor}, see @ref{Numeric
argument is floating point and to an @code{arith-error} if @var{dividend} is an
integer and @var{divisor} is 0. For @code{floor}, see @ref{Numeric
Conversions}.
@end defun
@ -1194,8 +1190,8 @@ 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,
@code{sqrt} returns a NaN.
This returns the square root of @var{arg}. If @var{arg} is finite
and less than zero, @code{sqrt} returns a NaN.
@end defun
In addition, Emacs defines the following common mathematical
@ -1244,8 +1240,8 @@ any integer representable in Lisp, i.e., an integer between
@code{most-negative-fixnum} and @code{most-positive-fixnum}
(@pxref{Integer Basics}).
If @var{limit} is @code{t}, it means to choose a new seed based on the
current time of day and on Emacs's process @acronym{ID} number.
If @var{limit} is @code{t}, it means to choose a new seed as if Emacs
were restarting.
If @var{limit} is a string, it means to choose a new seed based on the
string's contents.