Revert to wraparound integer arithmetic, instead of going to float.

3 files changed, 11 insertions, 15 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index bca76b8a23c..163de31f220 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,9 +1,6 @@
 2011-05-03  Paul Eggert  <eggert@cs.ucla.edu>
 
         * numbers.texi (Integer Basics): Large integers are treated as floats.
-        (Arithmetic Operations, Math Functions): Large integers go to
-        floats instead of wrapping around.
-        * objects.texi (Integer Type): Likewise.  (Bug#8611)
 
 2011-04-30  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
diff --git a/doc/lispref/numbers.texi b/doc/lispref/numbers.texi
index ebf5660febe..2c73a03a26c 100644
--- a/doc/lispref/numbers.texi
+++ b/doc/lispref/numbers.texi
@@ -507,9 +507,9 @@ commonly used.
   All of these functions except @code{%} return a floating point value
 if any argument is floating.
 
-  If integer arithmetic overflows, the resulting value is converted
-to floating point.  Thus @code{(1+ 536870911)} may evaluate to
-536870912.0, depending on your hardware.
+  It is important to note that in Emacs Lisp, arithmetic functions
+do not check for overflow.  Thus @code{(1+ 268435455)} may evaluate to
+@minus{}268435456, depending on your hardware.
 
 @defun 1+ number-or-marker
 This function returns @var{number-or-marker} plus 1.
@@ -826,7 +826,7 @@ On the other hand, shifting one place to the right looks like this:
 As the example illustrates, shifting one place to the right divides the
 value of a positive integer by two, rounding downward.
 
-The function @code{lsh} does
+The function @code{lsh}, like all Emacs Lisp arithmetic functions, does
 not check for overflow, so shifting left can discard significant bits
 and change the sign of the number.  For example, left shifting
 536,870,911 produces @minus{}2 on a 30-bit machine:
@@ -1169,8 +1169,8 @@ approximately.
 
 @defun expt x y
 This function returns @var{x} raised to power @var{y}.  If both
-arguments are integers and @var{y} is nonnegative, the result is an
-integer if it is in Emacs integer range.
+arguments are integers and @var{y} is positive, the result is an
+integer; in this case, overflow causes truncation, so watch out.
 @end defun
 
 @defun sqrt arg
diff --git a/doc/lispref/objects.texi b/doc/lispref/objects.texi
index 6dd7878e53b..c58d54f13fc 100644
--- a/doc/lispref/objects.texi
+++ b/doc/lispref/objects.texi
@@ -179,10 +179,10 @@ to
 @tex
 @math{2^{29}-1})
 @end tex
-on most machines.  (Some machines may provide a wider range.)
-If integer arithmetic overflows, the resulting value is converted
-+to floating point.  Thus @code{(1+ 536870911)} may evaluate to
-+536870912.0, depending on your hardware.
+on most machines.  (Some machines may provide a wider range.)  It is
+important to note that the Emacs Lisp arithmetic functions do not check
+for overflow.  Thus @code{(1+ 536870911)} is @minus{}536870912 on most
+machines.
 
   The read syntax for integers is a sequence of (base ten) digits with an
 optional sign at the beginning and an optional period at the end.  The
@@ -195,8 +195,7 @@ leading @samp{+} or a final @samp{.}.
 1                ; @r{The integer 1.}
 1.               ; @r{Also the integer 1.}
 +1               ; @r{Also the integer 1.}
-1073741825       ; @r{The floating point number 1073741825.0,}
-                 ; @r{on a 30-bit implementation.}
+1073741825       ; @r{Also the integer 1 on a 30-bit implementation.}
 @end group
 @end example