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

9 files changed, 77 insertions, 148 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
 
diff --git a/etc/ChangeLog b/etc/ChangeLog
index bba73855d6e..0eb21406105 100644
--- a/etc/ChangeLog
+++ b/etc/ChangeLog
@@ -1,8 +1,3 @@
-2011-05-03  Paul Eggert  <eggert@cs.ucla.edu>
-
-        * NEWS: Integer overflow now yields floating-point instead of
-        wrapping around.  (Bug#8611)
-
 2011-05-03  Leo Liu  <sdl.web@gmail.com>
 
         * NEWS: Mention the new command isearch-yank-pop.
diff --git a/etc/NEWS b/etc/NEWS
index 669c143ba7f..5094ecfc4fc 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -728,12 +728,6 @@ soap-inspect.el is an interactive inspector for SOAP WSDL structures.
 
 * Incompatible Lisp Changes in Emacs 24.1
 
-+++
-** Integer arithmetic overflow now yields the nearest floating-piont
-value rather than wrapping around.  For example, on a 32-bit machine,
-(1+ 536870911) yields 536870912.0, instead of the -536870912 it
-yielded in Emacs 23.3, or the 0 it yielded in Emacs 23.1.
-
 ---
 ** `char-direction-table' and the associated function `char-direction'
 were deleted.  They were buggy and inferior to the new support of
diff --git a/src/ChangeLog b/src/ChangeLog
index ee2db310562..2b4f498a0b9 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -11,16 +11,6 @@
 
         * term.c: Don't include <stdarg.h>, as <lisp.h> does that.
 
-        Arithmetic overflows now return float rather than wrapping around.
-        (Bug#8611).
-        * data.c: Include <intprops.h>.
-        (arith_driver): Use floating point if the accumulator would otherwise
-        go out of EMACS_INT range.
-        (arith_driver, Fadd1, Fsub1): Use floating point if the result is
-        out of Emacs fixnum range.
-        * bytecode.c (exec_byte_code): Likewise, for Bsub1, Badd1, Bnegate.
-        * floatfns.c (Fexpt): Likewise.
-
         * callproc.c (Fcall_process): Use 'volatile' to avoid vfork clobbering.
 
         * process.c (Fformat_network_address): Fix typo: args2 -> *args2.
diff --git a/src/bytecode.c b/src/bytecode.c
index ce79b011bbb..c3cd3d43072 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -1186,7 +1186,7 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           {
             Lisp_Object v1;
             v1 = TOP;
-            if (INTEGERP (v1) && MOST_NEGATIVE_FIXNUM < XINT (v1))
+            if (INTEGERP (v1))
               {
                 XSETINT (v1, XINT (v1) - 1);
                 TOP = v1;
@@ -1204,7 +1204,7 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           {
             Lisp_Object v1;
             v1 = TOP;
-            if (INTEGERP (v1) && XINT (v1) < MOST_POSITIVE_FIXNUM)
+            if (INTEGERP (v1))
               {
                 XSETINT (v1, XINT (v1) + 1);
                 TOP = v1;
@@ -1290,7 +1290,7 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           {
             Lisp_Object v1;
             v1 = TOP;
-            if (INTEGERP (v1) && - MOST_POSITIVE_FIXNUM <= XINT (v1))
+            if (INTEGERP (v1))
               {
                 XSETINT (v1, - XINT (v1));
                 TOP = v1;
diff --git a/src/data.c b/src/data.c
index beff570d552..577ae777d89 100644
--- a/src/data.c
+++ b/src/data.c
@@ -22,9 +22,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <signal.h>
 #include <stdio.h>
 #include <setjmp.h>
-
-#include <intprops.h>
-
 #include "lisp.h"
 #include "puresize.h"
 #include "character.h"
@@ -2429,8 +2426,10 @@ static Lisp_Object float_arith_driver (double, size_t, enum arithop,
 static Lisp_Object
 arith_driver (enum arithop code, size_t nargs, register Lisp_Object *args)
 {
+  register Lisp_Object val;
   register size_t argnum;
   register EMACS_INT accum = 0;
+  register EMACS_INT next;
 
   switch (SWITCH_ENUM_CAST (code))
     {
@@ -2452,89 +2451,58 @@ arith_driver (enum arithop code, size_t nargs, register Lisp_Object *args)
 
   for (argnum = 0; argnum < nargs; argnum++)
     {
-      EMACS_INT a = accum;
-      int use_float = 0;
-
       /* Using args[argnum] as argument to CHECK_NUMBER_... */
-      Lisp_Object val = args[argnum];
+      val = args[argnum];
       CHECK_NUMBER_OR_FLOAT_COERCE_MARKER (val);
-      args[argnum] = val;
 
       if (FLOATP (val))
-        use_float = 1;
-      else
+        return float_arith_driver ((double) accum, argnum, code,
+                                   nargs, args);
+      args[argnum] = val;
+      next = XINT (args[argnum]);
+      switch (SWITCH_ENUM_CAST (code))
         {
-          EMACS_INT next = XINT (val);
-          switch (SWITCH_ENUM_CAST (code))
+        case Aadd:
+          accum += next;
+          break;
+        case Asub:
+          accum = argnum ? accum - next : nargs == 1 ? - next : next;
+          break;
+        case Amult:
+          accum *= next;
+          break;
+        case Adiv:
+          if (!argnum)
+            accum = next;
+          else
             {
-            case Aadd:
-              if (next < 0
-                  ? a < TYPE_MINIMUM (EMACS_INT) - next
-                  : TYPE_MAXIMUM (EMACS_INT) - next < a)
-                use_float = 1;
-              else
-                a += next;
-              break;
-            case Asub:
-              if (argnum == 0 && nargs != 1)
-                a = next;
-              else if (next < 0
-                       ? TYPE_MAXIMUM (EMACS_INT) + next < a
-                       : a < TYPE_MINIMUM (EMACS_INT) + next)
-                use_float = 1;
-              else
-                a -= next;
-              break;
-            case Amult:
-              if (next < 0
-                  ? (a < 0
-                     ? a < TYPE_MAXIMUM (EMACS_INT) / next
-                     : next != -1 && TYPE_MINIMUM (EMACS_INT) / next < a)
-                  : (next != 0
-                     && (a < 0
-                         ? a < TYPE_MINIMUM (EMACS_INT) / next
-                         : TYPE_MAXIMUM (EMACS_INT) / next < a)))
-                use_float = 1;
-              else
-                a *= next;
-              break;
-            case Adiv:
-              if (!argnum)
-                a = next;
-              else
-                {
-                  if (next == 0)
-                    xsignal0 (Qarith_error);
-                  a /= next;
-                }
-              break;
-            case Alogand:
-              a &= next;
-              break;
-            case Alogior:
-              a |= next;
-              break;
-            case Alogxor:
-              a ^= next;
-              break;
-            case Amax:
-              if (!argnum || a < next)
-                a = next;
-              break;
-            case Amin:
-              if (!argnum || next < a)
-                a = next;
-              break;
+              if (next == 0)
+                xsignal0 (Qarith_error);
+              accum /= next;
             }
+          break;
+        case Alogand:
+          accum &= next;
+          break;
+        case Alogior:
+          accum |= next;
+          break;
+        case Alogxor:
+          accum ^= next;
+          break;
+        case Amax:
+          if (!argnum || next > accum)
+            accum = next;
+          break;
+        case Amin:
+          if (!argnum || next < accum)
+            accum = next;
+          break;
         }
-
-      if (use_float)
-        return float_arith_driver (accum, argnum, code, nargs, args);
-
-      accum = a;
     }
 
-  return make_fixnum_or_float (accum);
+  XSETINT (val, accum);
+  return val;
 }
 
 #undef isnan
@@ -2809,8 +2777,7 @@ Markers are converted to integers.  */)
 
   if (FLOATP (number))
     return (make_float (1.0 + XFLOAT_DATA (number)));
-  if (XINT (number) + 1 == MOST_POSITIVE_FIXNUM + 1)
-    return make_float (XINT (number) + 1);
+
   XSETINT (number, XINT (number) + 1);
   return number;
 }
@@ -2824,8 +2791,7 @@ Markers are converted to integers.  */)
 
   if (FLOATP (number))
     return (make_float (-1.0 + XFLOAT_DATA (number)));
-  if (XINT (number) - 1 == MOST_NEGATIVE_FIXNUM - 1)
-    return make_float (XINT (number) - 1);
+
   XSETINT (number, XINT (number) - 1);
   return number;
 }
diff --git a/src/floatfns.c b/src/floatfns.c
index 5c286772864..1232fc0afa1 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -491,39 +491,27 @@ DEFUN ("expt", Fexpt, Sexpt, 2, 2, 0,
       y = XINT (arg2);
       acc = 1;
 
-      if ((x == 0 && y != 0) || x == 1 || (x == -1 && (y & 1)))
-        return arg1;
-      if (x == -1)
-        y = 0;
-
-      while (1)
+      if (y < 0)
         {
-          if (y & 1)
-            {
-              if (x < 0
-                  ? (acc < 0
-                     ? acc < MOST_POSITIVE_FIXNUM / x
-                     : MOST_NEGATIVE_FIXNUM / x < acc)
-                  : (acc < 0
-                     ? acc < MOST_NEGATIVE_FIXNUM / x
-                     : MOST_POSITIVE_FIXNUM / x < acc))
-                break;
-              acc *= x;
-            }
-
-          y >>= 1;
-          if (y == 0)
+          if (x == 1)
+            acc = 1;
+          else if (x == -1)
+            acc = (y & 1) ? -1 : 1;
+          else
+            acc = 0;
+        }
+      else
+        {
+          while (y > 0)
             {
-              XSETINT (val, acc);
-              return val;
+              if (y & 1)
+                acc *= x;
+              x *= x;
+              y = (unsigned)y >> 1;
             }
-
-          if (x < 0
-              ? x < MOST_POSITIVE_FIXNUM / x
-              : MOST_POSITIVE_FIXNUM / x < x)
-            break;
-          x *= x;
         }
+      XSETINT (val, acc);
+      return val;
     }
   f1 = FLOATP (arg1) ? XFLOAT_DATA (arg1) : XINT (arg1);
   f2 = FLOATP (arg2) ? XFLOAT_DATA (arg2) : XINT (arg2);