3 files changed, 91 insertions, 49 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index ccf1fea9514..435f90abad9 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,13 @@
 2011-05-03  Paul Eggert  <eggert@cs.ucla.edu>
 
+        Arithmetic overflows now return float rather than wrapping around.
+        * 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.
+
         * 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 c3cd3d43072..ce79b011bbb 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))
+            if (INTEGERP (v1) && MOST_NEGATIVE_FIXNUM < XINT (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))
+            if (INTEGERP (v1) && XINT (v1) < MOST_POSITIVE_FIXNUM)
               {
                 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))
+            if (INTEGERP (v1) && - MOST_POSITIVE_FIXNUM <= XINT (v1))
               {
                 XSETINT (v1, - XINT (v1));
                 TOP = v1;
diff --git a/src/data.c b/src/data.c
index 577ae777d89..beff570d552 100644
--- a/src/data.c
+++ b/src/data.c
@@ -22,6 +22,9 @@ 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"
@@ -2426,10 +2429,8 @@ 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))
     {
@@ -2451,58 +2452,89 @@ 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_... */
-      val = args[argnum];
+      Lisp_Object val = args[argnum];
       CHECK_NUMBER_OR_FLOAT_COERCE_MARKER (val);
+      args[argnum] = val;
 
       if (FLOATP (val))
-        return float_arith_driver ((double) accum, argnum, code,
-                                   nargs, args);
-      args[argnum] = val;
-      next = XINT (args[argnum]);
-      switch (SWITCH_ENUM_CAST (code))
+        use_float = 1;
+      else
         {
-        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
+          EMACS_INT next = XINT (val);
+          switch (SWITCH_ENUM_CAST (code))
             {
-              if (next == 0)
-                xsignal0 (Qarith_error);
-              accum /= next;
+            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;
             }
-          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;
     }
 
-  XSETINT (val, accum);
-  return val;
+  return make_fixnum_or_float (accum);
 }
 
 #undef isnan
@@ -2777,7 +2809,8 @@ 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;
 }
@@ -2791,7 +2824,8 @@ 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;
 }