* floatfns.c (Fexpt): Likewise.

2 files changed, 30 insertions, 17 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 435f90abad9..26b3af3225c 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -7,6 +7,7 @@
         (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.
 
diff --git a/src/floatfns.c b/src/floatfns.c
index 1232fc0afa1..5c286772864 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -491,27 +491,39 @@ DEFUN ("expt", Fexpt, Sexpt, 2, 2, 0,
       y = XINT (arg2);
       acc = 1;
 
-      if (y < 0)
-        {
-          if (x == 1)
-            acc = 1;
-          else if (x == -1)
-            acc = (y & 1) ? -1 : 1;
-          else
-            acc = 0;
-        }
-      else
+      if ((x == 0 && y != 0) || x == 1 || (x == -1 && (y & 1)))
+        return arg1;
+      if (x == -1)
+        y = 0;
+
+      while (1)
         {
-          while (y > 0)
+          if (y & 1)
             {
-              if (y & 1)
-                acc *= x;
-              x *= x;
-              y = (unsigned)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)
+            {
+              XSETINT (val, acc);
+              return val;
+            }
+
+          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);