Optimize `1+' and `1-' on fixnums.

* libguile/vm-i-scheme.c (INUM_MAX, INUM_MIN): New macros.
  (add1, sub1): Add/subtract without untagging the operand.  This leads
  to a 44% run time improvement compared to the previous
  implementation.

* libguile/vm.c: Include <stdint.h>.

* test-suite/tests/numbers.test ("1+", "1-"): Add tests for
  MOST-POSITIVE-FIXNUM, resp. MOST-NEGATIVE-FIXNUM, for 32-bit and
  34-bit values thereof.

* benchmark-suite/benchmarks/arithmetic.bm: New file.

* benchmark-suite/Makefile.am (SCM_BENCHMARKS): Add it.

5 files changed, 92 insertions, 10 deletions

diff --git a/benchmark-suite/Makefile.am b/benchmark-suite/Makefile.am
index e2aad9148..63f490cd4 100644
--- a/benchmark-suite/Makefile.am
+++ b/benchmark-suite/Makefile.am
@@ -1,4 +1,5 @@
 SCM_BENCHMARKS = benchmarks/0-reference.bm		\
+		 benchmarks/arithmetic.bm		\
 		 benchmarks/bytevectors.bm		\
 		 benchmarks/chars.bm			\
 		 benchmarks/continuations.bm		\
diff --git a/benchmark-suite/benchmarks/arithmetic.bm b/benchmark-suite/benchmarks/arithmetic.bm
new file mode 100644
index 000000000..cd8bbbd7b
--- /dev/null
+++ b/benchmark-suite/benchmarks/arithmetic.bm
@@ -0,0 +1,46 @@
+;;; -*- mode: scheme; coding: utf-8; -*-
+;;; Integer arithmetic.
+;;;
+;;; Copyright 2010 Free Software Foundation, Inc.
+;;;
+;;; This program is free software; you can redistribute it and/or
+;;; modify it under the terms of the GNU Lesser General Public License
+;;; as published by the Free Software Foundation; either version 3, or
+;;; (at your option) any later version.
+;;;
+;;; This program is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public
+;;; License along with this software; see the file COPYING.LESSER.  If
+;;; not, write to the Free Software Foundation, Inc., 51 Franklin
+;;; Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+(define-module (benchmarks arithmetic)
+  #:use-module (benchmark-suite lib))
+
+(define-syntax repeat
+  (lambda (s)
+    ;; Construct an expression of the form `(OP (OP (OP BODY)))', with a
+    ;; depth of COUNT.
+    (syntax-case s ()
+      ((_ op body count)
+       (number? (syntax->datum #'count))
+       (let loop ((count  (syntax->datum #'count))
+                  (result #'body))
+         (if (= 0 count)
+             result
+             (loop (1- count)
+                   (with-syntax ((result result))
+                     #'(op result)))))))))
+
+
+(with-benchmark-prefix "fixnum"
+
+  (benchmark "1+" 1e7
+    (repeat 1+ 2 100))
+
+  (benchmark "1-" 1e7
+    (repeat 1- 2 100)))
diff --git a/libguile/vm-i-scheme.c b/libguile/vm-i-scheme.c
index 69ea8a544..3e80a0ef5 100644
--- a/libguile/vm-i-scheme.c
+++ b/libguile/vm-i-scheme.c
@@ -209,6 +209,10 @@ VM_DEFINE_FUNCTION (149, ge, "ge?", 2)
  * Numeric functions
  */
 
+/* The maximum/minimum tagged integers.  */
+#define INUM_MAX (INTPTR_MAX - 1)
+#define INUM_MIN (INTPTR_MIN + scm_tc2_int)
+
 #undef FUNC2
 #define FUNC2(CFUNC,SFUNC)				\
 {							\
@@ -231,12 +235,21 @@ VM_DEFINE_FUNCTION (150, add, "add", 2)
 VM_DEFINE_FUNCTION (151, add1, "add1", 1)
 {
   ARGS1 (x);
-  if (SCM_I_INUMP (x))
+
+  /* Check for overflow.  */
+  if (SCM_LIKELY ((scm_t_intptr) x < INUM_MAX))
     {
-      scm_t_int64 n = SCM_I_INUM (x) + 1;
-      if (SCM_FIXABLE (n))
-	RETURN (SCM_I_MAKINUM (n));
+      SCM result;
+
+      /* Add the integers without untagging.  */
+      result = SCM_PACK ((scm_t_intptr) x
+			 + (scm_t_intptr) SCM_I_MAKINUM (1)
+			 - scm_tc2_int);
+
+      if (SCM_LIKELY (SCM_I_INUMP (result)))
+	RETURN (result);
     }
+
   SYNC_REGISTER ();
   RETURN (scm_sum (x, SCM_I_MAKINUM (1)));
 }
@@ -249,12 +262,21 @@ VM_DEFINE_FUNCTION (152, sub, "sub", 2)
 VM_DEFINE_FUNCTION (153, sub1, "sub1", 1)
 {
   ARGS1 (x);
-  if (SCM_I_INUMP (x))
+
+  /* Check for underflow.  */
+  if (SCM_LIKELY ((scm_t_intptr) x > INUM_MIN))
     {
-      scm_t_int64 n = SCM_I_INUM (x) - 1;
-      if (SCM_FIXABLE (n))
-	RETURN (SCM_I_MAKINUM (n));
+      SCM result;
+
+      /* Substract the integers without untagging.  */
+      result = SCM_PACK ((scm_t_intptr) x
+			 - (scm_t_intptr) SCM_I_MAKINUM (1)
+			 + scm_tc2_int);
+
+      if (SCM_LIKELY (SCM_I_INUMP (result)))
+	RETURN (result);
     }
+
   SYNC_REGISTER ();
   RETURN (scm_difference (x, SCM_I_MAKINUM (1)));
 }
diff --git a/libguile/vm.c b/libguile/vm.c
index 58d9a9f80..e1a90e127 100644
--- a/libguile/vm.c
+++ b/libguile/vm.c
@@ -24,6 +24,7 @@
 #include <alloca.h>
 #include <alignof.h>
 #include <string.h>
+#include <stdint.h>
 
 #include "libguile/bdw-gc.h"
 #include <gc/gc_mark.h>
diff --git a/test-suite/tests/numbers.test b/test-suite/tests/numbers.test
index 1d7cb7c21..3c3e14fed 100644
--- a/test-suite/tests/numbers.test
+++ b/test-suite/tests/numbers.test
@@ -109,7 +109,13 @@
   (pass-if (eqv? 1 (1+ 0)))
   (pass-if (eqv? 0 (1+ -1)))
   (pass-if (eqv? 101 (1+ 100)))
-  (pass-if (eqv? -99 (1+ -100))))
+  (pass-if (eqv? -99 (1+ -100)))
+
+  ;; The maximum fixnum on a 32-bit architecture: 2^29 - 1.
+  (pass-if (eqv? 536870912 (1+ 536870911)))
+
+  ;; The maximum fixnum on a 64-bit architecture: 2^61 - 1.
+  (pass-if (eqv? 2305843009213693952 (1+ 2305843009213693951))))
 
 ;;;
 ;;; 1-
@@ -123,7 +129,13 @@
   (pass-if (eqv? -1 (1- 0)))
   (pass-if (eqv? 0 (1- 1)))
   (pass-if (eqv? 99 (1- 100)))
-  (pass-if (eqv? -101 (1- -100))))
+  (pass-if (eqv? -101 (1- -100)))
+
+  ;; The minimum fixnum on a 32-bit architecture: -2^29.
+  (pass-if (eqv? -536870913 (1- -536870912)))
+
+  ;; The minimum fixnum on a 64-bit architecture: -2^61.
+  (pass-if (eqv? -2305843009213693953 (1- -2305843009213693952))))
 
 ;;;
 ;;; ash