From 72a8824940eb6d26bd30ce91c6056bca8d4c1a16 Mon Sep 17 00:00:00 2001
From: Neil Brown <neil@twistedsquare.com>
Date: Thu, 22 Jan 2009 16:51:54 +0000
Subject: [PATCH] Had a go at implementing multiply overflow checking (with a
 single division, and pre-checks)

I also added an occam testcase to help time the different between * and TIMES.  But gcc optimises out the loop with TIMES under -O2, and with -O0 there is a factor of four difference.
---
 rangetest.c            |  2 +-
 support/tock_support.h | 23 ++++++++++++++++++++---
 testcases/time-mul.occ | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 4 deletions(-)
 create mode 100644 testcases/time-mul.occ

diff --git a/rangetest.c b/rangetest.c
index cdd4e5d..8c87f14 100644
--- a/rangetest.c
+++ b/rangetest.c
@@ -13,7 +13,7 @@ int g_stopped;
 		passes++; \
 	} else { \
 		failures++; \
-		report_failure(#call " failed, expected to stop\n"); \
+		report_failure(#call " failed, expected to stop, got: %lld\n", (int64_t)call); \
 	} \
   } while(0)
 
diff --git a/support/tock_support.h b/support/tock_support.h
index d9305ba..7603fb7 100644
--- a/support/tock_support.h
+++ b/support/tock_support.h
@@ -143,8 +143,25 @@ static inline int occam_check_retype (int src, int dest, const char *pos) {
 #define MAKE_MUL(type) \
 	static inline type occam_mul_##type (type, type, const char *) occam_unused; \
 	static inline type occam_mul_##type (type a, type b, const char *pos) { \
-		return a * b; /*TODO*/ \
+		if (( (a < 0 ? -a : a) >> ((sizeof(type)*CHAR_BIT/2)-1) \
+		   | (b < 0 ? -b : b) >> ((sizeof(type)*CHAR_BIT/2)-1)) == 0) { \
+            /*overflow not possible on such small numbers*/ \
+            return a * b; \
+        } else if (b == 0) { \
+        	return 0; \
+        } else { \
+        	const type r = a * b; \
+        	/* Taken from: http://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg326431.html */ \
+        	if (r / b != a) { \
+        		occam_stop(pos, 3, "integer overflow when doing %d * %d", a, b); \
+        	} else { \
+        		return r; \
+        	} \
+        } \
 	}
+#define MAKE_MULF(type) \
+	static inline type occam_mul_##type (type, type, const char *) occam_unused; \
+	static inline type occam_mul_##type (type a, type b, const char *pos) { return a * b;}
 #define MAKE_DIV(type) \
 	static inline type occam_div_##type (type, type, const char *) occam_unused; \
 	static inline type occam_div_##type (type a, type b, const char *pos) { \
@@ -295,7 +312,7 @@ MAKE_ALL_SIGNED(int64_t, "%lld", uint64_t)
 MAKE_RANGE_CHECK(float, "%f")
 MAKE_ADDF(float)
 MAKE_SUBTRF(float)
-MAKE_MUL(float)
+MAKE_MULF(float)
 MAKE_DIVF(float)
 MAKE_NEGATEF(float)
 MAKE_DUMB_REM(float)
@@ -304,7 +321,7 @@ MAKE_DUMB_REM(float)
 MAKE_RANGE_CHECK(double, "%f")
 MAKE_ADDF(double)
 MAKE_SUBTRF(double)
-MAKE_MUL(double)
+MAKE_MULF(double)
 MAKE_DIVF(double)
 MAKE_NEGATEF(double)
 MAKE_DUMB_REM(double)
diff --git a/testcases/time-mul.occ b/testcases/time-mul.occ
new file mode 100644
index 0000000..a730d02
--- /dev/null
+++ b/testcases/time-mul.occ
@@ -0,0 +1,38 @@
+#INCLUDE "course.occ"
+
+PROC main(CHAN OF BYTE out)
+  TIMER t:
+  INT t0, t1, x:
+  SEQ
+    t ? t0
+    SEQ i = 0 FOR 100000
+      x := i * 5
+    t ? t1
+    t1 := t1 - t0
+    out.string("Time for low numbers MUL: ", 0, out)
+    out.int(t1, 0, out)
+
+    t ? t0
+    SEQ i = 0 FOR 100000
+      x := i TIMES 5
+    t ? t1
+    t1 := t1 - t0
+    out.string("Time for low numbers TIMES: ", 0, out)
+    out.int(t1, 0, out)
+
+    t ? t0
+    SEQ i = 100000000 FOR 100000
+      x := i * 5
+    t ? t1
+    t1 := t1 - t0
+    out.string("Time for high numbers MUL: ", 0, out)
+    out.int(t1, 0, out)
+    
+    t ? t0
+    SEQ i = 100000000 FOR 100000
+      x := i TIMES 5
+    t ? t1
+    t1 := t1 - t0
+    out.string("Time for high numbers TIMES: ", 0, out)
+    out.int(t1, 0, out)
+: