From 1ace4055f79f304750839d73c46bbcaeb994f1b5 Mon Sep 17 00:00:00 2001
From: Eric Christopher <echristo@apple.com>
Date: Fri, 17 Jun 2011 20:17:05 +0000
Subject: Implement mulo<mode>4 for use in signed overflow checking.

Fixes rdar://9219742 and rdar://9218244


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@133284 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/mulodi4.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 lib/mulodi4.c

(limited to 'lib/mulodi4.c')

diff --git a/lib/mulodi4.c b/lib/mulodi4.c
new file mode 100644
index 000000000..dcaf6ab86
--- /dev/null
+++ b/lib/mulodi4.c
@@ -0,0 +1,59 @@
+/*===-- mulodi4.c - Implement __mulodi4 -----------------------------------===
+ *
+ *                     The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __mulodi4 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+#include <stdlib.h>
+
+/* Returns: a * b */
+
+/* Effects: sets *overflow to 1  if a * b overflows */
+
+di_int
+__mulodi4(di_int a, di_int b, int* overflow)
+{
+    const int N = (int)(sizeof(di_int) * CHAR_BIT);
+    const di_int MIN = (di_int)1 << (N-1);
+    const di_int MAX = ~MIN;
+    *overflow = 0; 
+    di_int result = a * b;
+    if (a == MIN)
+    {
+        if (b != 0 && b != 1)
+	    *overflow = 1;
+	return result;
+    }
+    if (b == MIN)
+    {
+        if (a != 0 && a != 1)
+	    *overflow = 1;
+        return result;
+    }
+    di_int sa = a >> (N - 1);
+    di_int abs_a = (a ^ sa) - sa;
+    di_int sb = b >> (N - 1);
+    di_int abs_b = (b ^ sb) - sb;
+    if (abs_a < 2 || abs_b < 2)
+        return result;
+    if (sa == sb)
+    {
+        if (abs_a > MAX / abs_b)
+            *overflow = 1;
+    }
+    else
+    {
+        if (abs_a > MIN / -abs_b)
+            *overflow = 1;
+    }
+    return result;
+}
-- 
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