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
diff --git a/lib/muloti4.c b/lib/muloti4.c
new file mode 100644
index 0000000..bf1ab04
--- /dev/null
+++ b/lib/muloti4.c
@@ -0,0 +1,63 @@
+/*===-- muloti4.c - Implement __muloti4 -----------------------------------===
+ *
+ * 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 __muloti4 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#if __x86_64
+
+#include "int_lib.h"
+#include <stdlib.h>
+
+/* Returns: a * b */
+
+/* Effects: sets *overflow to 1 if a * b overflows */
+
+ti_int
+__muloti4(ti_int a, ti_int b, int* overflow)
+{
+ const int N = (int)(sizeof(ti_int) * CHAR_BIT);
+ const ti_int MIN = (ti_int)1 << (N-1);
+ const ti_int MAX = ~MIN;
+ *overflow = 0;
+ ti_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;
+ }
+ ti_int sa = a >> (N - 1);
+ ti_int abs_a = (a ^ sa) - sa;
+ ti_int sb = b >> (N - 1);
+ ti_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;
+}
+
+#endif