Initial import of compiler-rt.
-
git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@74292 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/ctzsi2.c b/lib/ctzsi2.c
new file mode 100644
index 0000000..1e6c2fe
--- /dev/null
+++ b/lib/ctzsi2.c
@@ -0,0 +1,54 @@
+//===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements __ctzsi2 for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "int_lib.h"
+
+// Returns: the number of trailing 0-bits
+
+// Precondition: a != 0
+
+si_int
+__ctzsi2(si_int a)
+{
+ su_int x = (su_int)a;
+ si_int t = ((x & 0x0000FFFF) == 0) << 4; // if (x has no small bits) t = 16 else 0
+ x >>= t; // x = [0 - 0xFFFF] + higher garbage bits
+ su_int r = t; // r = [0, 16]
+ // return r + ctz(x)
+ t = ((x & 0x00FF) == 0) << 3;
+ x >>= t; // x = [0 - 0xFF] + higher garbage bits
+ r += t; // r = [0, 8, 16, 24]
+ // return r + ctz(x)
+ t = ((x & 0x0F) == 0) << 2;
+ x >>= t; // x = [0 - 0xF] + higher garbage bits
+ r += t; // r = [0, 4, 8, 12, 16, 20, 24, 28]
+ // return r + ctz(x)
+ t = ((x & 0x3) == 0) << 1;
+ x >>= t;
+ x &= 3; // x = [0 - 3]
+ r += t; // r = [0 - 30] and is even
+ // return r + ctz(x)
+// The branch-less return statement below is equivalent
+// to the following switch statement:
+// switch (x)
+// {
+// case 0:
+// return r + 2;
+// case 2:
+// return r + 1;
+// case 1:
+// case 3:
+// return r;
+// }
+ return r + ((2 - (x >> 1)) & -((x & 1) == 0));
+}