1 files changed, 53 insertions, 0 deletions
diff --git a/cpukit/compiler-rt/lib/builtins/ctzsi2.c b/cpukit/compiler-rt/lib/builtins/ctzsi2.c
new file mode 100644
index 0000000000..ed95c60579
--- /dev/null
+++ b/cpukit/compiler-rt/lib/builtins/ctzsi2.c
@@ -0,0 +1,53 @@
+//===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements __ctzsi2 for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "int_lib.h"
+
+// Returns: the number of trailing 0-bits
+
+// Precondition: a != 0
+
+COMPILER_RT_ABI 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));
+}