1 files changed, 48 insertions, 0 deletions
diff --git a/cpukit/compiler-rt/lib/builtins/clzsi2.c b/cpukit/compiler-rt/lib/builtins/clzsi2.c
new file mode 100644
index 0000000000..d75f56d937
--- /dev/null
+++ b/cpukit/compiler-rt/lib/builtins/clzsi2.c
@@ -0,0 +1,48 @@
+//===-- clzsi2.c - Implement __clzsi2 -------------------------------------===//
+//
+// 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 __clzsi2 for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "int_lib.h"
+
+// Returns: the number of leading 0-bits
+
+// Precondition: a != 0
+
+COMPILER_RT_ABI int __clzsi2(si_int a) {
+  su_int x = (su_int)a;
+  si_int t = ((x & 0xFFFF0000) == 0) << 4; // if (x is small) t = 16 else 0
+  x >>= 16 - t;                            // x = [0 - 0xFFFF]
+  su_int r = t;                            // r = [0, 16]
+  // return r + clz(x)
+  t = ((x & 0xFF00) == 0) << 3;
+  x >>= 8 - t; // x = [0 - 0xFF]
+  r += t;      // r = [0, 8, 16, 24]
+  // return r + clz(x)
+  t = ((x & 0xF0) == 0) << 2;
+  x >>= 4 - t; // x = [0 - 0xF]
+  r += t;      // r = [0, 4, 8, 12, 16, 20, 24, 28]
+  // return r + clz(x)
+  t = ((x & 0xC) == 0) << 1;
+  x >>= 2 - t; // x = [0 - 3]
+  r += t;      // r = [0 - 30] and is even
+  // return r + clz(x)
+  //     switch (x)
+  //     {
+  //     case 0:
+  //         return r + 2;
+  //     case 1:
+  //         return r + 1;
+  //     case 2:
+  //     case 3:
+  //         return r;
+  //     }
+  return r + ((2 - x) & -((x & 2) == 0));
+}