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-rw-r--r--lib/builtins/ctzsi2.c96
1 files changed, 46 insertions, 50 deletions
diff --git a/lib/builtins/ctzsi2.c b/lib/builtins/ctzsi2.c
index c69486ea4..09c6863b7 100644
--- a/lib/builtins/ctzsi2.c
+++ b/lib/builtins/ctzsi2.c
@@ -1,57 +1,53 @@
-/* ===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------===
- *
- * 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 __ctzsi2 for the compiler_rt library.
- *
- * ===----------------------------------------------------------------------===
- */
+//===-- 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 */
+// Returns: the number of trailing 0-bits
-/* Precondition: a != 0 */
+// Precondition: a != 0
-COMPILER_RT_ABI 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) */
+COMPILER_RT_ABI 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));
+ // 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));
}