1/*
2 * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25#ifndef SHARE_UTILITIES_COUNT_TRAILING_ZEROS_HPP
26#define SHARE_UTILITIES_COUNT_TRAILING_ZEROS_HPP
27
28#include "utilities/debug.hpp"
29#include "utilities/globalDefinitions.hpp"
30
31// unsigned count_trailing_zeros(uintx x)
32// Return the number of trailing zeros in x, e.g. the zero-based index
33// of the least significant set bit in x.
34// Precondition: x != 0.
35
36// Dispatch on toolchain to select implementation.
37
38/*****************************************************************************
39 * GCC and compatible (including Clang)
40 *****************************************************************************/
41#if defined(TARGET_COMPILER_gcc)
42
43inline unsigned count_trailing_zeros(uintx x) {
44 STATIC_ASSERT(sizeof(unsigned long) == sizeof(uintx));
45 assert(x != 0, "precondition");
46 return __builtin_ctzl(x);
47}
48
49/*****************************************************************************
50 * Microsoft Visual Studio
51 *****************************************************************************/
52#elif defined(TARGET_COMPILER_visCPP)
53
54#include <intrin.h>
55
56#ifdef _LP64
57#pragma intrinsic(_BitScanForward64)
58#else
59#pragma intrinsic(_BitScanForward)
60#endif
61
62inline unsigned count_trailing_zeros(uintx x) {
63 assert(x != 0, "precondition");
64 unsigned long index;
65#ifdef _LP64
66 _BitScanForward64(&index, x);
67#else
68 _BitScanForward(&index, x);
69#endif
70 return index;
71}
72
73/*****************************************************************************
74 * IBM XL C/C++
75 *****************************************************************************/
76#elif defined(TARGET_COMPILER_xlc)
77
78#include <builtins.h>
79
80inline unsigned count_trailing_zeros(uintx x) {
81 assert(x != 0, "precondition");
82#ifdef _LP64
83 return __cnttz8(x);
84#else
85 return __cnttz4(x);
86#endif
87}
88
89/*****************************************************************************
90 * Oracle Studio
91 *****************************************************************************/
92#elif defined(TARGET_COMPILER_solstudio)
93
94// No compiler built-in / intrinsic, so use inline assembler.
95
96#include "utilities/macros.hpp"
97
98#include OS_CPU_HEADER(count_trailing_zeros)
99
100/*****************************************************************************
101 * Unknown toolchain
102 *****************************************************************************/
103#else
104#error Unknown TARGET_COMPILER
105
106#endif // Toolchain dispatch
107
108#endif // SHARE_UTILITIES_COUNT_TRAILING_ZEROS_HPP
109