1 /*
   2  * Copyright (c) 2017, 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_VM_UTILITIES_COUNTTRAILINGZEROS_HPP
  26 #define SHARE_VM_UTILITIES_COUNTTRAILINGZEROS_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 #if defined(TARGET_COMPILER_gcc)
  40 
  41 inline unsigned count_trailing_zeros(uintx x) {
  42   STATIC_ASSERT(sizeof(unsigned long) == sizeof(uintx));
  43   assert(x != 0, "precondition");
  44   return __builtin_ctzl(x);
  45 }
  46 
  47 //////////////////////////////////////////////////////////////////////////////
  48 #elif defined(TARGET_COMPILER_visCPP)
  49 
  50 #include <intrin.h>
  51 
  52 #ifdef _LP64
  53 #pragma intrinsic(_BitScanForward64)
  54 #else
  55 #pragma intrinsic(_BitScanForward)
  56 #endif
  57 
  58 inline unsigned count_trailing_zeros(uintx x) {
  59   assert(x != 0, "precondition");
  60   unsigned long index;
  61 #ifdef _LP64
  62   _BitScanForward64(&index, x);
  63 #else
  64   _BitScanForward(&index, x);
  65 #endif
  66   return index;
  67 }
  68 
  69 //////////////////////////////////////////////////////////////////////////////
  70 #elif defined(TARGET_COMPILER_xlc)
  71 
  72 #include <builtins.h>
  73 
  74 inline unsigned count_trailing_zeros(uintx x) {
  75   assert(x != 0, "precondition");
  76 #ifdef _LP64
  77   return __cnttz8(x);
  78 #else
  79   return __cnttz4(x);
  80 #endif
  81 }
  82 
  83 //////////////////////////////////////////////////////////////////////////////
  84 #elif defined(TARGET_COMPILER_sparcWorks)
  85 
  86 #include "utilities/macros.hpp"
  87 
  88 #include OS_CPU_HEADER(count_trailing_zeros)
  89 
  90 //////////////////////////////////////////////////////////////////////////////
  91 #else
  92 #error Unknown TARGET_COMPILER
  93 
  94 #endif // Toolchain dispatch
  95 
  96 #endif // include guard