LXR qemu/disas/libvixl/vixl/compiler-intrinsics.cc

   1// Copyright 2015, ARM Limited
   2// All rights reserved.
   3//
   4// Redistribution and use in source and binary forms, with or without
   5// modification, are permitted provided that the following conditions are met:
   6//
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   8//     this list of conditions and the following disclaimer.
   9//   * Redistributions in binary form must reproduce the above copyright notice,
  10//     this list of conditions and the following disclaimer in the documentation
  11//     and/or other materials provided with the distribution.
  12//   * Neither the name of ARM Limited nor the names of its contributors may be
  13//     used to endorse or promote products derived from this software without
  14//     specific prior written permission.
  15//
  16// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS CONTRIBUTORS "AS IS" AND
  17// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  18// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  19// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
  20// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  22// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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  25// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26
  27#include "compiler-intrinsics.h"
  28
  29namespace vixl {
  30
  31
  32int CountLeadingSignBitsFallBack(int64_t value, int width) {
  33  VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
  34  if (value >= 0) {
  35    return CountLeadingZeros(value, width) - 1;
  36  } else {
  37    return CountLeadingZeros(~value, width) - 1;
  38  }
  39}
  40
  41
  42int CountLeadingZerosFallBack(uint64_t value, int width) {
  43  VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
  44  if (value == 0) {
  45    return width;
  46  }
  47  int count = 0;
  48  value = value << (64 - width);
  49  if ((value & UINT64_C(0xffffffff00000000)) == 0) {
  50    count += 32;
  51    value = value << 32;
  52  }
  53  if ((value & UINT64_C(0xffff000000000000)) == 0) {
  54    count += 16;
  55    value = value << 16;
  56  }
  57  if ((value & UINT64_C(0xff00000000000000)) == 0) {
  58    count += 8;
  59    value = value << 8;
  60  }
  61  if ((value & UINT64_C(0xf000000000000000)) == 0) {
  62    count += 4;
  63    value = value << 4;
  64  }
  65  if ((value & UINT64_C(0xc000000000000000)) == 0) {
  66    count += 2;
  67    value = value << 2;
  68  }
  69  if ((value & UINT64_C(0x8000000000000000)) == 0) {
  70    count += 1;
  71  }
  72  count += (value == 0);
  73  return count;
  74}
  75
  76
  77int CountSetBitsFallBack(uint64_t value, int width) {
  78  VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
  79
  80  // Mask out unused bits to ensure that they are not counted.
  81  value &= (UINT64_C(0xffffffffffffffff) >> (64 - width));
  82
  83  // Add up the set bits.
  84  // The algorithm works by adding pairs of bit fields together iteratively,
  85  // where the size of each bit field doubles each time.
  86  // An example for an 8-bit value:
  87  // Bits:  h  g  f  e  d  c  b  a
  88  //         \ |   \ |   \ |   \ |
  89  // value = h+g   f+e   d+c   b+a
  90  //            \    |      \    |
  91  // value =   h+g+f+e     d+c+b+a
  92  //                  \          |
  93  // value =       h+g+f+e+d+c+b+a
  94  const uint64_t kMasks[] = {
  95    UINT64_C(0x5555555555555555),
  96    UINT64_C(0x3333333333333333),
  97    UINT64_C(0x0f0f0f0f0f0f0f0f),
  98    UINT64_C(0x00ff00ff00ff00ff),
  99    UINT64_C(0x0000ffff0000ffff),
 100    UINT64_C(0x00000000ffffffff),
 101  };
 102
 103  for (unsigned i = 0; i < (sizeof(kMasks) / sizeof(kMasks[0])); i++) {
 104    int shift = 1 << i;
 105    value = ((value >> shift) & kMasks[i]) + (value & kMasks[i]);
 106  }
 107
 108  return static_cast<int>(value);
 109}
 110
 111
 112int CountTrailingZerosFallBack(uint64_t value, int width) {
 113  VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
 114  int count = 0;
 115  value = value << (64 - width);
 116  if ((value & UINT64_C(0xffffffff)) == 0) {
 117    count += 32;
 118    value = value >> 32;
 119  }
 120  if ((value & 0xffff) == 0) {
 121    count += 16;
 122    value = value >> 16;
 123  }
 124  if ((value & 0xff) == 0) {
 125    count += 8;
 126    value = value >> 8;
 127  }
 128  if ((value & 0xf) == 0) {
 129    count += 4;
 130    value = value >> 4;
 131  }
 132  if ((value & 0x3) == 0) {
 133    count += 2;
 134    value = value >> 2;
 135  }
 136  if ((value & 0x1) == 0) {
 137    count += 1;
 138  }
 139  count += (value == 0);
 140  return count - (64 - width);
 141}
 142
 143
 144}  // namespace vixl
 145