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 //
   7 //   * Redistributions of source code must retain the above copyright notice,
   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
  23 // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  24 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  25 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26
  27 #include "compiler-intrinsics.h"
  28
  29 namespace vixl {
  30
  31
  32 int 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
  42 int 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
  77 int 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
 112 int 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