disas/libvixl/utils.cc

   1 // Copyright 2013, 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 "utils.h"
  28 #include <stdio.h>
  29
  30 namespace vixl {
  31
  32 uint32_t float_to_rawbits(float value) {
  33   uint32_t bits = 0;
  34   memcpy(&bits, &value, 4);
  35   return bits;
  36 }
  37
  38
  39 uint64_t double_to_rawbits(double value) {
  40   uint64_t bits = 0;
  41   memcpy(&bits, &value, 8);
  42   return bits;
  43 }
  44
  45
  46 float rawbits_to_float(uint32_t bits) {
  47   float value = 0.0;
  48   memcpy(&value, &bits, 4);
  49   return value;
  50 }
  51
  52
  53 double rawbits_to_double(uint64_t bits) {
  54   double value = 0.0;
  55   memcpy(&value, &bits, 8);
  56   return value;
  57 }
  58
  59
  60 int CountLeadingZeros(uint64_t value, int width) {
  61   VIXL_ASSERT((width == 32) || (width == 64));
  62   int count = 0;
  63   uint64_t bit_test = UINT64_C(1) << (width - 1);
  64   while ((count < width) && ((bit_test & value) == 0)) {
  65     count++;
  66     bit_test >>= 1;
  67   }
  68   return count;
  69 }
  70
  71
  72 int CountLeadingSignBits(int64_t value, int width) {
  73   VIXL_ASSERT((width == 32) || (width == 64));
  74   if (value >= 0) {
  75     return CountLeadingZeros(value, width) - 1;
  76   } else {
  77     return CountLeadingZeros(~value, width) - 1;
  78   }
  79 }
  80
  81
  82 int CountTrailingZeros(uint64_t value, int width) {
  83   VIXL_ASSERT((width == 32) || (width == 64));
  84   int count = 0;
  85   while ((count < width) && (((value >> count) & 1) == 0)) {
  86     count++;
  87   }
  88   return count;
  89 }
  90
  91
  92 int CountSetBits(uint64_t value, int width) {
  93   // TODO: Other widths could be added here, as the implementation already
  94   // supports them.
  95   VIXL_ASSERT((width == 32) || (width == 64));
  96
  97   // Mask out unused bits to ensure that they are not counted.
  98   value &= (UINT64_C(0xffffffffffffffff) >> (64-width));
  99
 100   // Add up the set bits.
 101   // The algorithm works by adding pairs of bit fields together iteratively,
 102   // where the size of each bit field doubles each time.
 103   // An example for an 8-bit value:
 104   // Bits:  h  g  f  e  d  c  b  a
 105   //         \ |   \ |   \ |   \ |
 106   // value = h+g   f+e   d+c   b+a
 107   //            \    |      \    |
 108   // value =   h+g+f+e     d+c+b+a
 109   //                  \          |
 110   // value =       h+g+f+e+d+c+b+a
 111   const uint64_t kMasks[] = {
 112     UINT64_C(0x5555555555555555),
 113     UINT64_C(0x3333333333333333),
 114     UINT64_C(0x0f0f0f0f0f0f0f0f),
 115     UINT64_C(0x00ff00ff00ff00ff),
 116     UINT64_C(0x0000ffff0000ffff),
 117     UINT64_C(0x00000000ffffffff),
 118   };
 119
 120   for (unsigned i = 0; i < (sizeof(kMasks) / sizeof(kMasks[0])); i++) {
 121     int shift = 1 << i;
 122     value = ((value >> shift) & kMasks[i]) + (value & kMasks[i]);
 123   }
 124
 125   return value;
 126 }
 127
 128
 129 uint64_t LowestSetBit(uint64_t value) {
 130   return value & -value;
 131 }
 132
 133
 134 bool IsPowerOf2(int64_t value) {
 135   return (value != 0) && ((value & (value - 1)) == 0);
 136 }
 137
 138 }  // namespace vixl