hphp/vixl/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 "hphp/vixl/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   assert((width == 32) || (width == 64));
  62   int count = 0;
  63   uint64_t bit_test = 1UL << (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   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   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   assert((width == 32) || (width == 64));
  96
  97   // Mask out unused bits to ensure that they are not counted.
  98   value &= (0xffffffffffffffffUL >> (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   value = ((value >> 1) & 0x5555555555555555) + (value & 0x5555555555555555);
 112   value = ((value >> 2) & 0x3333333333333333) + (value & 0x3333333333333333);
 113   value = ((value >> 4) & 0x0f0f0f0f0f0f0f0f) + (value & 0x0f0f0f0f0f0f0f0f);
 114   value = ((value >> 8) & 0x00ff00ff00ff00ff) + (value & 0x00ff00ff00ff00ff);
 115   value = ((value >> 16) & 0x0000ffff0000ffff) + (value & 0x0000ffff0000ffff);
 116   value = ((value >> 32) & 0x00000000ffffffff) + (value & 0x00000000ffffffff);
 117
 118   return value;
 119 }
 120 }  // namespace vixl