Home | History | Annotate | Download | only in src 
      1 // Copyright 2015, VIXL authors
      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-vixl.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
    145