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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 
CountLeadingSignBitsFallBack(int64_t value,int width)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 
CountLeadingZerosFallBack(uint64_t value,int width)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 
CountSetBitsFallBack(uint64_t value,int width)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 
CountTrailingZerosFallBack(uint64_t value,int width)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