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 #include "utils-vixl.h"
30
31 namespace vixl {
32
33
CountLeadingSignBitsFallBack(int64_t value, int width)34 int CountLeadingSignBitsFallBack(int64_t value, int width) {
35 VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
36 if (width < 64) VIXL_ASSERT(IsIntN(width, value));
37 if (value >= 0) {
38 return CountLeadingZeros(value, width) - 1;
39 } else {
40 return CountLeadingZeros(~value, width) - 1;
41 }
42 }
43
44
CountLeadingZerosFallBack(uint64_t value, int width)45 int CountLeadingZerosFallBack(uint64_t value, int width) {
46 VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
47 if (value == 0) {
48 return width;
49 }
50 int count = 0;
51 value = value << (64 - width);
52 if ((value & UINT64_C(0xffffffff00000000)) == 0) {
53 count += 32;
54 value = value << 32;
55 }
56 if ((value & UINT64_C(0xffff000000000000)) == 0) {
57 count += 16;
58 value = value << 16;
59 }
60 if ((value & UINT64_C(0xff00000000000000)) == 0) {
61 count += 8;
62 value = value << 8;
63 }
64 if ((value & UINT64_C(0xf000000000000000)) == 0) {
65 count += 4;
66 value = value << 4;
67 }
68 if ((value & UINT64_C(0xc000000000000000)) == 0) {
69 count += 2;
70 value = value << 2;
71 }
72 if ((value & UINT64_C(0x8000000000000000)) == 0) {
73 count += 1;
74 }
75 count += (value == 0);
76 return count;
77 }
78
79
CountSetBitsFallBack(uint64_t value, int width)80 int CountSetBitsFallBack(uint64_t value, int width) {
81 VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
82
83 // Mask out unused bits to ensure that they are not counted.
84 value &= (UINT64_C(0xffffffffffffffff) >> (64 - width));
85
86 // Add up the set bits.
87 // The algorithm works by adding pairs of bit fields together iteratively,
88 // where the size of each bit field doubles each time.
89 // An example for an 8-bit value:
90 // Bits: h g f e d c b a
91 // \ | \ | \ | \ |
92 // value = h+g f+e d+c b+a
93 // \ | \ |
94 // value = h+g+f+e d+c+b+a
95 // \ |
96 // value = h+g+f+e+d+c+b+a
97 const uint64_t kMasks[] = {
98 UINT64_C(0x5555555555555555),
99 UINT64_C(0x3333333333333333),
100 UINT64_C(0x0f0f0f0f0f0f0f0f),
101 UINT64_C(0x00ff00ff00ff00ff),
102 UINT64_C(0x0000ffff0000ffff),
103 UINT64_C(0x00000000ffffffff),
104 };
105
106 for (unsigned i = 0; i < (sizeof(kMasks) / sizeof(kMasks[0])); i++) {
107 int shift = 1 << i;
108 value = ((value >> shift) & kMasks[i]) + (value & kMasks[i]);
109 }
110
111 return static_cast<int>(value);
112 }
113
114
CountTrailingZerosFallBack(uint64_t value, int width)115 int CountTrailingZerosFallBack(uint64_t value, int width) {
116 VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
117 int count = 0;
118 value = value << (64 - width);
119 if ((value & UINT64_C(0xffffffff)) == 0) {
120 count += 32;
121 value = value >> 32;
122 }
123 if ((value & 0xffff) == 0) {
124 count += 16;
125 value = value >> 16;
126 }
127 if ((value & 0xff) == 0) {
128 count += 8;
129 value = value >> 8;
130 }
131 if ((value & 0xf) == 0) {
132 count += 4;
133 value = value >> 4;
134 }
135 if ((value & 0x3) == 0) {
136 count += 2;
137 value = value >> 2;
138 }
139 if ((value & 0x1) == 0) {
140 count += 1;
141 }
142 count += (value == 0);
143 return count - (64 - width);
144 }
145
146
147 } // namespace vixl
148