1// Copyright 2013 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#if V8_TARGET_ARCH_ARM64
6
7#include "src/arm64/utils-arm64.h"
8
9
10namespace v8 {
11namespace internal {
12
13#define __ assm->
14
15
16int CountLeadingZeros(uint64_t value, int width) {
17  // TODO(jbramley): Optimize this for ARM64 hosts.
18  DCHECK((width == 32) || (width == 64));
19  int count = 0;
20  uint64_t bit_test = 1UL << (width - 1);
21  while ((count < width) && ((bit_test & value) == 0)) {
22    count++;
23    bit_test >>= 1;
24  }
25  return count;
26}
27
28
29int CountLeadingSignBits(int64_t value, int width) {
30  // TODO(jbramley): Optimize this for ARM64 hosts.
31  DCHECK((width == 32) || (width == 64));
32  if (value >= 0) {
33    return CountLeadingZeros(value, width) - 1;
34  } else {
35    return CountLeadingZeros(~value, width) - 1;
36  }
37}
38
39
40int CountTrailingZeros(uint64_t value, int width) {
41  // TODO(jbramley): Optimize this for ARM64 hosts.
42  DCHECK((width == 32) || (width == 64));
43  int count = 0;
44  while ((count < width) && (((value >> count) & 1) == 0)) {
45    count++;
46  }
47  return count;
48}
49
50
51int CountSetBits(uint64_t value, int width) {
52  // TODO(jbramley): Would it be useful to allow other widths? The
53  // implementation already supports them.
54  DCHECK((width == 32) || (width == 64));
55
56  // Mask out unused bits to ensure that they are not counted.
57  value &= (0xffffffffffffffffUL >> (64-width));
58
59  // Add up the set bits.
60  // The algorithm works by adding pairs of bit fields together iteratively,
61  // where the size of each bit field doubles each time.
62  // An example for an 8-bit value:
63  // Bits:  h  g  f  e  d  c  b  a
64  //         \ |   \ |   \ |   \ |
65  // value = h+g   f+e   d+c   b+a
66  //            \    |      \    |
67  // value =   h+g+f+e     d+c+b+a
68  //                  \          |
69  // value =       h+g+f+e+d+c+b+a
70  value = ((value >> 1) & 0x5555555555555555) + (value & 0x5555555555555555);
71  value = ((value >> 2) & 0x3333333333333333) + (value & 0x3333333333333333);
72  value = ((value >> 4) & 0x0f0f0f0f0f0f0f0f) + (value & 0x0f0f0f0f0f0f0f0f);
73  value = ((value >> 8) & 0x00ff00ff00ff00ff) + (value & 0x00ff00ff00ff00ff);
74  value = ((value >> 16) & 0x0000ffff0000ffff) + (value & 0x0000ffff0000ffff);
75  value = ((value >> 32) & 0x00000000ffffffff) + (value & 0x00000000ffffffff);
76
77  return value;
78}
79
80
81uint64_t LargestPowerOf2Divisor(uint64_t value) {
82  return value & -value;
83}
84
85
86int MaskToBit(uint64_t mask) {
87  DCHECK(CountSetBits(mask, 64) == 1);
88  return CountTrailingZeros(mask, 64);
89}
90
91
92} }  // namespace v8::internal
93
94#endif  // V8_TARGET_ARCH_ARM64
95