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
10 namespace v8 {
11 namespace internal {
12
13 #define __ assm->
14
15
CountLeadingZeros(uint64_t value,int width)16 int 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
CountLeadingSignBits(int64_t value,int width)29 int 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
CountTrailingZeros(uint64_t value,int width)40 int 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
CountSetBits(uint64_t value,int width)51 int 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 static_cast<int>(value);
78 }
79
80
LargestPowerOf2Divisor(uint64_t value)81 uint64_t LargestPowerOf2Divisor(uint64_t value) {
82 return value & -value;
83 }
84
85
MaskToBit(uint64_t mask)86 int MaskToBit(uint64_t mask) {
87 DCHECK(CountSetBits(mask, 64) == 1);
88 return CountTrailingZeros(mask, 64);
89 }
90
91
92 } // namespace internal
93 } // namespace v8
94
95 #endif // V8_TARGET_ARCH_ARM64
96