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compiler-intrinsics.h
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27 
28 #ifndef V8_COMPILER_INTRINSICS_H_
29 #define V8_COMPILER_INTRINSICS_H_
30 
31 namespace v8 {
32 namespace internal {
33 
35  public:
36  // Returns number of zero bits preceding least significant 1 bit.
37  // Undefined for zero value.
38  INLINE(static int CountTrailingZeros(uint32_t value));
39 
40  // Returns number of zero bits following most significant 1 bit.
41  // Undefined for zero value.
42  INLINE(static int CountLeadingZeros(uint32_t value));
43 
44  // Returns the number of bits set.
45  INLINE(static int CountSetBits(uint32_t value));
46 };
47 
48 #ifdef __GNUC__
49 int CompilerIntrinsics::CountTrailingZeros(uint32_t value) {
50  return __builtin_ctz(value);
51 }
52 
53 int CompilerIntrinsics::CountLeadingZeros(uint32_t value) {
54  return __builtin_clz(value);
55 }
56 
57 int CompilerIntrinsics::CountSetBits(uint32_t value) {
58  return __builtin_popcount(value);
59 }
60 
61 #elif defined(_MSC_VER)
62 
63 #pragma intrinsic(_BitScanForward)
64 #pragma intrinsic(_BitScanReverse)
65 
66 int CompilerIntrinsics::CountTrailingZeros(uint32_t value) {
67  unsigned long result; //NOLINT
68  _BitScanForward(&result, static_cast<long>(value)); //NOLINT
69  return static_cast<int>(result);
70 }
71 
72 int CompilerIntrinsics::CountLeadingZeros(uint32_t value) {
73  unsigned long result; //NOLINT
74  _BitScanReverse(&result, static_cast<long>(value)); //NOLINT
75  return 31 - static_cast<int>(result);
76 }
77 
78 int CompilerIntrinsics::CountSetBits(uint32_t value) {
79  // Manually count set bits.
80  value = ((value >> 1) & 0x55555555) + (value & 0x55555555);
81  value = ((value >> 2) & 0x33333333) + (value & 0x33333333);
82  value = ((value >> 4) & 0x0f0f0f0f) + (value & 0x0f0f0f0f);
83  value = ((value >> 8) & 0x00ff00ff) + (value & 0x00ff00ff);
84  value = ((value >> 16) & 0x0000ffff) + (value & 0x0000ffff);
85  return value;
86 }
87 
88 #else
89 #error Unsupported compiler
90 #endif
91 
92 } } // namespace v8::internal
93 
94 #endif // V8_COMPILER_INTRINSICS_H_
INLINE(static int CountTrailingZeros(uint32_t value))