clzll.h
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14 
15 #ifndef RAPIDJSON_CLZLL_H_
16 #define RAPIDJSON_CLZLL_H_
17 
18 #include "../rapidjson.h"
19 
20 #if defined(_MSC_VER)
21 #include <intrin.h>
22 #if defined(_WIN64)
23 #pragma intrinsic(_BitScanReverse64)
24 #else
25 #pragma intrinsic(_BitScanReverse)
26 #endif
27 #endif
28 
29 RAPIDJSON_NAMESPACE_BEGIN
30 namespace internal {
31 
32 #if (defined(__GNUC__) && __GNUC__ >= 4) || RAPIDJSON_HAS_BUILTIN(__builtin_clzll)
33 #define RAPIDJSON_CLZLL __builtin_clzll
34 #else
35 
36 inline uint32_t clzll(uint64_t x) {
37  // Passing 0 to __builtin_clzll is UB in GCC and results in an
38  // infinite loop in the software implementation.
39  RAPIDJSON_ASSERT(x != 0);
40 
41 #if defined(_MSC_VER)
42  unsigned long r = 0;
43 #if defined(_WIN64)
44  _BitScanReverse64(&r, x);
45 #else
46  // Scan the high 32 bits.
47  if (_BitScanReverse(&r, static_cast<uint32_t>(x >> 32)))
48  return 63 - (r + 32);
49 
50  // Scan the low 32 bits.
51  _BitScanReverse(&r, static_cast<uint32_t>(x & 0xFFFFFFFF));
52 #endif // _WIN64
53 
54  return 63 - r;
55 #else
56  uint32_t r;
57  while (!(x & (static_cast<uint64_t>(1) << 63))) {
58  x <<= 1;
59  ++r;
60  }
61 
62  return r;
63 #endif // _MSC_VER
64 }
65 
66 #define RAPIDJSON_CLZLL RAPIDJSON_NAMESPACE::internal::clzll
67 #endif // (defined(__GNUC__) && __GNUC__ >= 4) || RAPIDJSON_HAS_BUILTIN(__builtin_clzll)
68 
69 } // namespace internal
70 RAPIDJSON_NAMESPACE_END
71 
72 #endif // RAPIDJSON_CLZLL_H_
#define RAPIDJSON_ASSERT(x)
Assertion.
Definition: rapidjson.h:406