1 files changed, 71 insertions, 0 deletions
diff --git a/include/rapidjson/internal/clzll.h b/include/rapidjson/internal/clzll.h
new file mode 100644
index 0000000..8fc5118
--- /dev/null
+++ b/include/rapidjson/internal/clzll.h
@@ -0,0 +1,71 @@
+// Tencent is pleased to support the open source community by making RapidJSON available.
+//
+// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.
+//
+// Licensed under the MIT License (the "License"); you may not use this file except
+// in compliance with the License. You may obtain a copy of the License at
+//
+// http://opensource.org/licenses/MIT
+//
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+#ifndef RAPIDJSON_CLZLL_H_
+#define RAPIDJSON_CLZLL_H_
+
+#include "../rapidjson.h"
+
+#if defined(_MSC_VER) && !defined(UNDER_CE)
+#include <intrin.h>
+#if defined(_WIN64)
+#pragma intrinsic(_BitScanReverse64)
+#else
+#pragma intrinsic(_BitScanReverse)
+#endif
+#endif
+
+RAPIDJSON_NAMESPACE_BEGIN
+namespace internal {
+
+inline uint32_t clzll(uint64_t x) {
+    // Passing 0 to __builtin_clzll is UB in GCC and results in an
+    // infinite loop in the software implementation.
+    RAPIDJSON_ASSERT(x != 0);
+
+#if defined(_MSC_VER) && !defined(UNDER_CE)
+    unsigned long r = 0;
+#if defined(_WIN64)
+    _BitScanReverse64(&r, x);
+#else
+    // Scan the high 32 bits.
+    if (_BitScanReverse(&r, static_cast<uint32_t>(x >> 32)))
+        return 63 - (r + 32);
+
+    // Scan the low 32 bits.
+    _BitScanReverse(&r, static_cast<uint32_t>(x & 0xFFFFFFFF));
+#endif // _WIN64
+
+    return 63 - r;
+#elif (defined(__GNUC__) && __GNUC__ >= 4) || RAPIDJSON_HAS_BUILTIN(__builtin_clzll)
+    // __builtin_clzll wrapper
+    return static_cast<uint32_t>(__builtin_clzll(x));
+#else
+    // naive version
+    uint32_t r = 0;
+    while (!(x & (static_cast<uint64_t>(1) << 63))) {
+        x <<= 1;
+        ++r;
+    }
+
+    return r;
+#endif // _MSC_VER
+}
+
+#define RAPIDJSON_CLZLL RAPIDJSON_NAMESPACE::internal::clzll
+
+} // namespace internal
+RAPIDJSON_NAMESPACE_END
+
+#endif // RAPIDJSON_CLZLL_H_