- abe587c2360b21f085b7d65a77d840015bc04cf6 Factor an internal interface into its own header, as it w... by Greg Falcon <gfalcon@google.com>

  - 2201f1644336e64280dbd20207d8fbc3bfea2bf4 Internal change. by Abseil Team <absl-team@google.com>
  - 94e6b5b20d2cc754c99a18c575a4f1f3cd1f28d4 Rename no_throw_ctor to nothrow_ctor to match the standar... by Abseil Team <absl-team@google.com>
  - 86aa34d2129c4914c5133b7b619480aae786288e Update header files in debugging target by Tom Manshreck <shreck@google.com>
  - ed234519ced458724a7267b8fdf184eaae1c97c7 Remove CMAKE_CXX_WARNING_VLA from our c++ flags in the cm... by Jon Cohen <cohenjon@google.com>

GitOrigin-RevId: abe587c2360b21f085b7d65a77d840015bc04cf6
Change-Id: I92f9301c69419d3830c358b88984967185aa33f6

1 files changed, 53 insertions, 0 deletions

diff --git a/absl/strings/internal/bits.h b/absl/strings/internal/bits.h
new file mode 100644
index 000000000000..901082ccddfc
--- /dev/null
+++ b/absl/strings/internal/bits.h
@@ -0,0 +1,53 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// 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 ABSL_STRINGS_INTERNAL_BITS_H_
+#define ABSL_STRINGS_INTERNAL_BITS_H_
+
+#include <cstdint>
+
+#if defined(_MSC_VER) && defined(_M_X64)
+#include <intrin.h>
+#pragma intrinsic(_BitScanReverse64)
+#endif
+
+namespace absl {
+namespace strings_internal {
+
+// Returns the number of leading 0 bits in a 64-bit value.
+inline int CountLeadingZeros64(uint64_t n) {
+#if defined(__GNUC__)
+  static_assert(sizeof(unsigned long long) == sizeof(n),  // NOLINT(runtime/int)
+                "__builtin_clzll does not take 64bit arg");
+  return n == 0 ? 64 : __builtin_clzll(n);
+#elif defined(_MSC_VER) && defined(_M_X64)
+  unsigned long result;  // NOLINT(runtime/int)
+  if (_BitScanReverse64(&result, n)) {
+    return 63 - result;
+  }
+  return 64;
+#else
+  int zeroes = 60;
+  if (n >> 32) zeroes -= 32, n >>= 32;
+  if (n >> 16) zeroes -= 16, n >>= 16;
+  if (n >> 8) zeroes -= 8, n >>= 8;
+  if (n >> 4) zeroes -= 4, n >>= 4;
+  return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0\0"[n] + zeroes;
+#endif
+}
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_BITS_H_