| // Copyright 2011 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef V8_MISC_INTRINSICS_H_ |
| #define V8_MISC_INTRINSICS_H_ |
| |
| #include "include/v8.h" |
| #include "src/globals.h" |
| |
| namespace v8 { |
| namespace internal { |
| |
| // Returns the index of the leading 1 bit, counting the least significant bit at |
| // index 0. (1 << IntegerLog2(x)) is a mask for the most significant bit of x. |
| // Result is undefined if input is zero. |
| int IntegerLog2(uint32_t value); |
| |
| #if defined(__GNUC__) |
| |
| inline int IntegerLog2(uint32_t value) { |
| return 31 - __builtin_clz(value); |
| } |
| |
| #elif defined(_MSC_VER) |
| |
| #pragma intrinsic(_BitScanReverse) |
| |
| inline int IntegerLog2(uint32_t value) { |
| unsigned long result; // NOLINT: MSVC intrinsic demands this type. |
| _BitScanReverse(&result, value); |
| return result; |
| } |
| |
| #else |
| |
| // Default version using regular operations. Code taken from: |
| // http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog |
| inline int IntegerLog2(uint32_t value) { |
| int result, shift; |
| |
| shift = (value > 0xFFFF) << 4; |
| value >>= shift; |
| result = shift; |
| |
| shift = (value > 0xFF) << 3; |
| value >>= shift; |
| result |= shift; |
| |
| shift = (value > 0xF) << 2; |
| value >>= shift; |
| result |= shift; |
| |
| shift = (value > 0x3) << 1; |
| value >>= shift; |
| result |= shift; |
| |
| result |= (value >> 1); |
| |
| return result; |
| } |
| #endif |
| |
| } } // namespace v8::internal |
| |
| #endif // V8_MISC_INTRINSICS_H_ |