diff options
| -rw-r--r-- | runtime/base/bit_utils.h | 23 | ||||
| -rw-r--r-- | runtime/leb128.h | 4 |
2 files changed, 10 insertions, 17 deletions
diff --git a/runtime/base/bit_utils.h b/runtime/base/bit_utils.h index 332012bda9..6f45dc8209 100644 --- a/runtime/base/bit_utils.h +++ b/runtime/base/bit_utils.h @@ -29,28 +29,21 @@ namespace art { template<typename T> static constexpr int CLZ(T x) { static_assert(std::is_integral<T>::value, "T must be integral"); - static_assert(std::is_unsigned<T>::value, "T must be unsigned"); + // TODO: assert unsigned. There is currently many uses with signed values. static_assert(sizeof(T) <= sizeof(long long), // NOLINT [runtime/int] [4] "T too large, must be smaller than long long"); - return - DCHECK_CONSTEXPR(x != 0, "x must not be zero", T(0)) - (sizeof(T) == sizeof(uint32_t)) - ? __builtin_clz(x) - : __builtin_clzll(x); + return (sizeof(T) == sizeof(uint32_t)) + ? __builtin_clz(x) // TODO: __builtin_clz[ll] has undefined behavior for x=0 + : __builtin_clzll(x); } template<typename T> static constexpr int CTZ(T x) { static_assert(std::is_integral<T>::value, "T must be integral"); - // A similar check to the above does not make sense. It isn't as non-intuitive to ask for - // trailing zeros in a negative number, and the quick backends do this for immediate encodings. - static_assert(sizeof(T) <= sizeof(long long), // NOLINT [runtime/int] [4] - "T too large, must be smaller than long long"); - return - DCHECK_CONSTEXPR(x != 0, "x must not be zero", T(0)) - (sizeof(T) == sizeof(uint32_t)) - ? __builtin_ctz(x) - : __builtin_ctzll(x); + // TODO: assert unsigned. There is currently many uses with signed values. + return (sizeof(T) == sizeof(uint32_t)) + ? __builtin_ctz(x) + : __builtin_ctzll(x); } template<typename T> diff --git a/runtime/leb128.h b/runtime/leb128.h index 976936d639..14683d4063 100644 --- a/runtime/leb128.h +++ b/runtime/leb128.h @@ -101,7 +101,7 @@ static inline int32_t DecodeSignedLeb128(const uint8_t** data) { static inline uint32_t UnsignedLeb128Size(uint32_t data) { // bits_to_encode = (data != 0) ? 32 - CLZ(x) : 1 // 32 - CLZ(data | 1) // bytes = ceil(bits_to_encode / 7.0); // (6 + bits_to_encode) / 7 - uint32_t x = 6 + 32 - CLZ(data | 1U); + uint32_t x = 6 + 32 - CLZ(data | 1); // Division by 7 is done by (x * 37) >> 8 where 37 = ceil(256 / 7). // This works for 0 <= x < 256 / (7 * 37 - 256), i.e. 0 <= x <= 85. return (x * 37) >> 8; @@ -111,7 +111,7 @@ static inline uint32_t UnsignedLeb128Size(uint32_t data) { static inline uint32_t SignedLeb128Size(int32_t data) { // Like UnsignedLeb128Size(), but we need one bit beyond the highest bit that differs from sign. data = data ^ (data >> 31); - uint32_t x = 1 /* we need to encode the sign bit */ + 6 + 32 - CLZ(data | 1U); + uint32_t x = 1 /* we need to encode the sign bit */ + 6 + 32 - CLZ(data | 1); return (x * 37) >> 8; } |