diff options
| -rw-r--r-- | src/wasm-binary.h | 30 |
1 files changed, 23 insertions, 7 deletions
diff --git a/src/wasm-binary.h b/src/wasm-binary.h index 89073b8be..53afb6028 100644 --- a/src/wasm-binary.h +++ b/src/wasm-binary.h @@ -21,6 +21,7 @@ #ifndef wasm_wasm_binary_h #define wasm_wasm_binary_h +#include <cassert> #include <istream> #include <ostream> #include <type_traits> @@ -37,6 +38,8 @@ namespace wasm { template<typename T, typename MiniT> struct LEB { + static_assert(sizeof(MiniT) == 1, "MiniT must be a byte"); + T value; LEB() {} @@ -77,24 +80,37 @@ struct LEB { } while (more); } - void read(std::function<MiniT ()> get) { + void read(std::function<MiniT()> get) { value = 0; T shift = 0; MiniT byte; while (1) { byte = get(); - value |= ((T(byte & 127)) << shift); - if (!(byte & 128)) break; + bool last = !(byte & 128); + T payload = byte & 127; + typedef typename std::make_unsigned<T>::type mask_type; + auto shift_mask = 0 == shift + ? ~mask_type(0) + : ((mask_type(1) << (sizeof(T) * 8 - shift)) - 1u); + T significant_payload = payload & shift_mask; + if (significant_payload != payload) { + assert(std::is_signed<T>::value && last && + "dropped bits only valid for signed LEB"); + } + value |= significant_payload << shift; + if (last) break; shift += 7; + assert(size_t(shift) < sizeof(T) * 8 && "LEB overflow"); } - // if signed LEB, then we might need to sign-extend. (compile should optimize this out if not needed) + // If signed LEB, then we might need to sign-extend. (compile should + // optimize this out if not needed). if (std::is_signed<T>::value) { shift += 7; - if (byte & 64 && size_t(shift) < 8*sizeof(T)) { - size_t sext_bits = 8*sizeof(T) - size_t(shift); + if ((byte & 64) && size_t(shift) < 8 * sizeof(T)) { + size_t sext_bits = 8 * sizeof(T) - size_t(shift); value <<= sext_bits; value >>= sext_bits; - assert(value < 0); + assert(value < 0 && "sign-extend should produces a negative value"); } } } |