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/*
* Copyright (c) 2020-2021, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/NumericLimits.h>
#include <AK/Stream.h>
#include <AK/Types.h>
namespace AK {
struct LEB128 {
template<typename StreamT, typename ValueType = size_t>
static bool read_unsigned(StreamT& stream, ValueType& result)
{
[[maybe_unused]] size_t backup_offset = 0;
if constexpr (requires { stream.offset(); })
backup_offset = stream.offset();
InputStream& input_stream { stream };
result = 0;
size_t num_bytes = 0;
while (true) {
if (input_stream.unreliable_eof()) {
if constexpr (requires { stream.seek(backup_offset); })
stream.seek(backup_offset);
input_stream.set_fatal_error();
return false;
}
u8 byte = 0;
input_stream >> byte;
if (input_stream.has_any_error())
return false;
ValueType masked_byte = byte & ~(1 << 7);
const bool shift_too_large_for_result = (num_bytes * 7 > sizeof(ValueType) * 8) && (masked_byte != 0);
const bool shift_too_large_for_byte = ((masked_byte << (num_bytes * 7)) >> (num_bytes * 7)) != masked_byte;
if (shift_too_large_for_result || shift_too_large_for_byte)
return false;
result = (result) | (masked_byte << (num_bytes * 7));
if (!(byte & (1 << 7)))
break;
++num_bytes;
}
return true;
}
template<typename StreamT, typename ValueType = ssize_t>
static bool read_signed(StreamT& stream, ValueType& result)
{
// Note: We read into a u64 to simplify the parsing logic;
// result is range checked into ValueType after parsing.
static_assert(sizeof(ValueType) <= sizeof(u64), "Error checking logic assumes 64 bits or less!");
[[maybe_unused]] size_t backup_offset = 0;
if constexpr (requires { stream.offset(); })
backup_offset = stream.offset();
InputStream& input_stream { stream };
i64 temp = 0;
size_t num_bytes = 0;
u8 byte = 0;
result = 0;
do {
if (input_stream.unreliable_eof()) {
if constexpr (requires { stream.seek(backup_offset); })
stream.seek(backup_offset);
input_stream.set_fatal_error();
return false;
}
input_stream >> byte;
if (input_stream.has_any_error())
return false;
// note: 64 bit assumptions!
u64 masked_byte = byte & ~(1 << 7);
const bool shift_too_large_for_result = (num_bytes * 7 >= 64) && (masked_byte != ((temp < 0) ? 0x7Fu : 0u));
const bool shift_too_large_for_byte = (num_bytes * 7) == 63 && masked_byte != 0x00 && masked_byte != 0x7Fu;
if (shift_too_large_for_result || shift_too_large_for_byte)
return false;
temp = (temp) | (masked_byte << (num_bytes * 7));
++num_bytes;
} while (byte & (1 << 7));
if ((num_bytes * 7) < 64 && (byte & 0x40)) {
// sign extend
temp |= ((u64)(-1) << (num_bytes * 7));
}
// Now that we've accumulated into an i64, make sure it fits into result
if constexpr (sizeof(ValueType) < sizeof(u64)) {
if (temp > NumericLimits<ValueType>::max() || temp < NumericLimits<ValueType>::min())
return false;
}
result = static_cast<ValueType>(temp);
return true;
}
};
}
using AK::LEB128;
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