#pragma once
#include <algorithm>
#include <limits.h>
#include <wtf/Compiler.h>
namespace WTF { namespace LEBDecoder {
template<typename T>
constexpr size_t maxByteLength()
{
constexpr size_t numBits = sizeof(T) * CHAR_BIT;
return (numBits - 1) / 7 + 1; }
template<typename T>
constexpr unsigned lastByteMask()
{
constexpr size_t numBits = sizeof(T) * CHAR_BIT;
static_assert(numBits % 7);
return ~((1U << (numBits % 7)) - 1);
}
template<typename T>
inline bool WARN_UNUSED_RETURN decodeUInt(const uint8_t* bytes, size_t length, size_t& offset, T& result)
{
static_assert(std::is_unsigned_v<T>);
if (length <= offset)
return false;
result = 0;
unsigned shift = 0;
size_t last = std::min(maxByteLength<T>(), length - offset) - 1;
for (unsigned i = 0; true; ++i) {
uint8_t byte = bytes[offset++];
result |= static_cast<T>(byte & 0x7f) << shift;
shift += 7;
if (!(byte & 0x80))
return !(((maxByteLength<T>() - 1) == i && (byte & lastByteMask<T>())));
if (i == last)
return false;
}
RELEASE_ASSERT_NOT_REACHED();
return true;
}
template<typename T>
inline bool WARN_UNUSED_RETURN decodeInt(const uint8_t* bytes, size_t length, size_t& offset, T& result)
{
static_assert(std::is_signed_v<T>);
if (length <= offset)
return false;
using UnsignedT = typename std::make_unsigned<T>::type;
result = 0;
unsigned shift = 0;
size_t last = std::min(maxByteLength<T>(), length - offset) - 1;
uint8_t byte;
for (unsigned i = 0; true; ++i) {
byte = bytes[offset++];
result |= static_cast<T>(static_cast<UnsignedT>(byte & 0x7f) << shift);
shift += 7;
if (!(byte & 0x80)) {
if ((maxByteLength<T>() - 1) == i) {
if (!(byte & 0x40)) {
if (byte & (lastByteMask<T>() >> 1))
return false;
} else {
if (static_cast<uint8_t>(~(byte | 0x80)) & (lastByteMask<T>() >> 1))
return false;
}
}
break;
}
if (i == last)
return false;
}
const size_t numBits = sizeof(T) * CHAR_BIT;
if (shift < numBits && (byte & 0x40))
result = static_cast<T>(static_cast<UnsignedT>(result) | (static_cast<UnsignedT>(-1) << shift));
return true;
}
inline bool WARN_UNUSED_RETURN decodeUInt32(const uint8_t* bytes, size_t length, size_t& offset, uint32_t& result)
{
return decodeUInt<uint32_t>(bytes, length, offset, result);
}
inline bool WARN_UNUSED_RETURN decodeUInt64(const uint8_t* bytes, size_t length, size_t& offset, uint64_t& result)
{
return decodeUInt<uint64_t>(bytes, length, offset, result);
}
inline bool WARN_UNUSED_RETURN decodeInt32(const uint8_t* bytes, size_t length, size_t& offset, int32_t& result)
{
return decodeInt<int32_t>(bytes, length, offset, result);
}
inline bool WARN_UNUSED_RETURN decodeInt64(const uint8_t* bytes, size_t length, size_t& offset, int64_t& result)
{
return decodeInt<int64_t>(bytes, length, offset, result);
}
} }