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Copy pathLEB128.cpp
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94 lines (77 loc) · 2.16 KB
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/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/
#include <climits>
#include "hermes/Support/LEB128.h"
#include "llvh/Support/ErrorHandling.h"
#include "llvh/Support/LEB128.h"
#include "llvh/Support/raw_ostream.h"
namespace {
/**
* bits<T>::width
*
* The size, in bits, of the type `T`.
*/
template <typename T>
struct bits {
static constexpr size_t width = sizeof(T) * CHAR_BIT;
};
template <size_t B, typename T>
using bigger_signed_int = typename std::enable_if<
std::is_integral<T>::value && std::is_signed<T>::value &&
B <= bits<T>::width,
T>::type;
/**
* signExtend<B, T>
*
* Take a `B`-bit signed twos-complement integer stored in an integral type `T`
* wider than `B` bits and sign-extend it to the full width of `T`.
*/
template <size_t B, typename T>
inline bigger_signed_int<B, T> signExtend(const T allBits) {
struct {
T lowBits : B;
} s;
s.lowBits = allBits;
return s.lowBits;
}
} // anonymous namespace
namespace hermes {
void appendSignedLEB128(std::vector<uint8_t> &vector, int64_t value) {
llvh::SmallVector<char, 16> data;
llvh::raw_svector_ostream OS(data);
llvh::encodeSLEB128(value, OS);
// "Convert" from char to uint8_t.
for (int i = 0, e = data.size(); i < e; i++) {
vector.push_back((uint8_t)data[i]);
}
}
unsigned readSignedLEB128(
llvh::ArrayRef<uint8_t> data,
unsigned offset,
int64_t *output) {
unsigned size;
*output = llvh::decodeSLEB128(&data[offset], &size);
return size;
}
void encodeSLEB128(int32_t input, llvh::raw_ostream &os, size_t minBytes) {
constexpr size_t CAP = bits<int32_t>::width / 7 + 1;
assert(minBytes <= CAP);
uint8_t buf[CAP]{};
for (size_t i = 0; i < CAP; ++i) {
int8_t byte = signExtend<7>(input);
if (byte != input || i + 1 < minBytes) {
buf[i] = byte | 0x80;
input = signExtend<bits<int32_t>::width - 7>(input >> 7);
} else {
buf[i] = byte & ~0x80;
os.write(reinterpret_cast<char *>(buf), i + 1);
return;
}
}
llvm_unreachable("Input too wide.");
}
} // namespace hermes