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//===- BinaryItemStream.h ---------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_BINARYITEMSTREAM_H
#define LLVM_SUPPORT_BINARYITEMSTREAM_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/Support/BinaryStream.h"
#include "llvm/Support/BinaryStreamError.h"
#include "llvm/Support/Error.h"
#include <cstddef>
#include <cstdint>
namespace llvm {
template <typename T> struct BinaryItemTraits {
static size_t length(const T &Item) = delete;
static ArrayRef<uint8_t> bytes(const T &Item) = delete;
};
/// BinaryItemStream represents a sequence of objects stored in some kind of
/// external container but for which it is useful to view as a stream of
/// contiguous bytes. An example of this might be if you have a collection of
/// records and you serialize each one into a buffer, and store these serialized
/// records in a container. The pointers themselves are not laid out
/// contiguously in memory, but we may wish to read from or write to these
/// records as if they were.
template <typename T, typename Traits = BinaryItemTraits<T>>
class BinaryItemStream : public BinaryStream {
public:
explicit BinaryItemStream(llvm::endianness Endian) : Endian(Endian) {}
llvm::endianness getEndian() const override { return Endian; }
Error readBytes(uint64_t Offset, uint64_t Size,
ArrayRef<uint8_t> &Buffer) override {
auto ExpectedIndex = translateOffsetIndex(Offset);
if (!ExpectedIndex)
return ExpectedIndex.takeError();
const auto &Item = Items[*ExpectedIndex];
if (auto EC = checkOffsetForRead(Offset, Size))
return EC;
if (Size > Traits::length(Item))
return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
Buffer = Traits::bytes(Item).take_front(Size);
return Error::success();
}
Error readLongestContiguousChunk(uint64_t Offset,
ArrayRef<uint8_t> &Buffer) override {
auto ExpectedIndex = translateOffsetIndex(Offset);
if (!ExpectedIndex)
return ExpectedIndex.takeError();
Buffer = Traits::bytes(Items[*ExpectedIndex]);
return Error::success();
}
void setItems(ArrayRef<T> ItemArray) {
Items = ItemArray;
computeItemOffsets();
}
uint64_t getLength() override {
return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back();
}
private:
void computeItemOffsets() {
ItemEndOffsets.clear();
ItemEndOffsets.reserve(Items.size());
uint64_t CurrentOffset = 0;
for (const auto &Item : Items) {
uint64_t Len = Traits::length(Item);
assert(Len > 0 && "no empty items");
CurrentOffset += Len;
ItemEndOffsets.push_back(CurrentOffset);
}
}
Expected<uint32_t> translateOffsetIndex(uint64_t Offset) {
// Make sure the offset is somewhere in our items array.
if (Offset >= getLength())
return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
++Offset;
auto Iter = llvm::lower_bound(ItemEndOffsets, Offset);
size_t Idx = std::distance(ItemEndOffsets.begin(), Iter);
assert(Idx < Items.size() && "binary search for offset failed");
return Idx;
}
llvm::endianness Endian;
ArrayRef<T> Items;
// Sorted vector of offsets to accelerate lookup.
std::vector<uint64_t> ItemEndOffsets;
};
} // end namespace llvm
#endif // LLVM_SUPPORT_BINARYITEMSTREAM_H
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