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//===- StringTableStreamBuilder.cpp - PDB String Table ----------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/DebugInfo/PDB/Native/StringTableStreamBuilder.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/DebugInfo/PDB/Native/Hash.h"
#include "llvm/DebugInfo/PDB/Native/RawTypes.h"
#include "llvm/Support/BinaryStreamWriter.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
using namespace llvm::support;
using namespace llvm::support::endian;
using namespace llvm::pdb;
uint32_t StringTableStreamBuilder::insert(StringRef S) {
return Strings.insert(S);
}
static uint32_t computeBucketCount(uint32_t NumStrings) {
// The /names stream is basically an on-disk open-addressing hash table.
// Hash collisions are resolved by linear probing. We cannot make
// utilization 100% because it will make the linear probing extremely
// slow. But lower utilization wastes disk space. As a reasonable
// load factor, we choose 80%. We need +1 because slot 0 is reserved.
return (NumStrings + 1) * 1.25;
}
uint32_t StringTableStreamBuilder::hashTableSize() const {
uint32_t Size = sizeof(uint32_t); // Hash table begins with 4-byte size field.
Size += computeBucketCount(Strings.size()) * sizeof(uint32_t);
return Size;
}
uint32_t StringTableStreamBuilder::calculateSerializedSize() const {
uint32_t Size = 0;
Size += sizeof(StringTableHeader);
Size += Strings.calculateSerializedSize();
Size += hashTableSize();
Size += sizeof(uint32_t); // The table ends with the number of strings.
return Size;
}
Error StringTableStreamBuilder::writeHeader(BinaryStreamWriter &Writer) const {
// Write a header
StringTableHeader H;
H.Signature = StringTableSignature;
H.HashVersion = 1;
H.ByteSize = Strings.calculateSerializedSize();
if (auto EC = Writer.writeObject(H))
return EC;
assert(Writer.bytesRemaining() == 0);
return Error::success();
}
Error StringTableStreamBuilder::writeStrings(BinaryStreamWriter &Writer) const {
if (auto EC = Strings.commit(Writer))
return EC;
assert(Writer.bytesRemaining() == 0);
return Error::success();
}
Error StringTableStreamBuilder::writeHashTable(
BinaryStreamWriter &Writer) const {
// Write a hash table.
uint32_t BucketCount = computeBucketCount(Strings.size());
if (auto EC = Writer.writeInteger(BucketCount))
return EC;
std::vector<ulittle32_t> Buckets(BucketCount);
for (auto &Pair : Strings) {
StringRef S = Pair.getKey();
uint32_t Offset = Pair.getValue();
uint32_t Hash = hashStringV1(S);
for (uint32_t I = 0; I != BucketCount; ++I) {
uint32_t Slot = (Hash + I) % BucketCount;
if (Slot == 0)
continue; // Skip reserved slot
if (Buckets[Slot] != 0)
continue;
Buckets[Slot] = Offset;
break;
}
}
if (auto EC = Writer.writeArray(makeArrayRef(Buckets)))
return EC;
assert(Writer.bytesRemaining() == 0);
return Error::success();
}
Error StringTableStreamBuilder::commit(BinaryStreamWriter &Writer) const {
BinaryStreamWriter Section;
std::tie(Section, Writer) = Writer.split(sizeof(StringTableHeader));
if (auto EC = writeHeader(Section))
return EC;
std::tie(Section, Writer) = Writer.split(Strings.calculateSerializedSize());
if (auto EC = writeStrings(Section))
return EC;
std::tie(Section, Writer) = Writer.split(hashTableSize());
if (auto EC = writeHashTable(Section))
return EC;
if (auto EC = Writer.writeInteger<uint32_t>(Strings.size()))
return EC;
assert(Writer.bytesRemaining() == 0);
return Error::success();
}
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