include/llvm/Bitcode/NaCl/NaClBitstreamWriter.h - external/github.com/kripken/emscripten-fastcomp - Git at Google

 //===- NaClBitstreamWriter.h - NaCl bitstream writer ------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This header defines the BitstreamWriter class.  This class can be used to
 // write an arbitrary bitstream, regardless of its contents.
 //
 //===----------------------------------------------------------------------===//

 #ifndef LLVM_BITCODE_NACL_NACLBITSTREAMWRITER_H
 #define LLVM_BITCODE_NACL_NACLBITSTREAMWRITER_H

 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Bitcode/NaCl/NaClBitCodes.h"
 #include <vector>

 namespace llvm {

 class NaClBitstreamWriter {
   SmallVectorImpl<char> &Out;

   /// CurBit - Always between 0 and 31 inclusive, specifies the next bit to use.
   unsigned CurBit;

   /// CurValue - The current value.  Only bits < CurBit are valid.
   uint32_t CurValue;

   /// CurCodeSize - This is the declared size of code values used for the
   /// current block, in bits.
   NaClBitcodeSelectorAbbrev CurCodeSize;

   /// BlockInfoCurBID - When emitting a BLOCKINFO_BLOCK, this is the currently
   /// selected BLOCK ID.
   unsigned BlockInfoCurBID;

   /// CurAbbrevs - Abbrevs installed at in this block.
   std::vector<NaClBitCodeAbbrev*> CurAbbrevs;

   struct Block {
     NaClBitcodeSelectorAbbrev PrevCodeSize;
     unsigned StartSizeWord;
     std::vector<NaClBitCodeAbbrev*> PrevAbbrevs;
     Block(const NaClBitcodeSelectorAbbrev& PCS, unsigned SSW)
         : PrevCodeSize(PCS), StartSizeWord(SSW) {}
   };

   /// BlockScope - This tracks the current blocks that we have entered.
   std::vector<Block> BlockScope;

   /// BlockInfo - This contains information emitted to BLOCKINFO_BLOCK blocks.
   /// These describe abbreviations that all blocks of the specified ID inherit.
   struct BlockInfo {
     unsigned BlockID;
     std::vector<NaClBitCodeAbbrev*> Abbrevs;
   };
   std::vector<BlockInfo> BlockInfoRecords;

   /// AbbrevValues - Wrapper class that allows the bitstream writer to
   /// prefix a code to the set of values, associated with a record to
   /// emit, without having to destructively change the contents of
   /// values.
   template<typename uintty>
   struct AbbrevValues {
     AbbrevValues(uintty Code, const SmallVectorImpl<uintty> &Values)
         : Code(Code), Values(Values) {}

     size_t size() const {
       return Values.size() + 1;
     }

     uintty operator[](size_t Index) const {
       return Index == 0 ? Code : Values[Index-1];
     }

   private:
     // The code to use (if not DONT_USE_CODE).
     uintty Code;
     const SmallVectorImpl<uintty> &Values;
   };

 public:
   // BackpatchWord - Backpatch a 32-bit word in the output with the specified
   // value.
   void BackpatchWord(unsigned ByteNo, unsigned NewWord) {
     Out[ByteNo++] = (unsigned char)(NewWord >>  0);
     Out[ByteNo++] = (unsigned char)(NewWord >>  8);
     Out[ByteNo++] = (unsigned char)(NewWord >> 16);
     Out[ByteNo  ] = (unsigned char)(NewWord >> 24);
   }

 private:
   void WriteByte(unsigned char Value) {
     Out.push_back(Value);
   }

   void WriteWord(unsigned Value) {
     unsigned char Bytes[4] = {
       (unsigned char)(Value >>  0),
       (unsigned char)(Value >>  8),
       (unsigned char)(Value >> 16),
       (unsigned char)(Value >> 24) };
     Out.append(&Bytes[0], &Bytes[4]);
   }

   unsigned GetBufferOffset() const {
     return Out.size();
   }

   unsigned GetWordIndex() const {
     unsigned Offset = GetBufferOffset();
     assert((Offset & 3) == 0 && "Not 32-bit aligned");
     return Offset / 4;
   }

 public:
   explicit NaClBitstreamWriter(SmallVectorImpl<char> &O)
       : Out(O), CurBit(0), CurValue(0), CurCodeSize() {}

   ~NaClBitstreamWriter() {
     assert(CurBit == 0 && "Unflused data remaining");
     assert(BlockScope.empty() && CurAbbrevs.empty() && "Block imbalance");

     // Free the BlockInfoRecords.
     while (!BlockInfoRecords.empty()) {
       BlockInfo &Info = BlockInfoRecords.back();
       // Free blockinfo abbrev info.
       for (unsigned i = 0, e = static_cast<unsigned>(Info.Abbrevs.size());
            i != e; ++i)
         Info.Abbrevs[i]->dropRef();
       BlockInfoRecords.pop_back();
     }
   }

   /// \brief Retrieve the current position in the stream, in bits.
   uint64_t GetCurrentBitNo() const { return GetBufferOffset() * 8 + CurBit; }

   //===--------------------------------------------------------------------===//
   // Basic Primitives for emitting bits to the stream.
   //===--------------------------------------------------------------------===//

   void Emit(uint32_t Val, unsigned NumBits) {
     assert(NumBits && NumBits <= 32 && "Invalid value size!");
     assert((Val & ~(~0U >> (32-NumBits))) == 0 && "High bits set!");
     CurValue |= Val << CurBit;
     if (CurBit + NumBits < 32) {
       CurBit += NumBits;
       return;
     }

     // Add the current word.
     WriteWord(CurValue);

     if (CurBit)
       CurValue = Val >> (32-CurBit);
     else
       CurValue = 0;
     CurBit = (CurBit+NumBits) & 31;
   }

   void Emit64(uint64_t Val, unsigned NumBits) {
     if (NumBits <= 32)
       Emit((uint32_t)Val, NumBits);
     else {
       Emit((uint32_t)Val, 32);
       Emit((uint32_t)(Val >> 32), NumBits-32);
     }
   }

   void FlushToWord() {
     if (CurBit) {
       WriteWord(CurValue);
       CurBit = 0;
       CurValue = 0;
     }
   }

   void EmitVBR(uint32_t Val, unsigned NumBits) {
     assert(NumBits <= 32 && "Too many bits to emit!");
     assert(NumBits > 1 && "Too few bits to emit!");
     uint32_t Threshold = 1U << (NumBits-1);

     // Emit the bits with VBR encoding, NumBits-1 bits at a time.
     while (Val >= Threshold) {
       Emit((Val & ((1 << (NumBits-1))-1)) | (1 << (NumBits-1)), NumBits);
       Val >>= NumBits-1;
     }

     Emit(Val, NumBits);
   }

   void EmitVBR64(uint64_t Val, unsigned NumBits) {
     assert(NumBits <= 32 && "Too many bits to emit!");
     assert(NumBits > 1 && "Too few bits to emit!");
     if ((uint32_t)Val == Val)
       return EmitVBR((uint32_t)Val, NumBits);

     uint32_t Threshold = 1U << (NumBits-1);

     // Emit the bits with VBR encoding, NumBits-1 bits at a time.
     while (Val >= Threshold) {
       Emit(((uint32_t)Val & ((1 << (NumBits-1))-1)) |
            (1 << (NumBits-1)), NumBits);
       Val >>= NumBits-1;
     }

     Emit((uint32_t)Val, NumBits);
   }

   /// EmitCode - Emit the specified code.
   void EmitCode(unsigned Val) {
     if (CurCodeSize.IsFixed)
       Emit(Val, CurCodeSize.NumBits);
     else
       EmitVBR(Val, CurCodeSize.NumBits);
   }

   //===--------------------------------------------------------------------===//
   // Block Manipulation
   //===--------------------------------------------------------------------===//

   /// getBlockInfo - If there is block info for the specified ID, return it,
   /// otherwise return null.
   BlockInfo *getBlockInfo(unsigned BlockID) {
     // Common case, the most recent entry matches BlockID.
     if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
       return &BlockInfoRecords.back();

     for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
          i != e; ++i)
       if (BlockInfoRecords[i].BlockID == BlockID)
         return &BlockInfoRecords[i];
     return 0;
   }

 private:
   // Enter block using CodeLen bits to read the size of the code
   // selector associated with the block.
   void EnterSubblock(unsigned BlockID,
                      const NaClBitcodeSelectorAbbrev& CodeLen,
                      BlockInfo *Info) {
     // Block header:
     //    [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
     EmitCode(naclbitc::ENTER_SUBBLOCK);
     EmitVBR(BlockID, naclbitc::BlockIDWidth);
     assert(CodeLen.IsFixed && "Block codelens must be fixed");
     EmitVBR(CodeLen.NumBits, naclbitc::CodeLenWidth);
     FlushToWord();

     unsigned BlockSizeWordIndex = GetWordIndex();
     NaClBitcodeSelectorAbbrev OldCodeSize(CurCodeSize);

     // Emit a placeholder, which will be replaced when the block is popped.
     Emit(0, naclbitc::BlockSizeWidth);

     CurCodeSize = CodeLen;

     // Push the outer block's abbrev set onto the stack, start out with an
     // empty abbrev set.
     BlockScope.push_back(Block(OldCodeSize, BlockSizeWordIndex));
     BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);

     // If there is a blockinfo for this BlockID, add all the predefined abbrevs
     // to the abbrev list.
     if (Info) {
       for (unsigned i = 0, e = static_cast<unsigned>(Info->Abbrevs.size());
            i != e; ++i) {
         CurAbbrevs.push_back(Info->Abbrevs[i]);
         Info->Abbrevs[i]->addRef();
       }
     }
   }

 public:
   /// \brief Enter block using CodeLen bits to read the size of the code
   /// selector associated with the block.
   void EnterSubblock(unsigned BlockID,
                      const NaClBitcodeSelectorAbbrev& CodeLen) {
     EnterSubblock(BlockID, CodeLen, getBlockInfo(BlockID));
   }

   /// \brief Enter block, using a code length based on the number of
   /// (global) BlockInfo entries defined for the block. Note: This
   /// should be used only if the block doesn't define any local abbreviations.
   void EnterSubblock(unsigned BlockID) {
     BlockInfo *Info = getBlockInfo(BlockID);
     size_t NumAbbrevs = Info ? Info->Abbrevs.size() : 0;
     NaClBitcodeSelectorAbbrev DefaultCodeLen(
         naclbitc::DEFAULT_MAX_ABBREV+NumAbbrevs);
     EnterSubblock(BlockID, DefaultCodeLen, Info);
   }

   /// \brief Enter block with the given number of abbreviations.
   void EnterSubblock(unsigned BlockID, unsigned NumAbbrev) {
     NaClBitcodeSelectorAbbrev CodeLenAbbrev(NumAbbrev);
     EnterSubblock(BlockID, CodeLenAbbrev);
   }

   void ExitBlock() {
     assert(!BlockScope.empty() && "Block scope imbalance!");

     // Delete all abbrevs.
     for (unsigned i = 0, e = static_cast<unsigned>(CurAbbrevs.size());
          i != e; ++i)
       CurAbbrevs[i]->dropRef();

     const Block &B = BlockScope.back();

     // Block tail:
     //    [END_BLOCK, <align4bytes>]
     EmitCode(naclbitc::END_BLOCK);
     FlushToWord();

     // Compute the size of the block, in words, not counting the size field.
     unsigned SizeInWords = GetWordIndex() - B.StartSizeWord - 1;
     unsigned ByteNo = B.StartSizeWord*4;

     // Update the block size field in the header of this sub-block.
     BackpatchWord(ByteNo, SizeInWords);

     // Restore the inner block's code size and abbrev table.
     CurCodeSize = B.PrevCodeSize;
     BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
     BlockScope.pop_back();
   }

   //===--------------------------------------------------------------------===//
   // Record Emission
   //===--------------------------------------------------------------------===//

 private:
   /// EmitAbbreviatedField - Emit a single scalar field value with the specified
   /// encoding.
   template<typename uintty>
   void EmitAbbreviatedField(const NaClBitCodeAbbrevOp &Op, uintty V) {
     switch (Op.getEncoding()) {
     case NaClBitCodeAbbrevOp::Literal:
       // This is a no-op, since the abbrev specifies the literal to use.
       assert(V == Op.getValue() && "Invalid abbrev for record!");
       break;
     case NaClBitCodeAbbrevOp::Fixed:
       if (Op.getValue())
         Emit((unsigned)V, (unsigned)Op.getValue());
       break;
     case NaClBitCodeAbbrevOp::VBR:
       if (Op.getValue())
         EmitVBR64(V, (unsigned)Op.getValue());
       break;
     case NaClBitCodeAbbrevOp::Array:
       report_fatal_error("Not to be used with array abbreviation op!");
     case NaClBitCodeAbbrevOp::Char6:
       Emit(NaClBitCodeAbbrevOp::EncodeChar6((char)V), 6);
       break;
     }
   }

   /// EmitRecordWithAbbrevImpl - This is the core implementation of the record
   /// emission code.
   template<typename uintty>
   void EmitRecordWithAbbrevImpl(unsigned Abbrev,
                                 const AbbrevValues<uintty> &Vals) {
     unsigned AbbrevNo = Abbrev-naclbitc::FIRST_APPLICATION_ABBREV;
     assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!");
     NaClBitCodeAbbrev *Abbv = CurAbbrevs[AbbrevNo];

     EmitCode(Abbrev);

     unsigned RecordIdx = 0;
     for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos());
          i != e; ++i) {
       const NaClBitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
       if (Op.getEncoding() == NaClBitCodeAbbrevOp::Array) {
         // Array case.
         assert(i+2 == e && "array op not second to last?");
         const NaClBitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);

         // Emit a vbr6 to indicate the number of elements present.
         EmitVBR(static_cast<uint32_t>(Vals.size()-RecordIdx), 6);

         // Emit each field.
         for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx)
           EmitAbbreviatedField(EltEnc, Vals[RecordIdx]);
       } else {
         assert(RecordIdx < Vals.size() && "Invalid abbrev/record");
         EmitAbbreviatedField(Op, Vals[RecordIdx]);
         ++RecordIdx;
       }
     }
     assert(RecordIdx == Vals.size() && "Not all record operands emitted!");
   }

 public:

   /// Returns true if the given abbreviation index corresponds to a user-defined
   /// abbreviation.
   bool isUserRecordAbbreviation(unsigned Abbrev) const {
     return Abbrev >= naclbitc::FIRST_APPLICATION_ABBREV
         && Abbrev < (CurAbbrevs.size() + naclbitc::FIRST_APPLICATION_ABBREV);
   }

   /// EmitRecord - Emit the specified record to the stream, using an abbrev if
   /// we have one to compress the output.
   template<typename uintty>
   void EmitRecord(unsigned Code, const SmallVectorImpl<uintty> &Vals,
                   unsigned Abbrev = 0) {
     if (!Abbrev) {
       // If we don't have an abbrev to use, emit this in its fully unabbreviated
       // form.
       EmitCode(naclbitc::UNABBREV_RECORD);
       EmitVBR(Code, 6);
       EmitVBR(static_cast<uint32_t>(Vals.size()), 6);
       for (unsigned i = 0, e = static_cast<unsigned>(Vals.size()); i != e; ++i)
         EmitVBR64(Vals[i], 6);
       return;
     }

     // combine code and values, and then emit.
     AbbrevValues<uintty> AbbrevVals(Code, Vals);
     EmitRecordWithAbbrevImpl(Abbrev, AbbrevVals);
   }

   //===--------------------------------------------------------------------===//
   // Abbrev Emission
   //===--------------------------------------------------------------------===//

 private:
   // Emit the abbreviation as a DEFINE_ABBREV record.
   void EncodeAbbrev(NaClBitCodeAbbrev *Abbv) {
     EmitCode(naclbitc::DEFINE_ABBREV);
     EmitVBR(Abbv->getNumOperandInfos(), 5);
     for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos());
          i != e; ++i) {
       const NaClBitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
       bool IsLiteral = Op.isLiteral();
       Emit(IsLiteral, 1);
       if (IsLiteral) {
         EmitVBR64(Op.getValue(), 8);
       } else {
         Emit(Op.getEncoding(), 3);
         if (Op.hasValue())
           EmitVBR64(Op.getValue(), 5);
       }
     }
   }
 public:

   /// EmitAbbrev - This emits an abbreviation to the stream.  Note that this
   /// method takes ownership of the specified abbrev.
   unsigned EmitAbbrev(NaClBitCodeAbbrev *Abbv) {
     assert(Abbv->isValid() && "Can't emit invalid abbreviation!");
     // Emit the abbreviation as a record.
     EncodeAbbrev(Abbv);
     CurAbbrevs.push_back(Abbv);
     return static_cast<unsigned>(CurAbbrevs.size())-1 +
       naclbitc::FIRST_APPLICATION_ABBREV;
   }

   //===--------------------------------------------------------------------===//
   // BlockInfo Block Emission
   //===--------------------------------------------------------------------===//

   /// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK.
   void EnterBlockInfoBlock() {
     EnterSubblock(naclbitc::BLOCKINFO_BLOCK_ID);
     BlockInfoCurBID = ~0U;
   }
 private:
   /// SwitchToBlockID - If we aren't already talking about the specified block
   /// ID, emit a BLOCKINFO_CODE_SETBID record.
   void SwitchToBlockID(unsigned BlockID) {
     if (BlockInfoCurBID == BlockID) return;
     SmallVector<unsigned, 2> V;
     V.push_back(BlockID);
     EmitRecord(naclbitc::BLOCKINFO_CODE_SETBID, V);
     BlockInfoCurBID = BlockID;
   }

   BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
     if (BlockInfo *BI = getBlockInfo(BlockID))
       return *BI;

     // Otherwise, add a new record.
     BlockInfoRecords.push_back(BlockInfo());
     BlockInfoRecords.back().BlockID = BlockID;
     return BlockInfoRecords.back();
   }

 public:

   /// EmitBlockInfoAbbrev - Emit a DEFINE_ABBREV record for the specified
   /// BlockID.
   unsigned EmitBlockInfoAbbrev(unsigned BlockID, NaClBitCodeAbbrev *Abbv) {
     SwitchToBlockID(BlockID);
     EncodeAbbrev(Abbv);

     // Add the abbrev to the specified block record.
     BlockInfo &Info = getOrCreateBlockInfo(BlockID);
     Info.Abbrevs.push_back(Abbv);

     return Info.Abbrevs.size()-1+naclbitc::FIRST_APPLICATION_ABBREV;
   }
 };


 } // End llvm namespace

 #endif
	//===- NaClBitstreamWriter.h - NaCl bitstream writer ------------- C++ --===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This header defines the BitstreamWriter class. This class can be used to
	// write an arbitrary bitstream, regardless of its contents.
	//
	//===----------------------------------------------------------------------===//

	#ifndef LLVM_BITCODE_NACL_NACLBITSTREAMWRITER_H
	#define LLVM_BITCODE_NACL_NACLBITSTREAMWRITER_H

	#include "llvm/ADT/SmallVector.h"
	#include "llvm/ADT/StringRef.h"
	#include "llvm/Bitcode/NaCl/NaClBitCodes.h"
	#include <vector>

	namespace llvm {

	class NaClBitstreamWriter {
	SmallVectorImpl<char> &Out;

	/// CurBit - Always between 0 and 31 inclusive, specifies the next bit to use.
	unsigned CurBit;

	/// CurValue - The current value. Only bits < CurBit are valid.
	uint32_t CurValue;

	/// CurCodeSize - This is the declared size of code values used for the
	/// current block, in bits.
	NaClBitcodeSelectorAbbrev CurCodeSize;

	/// BlockInfoCurBID - When emitting a BLOCKINFO_BLOCK, this is the currently
	/// selected BLOCK ID.
	unsigned BlockInfoCurBID;

	/// CurAbbrevs - Abbrevs installed at in this block.
	std::vector<NaClBitCodeAbbrev*> CurAbbrevs;

	struct Block {
	NaClBitcodeSelectorAbbrev PrevCodeSize;
	unsigned StartSizeWord;
	std::vector<NaClBitCodeAbbrev*> PrevAbbrevs;
	Block(const NaClBitcodeSelectorAbbrev& PCS, unsigned SSW)
	: PrevCodeSize(PCS), StartSizeWord(SSW) {}
	};

	/// BlockScope - This tracks the current blocks that we have entered.
	std::vector<Block> BlockScope;

	/// BlockInfo - This contains information emitted to BLOCKINFO_BLOCK blocks.
	/// These describe abbreviations that all blocks of the specified ID inherit.
	struct BlockInfo {
	unsigned BlockID;
	std::vector<NaClBitCodeAbbrev*> Abbrevs;
	};
	std::vector<BlockInfo> BlockInfoRecords;

	/// AbbrevValues - Wrapper class that allows the bitstream writer to
	/// prefix a code to the set of values, associated with a record to
	/// emit, without having to destructively change the contents of
	/// values.
	template<typename uintty>
	struct AbbrevValues {
	AbbrevValues(uintty Code, const SmallVectorImpl<uintty> &Values)
	: Code(Code), Values(Values) {}

	size_t size() const {
	return Values.size() + 1;
	}

	uintty operator[](size_t Index) const {
	return Index == 0 ? Code : Values[Index-1];
	}

	private:
	// The code to use (if not DONT_USE_CODE).
	uintty Code;
	const SmallVectorImpl<uintty> &Values;
	};

	public:
	// BackpatchWord - Backpatch a 32-bit word in the output with the specified
	// value.
	void BackpatchWord(unsigned ByteNo, unsigned NewWord) {
	Out[ByteNo++] = (unsigned char)(NewWord >> 0);
	Out[ByteNo++] = (unsigned char)(NewWord >> 8);
	Out[ByteNo++] = (unsigned char)(NewWord >> 16);
	Out[ByteNo ] = (unsigned char)(NewWord >> 24);
	}

	private:
	void WriteByte(unsigned char Value) {
	Out.push_back(Value);
	}

	void WriteWord(unsigned Value) {
	unsigned char Bytes[4] = {
	(unsigned char)(Value >> 0),
	(unsigned char)(Value >> 8),
	(unsigned char)(Value >> 16),
	(unsigned char)(Value >> 24) };
	Out.append(&Bytes[0], &Bytes[4]);
	}

	unsigned GetBufferOffset() const {
	return Out.size();
	}

	unsigned GetWordIndex() const {
	unsigned Offset = GetBufferOffset();
	assert((Offset & 3) == 0 && "Not 32-bit aligned");
	return Offset / 4;
	}

	public:
	explicit NaClBitstreamWriter(SmallVectorImpl<char> &O)
	: Out(O), CurBit(0), CurValue(0), CurCodeSize() {}

	~NaClBitstreamWriter() {
	assert(CurBit == 0 && "Unflused data remaining");
	assert(BlockScope.empty() && CurAbbrevs.empty() && "Block imbalance");

	// Free the BlockInfoRecords.
	while (!BlockInfoRecords.empty()) {
	BlockInfo &Info = BlockInfoRecords.back();
	// Free blockinfo abbrev info.
	for (unsigned i = 0, e = static_cast<unsigned>(Info.Abbrevs.size());
	i != e; ++i)
	Info.Abbrevs[i]->dropRef();
	BlockInfoRecords.pop_back();
	}
	}

	/// \brief Retrieve the current position in the stream, in bits.
	uint64_t GetCurrentBitNo() const { return GetBufferOffset() * 8 + CurBit; }

	//===--------------------------------------------------------------------===//
	// Basic Primitives for emitting bits to the stream.
	//===--------------------------------------------------------------------===//

	void Emit(uint32_t Val, unsigned NumBits) {
	assert(NumBits && NumBits <= 32 && "Invalid value size!");
	assert((Val & ~(~0U >> (32-NumBits))) == 0 && "High bits set!");
	CurValue \|= Val << CurBit;
	if (CurBit + NumBits < 32) {
	CurBit += NumBits;
	return;
	}

	// Add the current word.
	WriteWord(CurValue);

	if (CurBit)
	CurValue = Val >> (32-CurBit);
	else
	CurValue = 0;
	CurBit = (CurBit+NumBits) & 31;
	}

	void Emit64(uint64_t Val, unsigned NumBits) {
	if (NumBits <= 32)
	Emit((uint32_t)Val, NumBits);
	else {
	Emit((uint32_t)Val, 32);
	Emit((uint32_t)(Val >> 32), NumBits-32);
	}
	}

	void FlushToWord() {
	if (CurBit) {
	WriteWord(CurValue);
	CurBit = 0;
	CurValue = 0;
	}
	}

	void EmitVBR(uint32_t Val, unsigned NumBits) {
	assert(NumBits <= 32 && "Too many bits to emit!");
	assert(NumBits > 1 && "Too few bits to emit!");
	uint32_t Threshold = 1U << (NumBits-1);

	// Emit the bits with VBR encoding, NumBits-1 bits at a time.
	while (Val >= Threshold) {
	Emit((Val & ((1 << (NumBits-1))-1)) \| (1 << (NumBits-1)), NumBits);
	Val >>= NumBits-1;
	}

	Emit(Val, NumBits);
	}

	void EmitVBR64(uint64_t Val, unsigned NumBits) {
	assert(NumBits <= 32 && "Too many bits to emit!");
	assert(NumBits > 1 && "Too few bits to emit!");
	if ((uint32_t)Val == Val)
	return EmitVBR((uint32_t)Val, NumBits);

	uint32_t Threshold = 1U << (NumBits-1);

	// Emit the bits with VBR encoding, NumBits-1 bits at a time.
	while (Val >= Threshold) {
	Emit(((uint32_t)Val & ((1 << (NumBits-1))-1)) \|
	(1 << (NumBits-1)), NumBits);
	Val >>= NumBits-1;
	}

	Emit((uint32_t)Val, NumBits);
	}

	/// EmitCode - Emit the specified code.
	void EmitCode(unsigned Val) {
	if (CurCodeSize.IsFixed)
	Emit(Val, CurCodeSize.NumBits);
	else
	EmitVBR(Val, CurCodeSize.NumBits);
	}

	//===--------------------------------------------------------------------===//
	// Block Manipulation
	//===--------------------------------------------------------------------===//

	/// getBlockInfo - If there is block info for the specified ID, return it,
	/// otherwise return null.
	BlockInfo *getBlockInfo(unsigned BlockID) {
	// Common case, the most recent entry matches BlockID.
	if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
	return &BlockInfoRecords.back();

	for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
	i != e; ++i)
	if (BlockInfoRecords[i].BlockID == BlockID)
	return &BlockInfoRecords[i];
	return 0;
	}

	private:
	// Enter block using CodeLen bits to read the size of the code
	// selector associated with the block.
	void EnterSubblock(unsigned BlockID,
	const NaClBitcodeSelectorAbbrev& CodeLen,
	BlockInfo *Info) {
	// Block header:
	// [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
	EmitCode(naclbitc::ENTER_SUBBLOCK);
	EmitVBR(BlockID, naclbitc::BlockIDWidth);
	assert(CodeLen.IsFixed && "Block codelens must be fixed");
	EmitVBR(CodeLen.NumBits, naclbitc::CodeLenWidth);
	FlushToWord();

	unsigned BlockSizeWordIndex = GetWordIndex();
	NaClBitcodeSelectorAbbrev OldCodeSize(CurCodeSize);

	// Emit a placeholder, which will be replaced when the block is popped.
	Emit(0, naclbitc::BlockSizeWidth);

	CurCodeSize = CodeLen;

	// Push the outer block's abbrev set onto the stack, start out with an
	// empty abbrev set.
	BlockScope.push_back(Block(OldCodeSize, BlockSizeWordIndex));
	BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);

	// If there is a blockinfo for this BlockID, add all the predefined abbrevs
	// to the abbrev list.
	if (Info) {
	for (unsigned i = 0, e = static_cast<unsigned>(Info->Abbrevs.size());
	i != e; ++i) {
	CurAbbrevs.push_back(Info->Abbrevs[i]);
	Info->Abbrevs[i]->addRef();
	}
	}
	}

	public:
	/// \brief Enter block using CodeLen bits to read the size of the code
	/// selector associated with the block.
	void EnterSubblock(unsigned BlockID,
	const NaClBitcodeSelectorAbbrev& CodeLen) {
	EnterSubblock(BlockID, CodeLen, getBlockInfo(BlockID));
	}

	/// \brief Enter block, using a code length based on the number of
	/// (global) BlockInfo entries defined for the block. Note: This
	/// should be used only if the block doesn't define any local abbreviations.
	void EnterSubblock(unsigned BlockID) {
	BlockInfo *Info = getBlockInfo(BlockID);
	size_t NumAbbrevs = Info ? Info->Abbrevs.size() : 0;
	NaClBitcodeSelectorAbbrev DefaultCodeLen(
	naclbitc::DEFAULT_MAX_ABBREV+NumAbbrevs);
	EnterSubblock(BlockID, DefaultCodeLen, Info);
	}

	/// \brief Enter block with the given number of abbreviations.
	void EnterSubblock(unsigned BlockID, unsigned NumAbbrev) {
	NaClBitcodeSelectorAbbrev CodeLenAbbrev(NumAbbrev);
	EnterSubblock(BlockID, CodeLenAbbrev);
	}

	void ExitBlock() {
	assert(!BlockScope.empty() && "Block scope imbalance!");

	// Delete all abbrevs.
	for (unsigned i = 0, e = static_cast<unsigned>(CurAbbrevs.size());
	i != e; ++i)
	CurAbbrevs[i]->dropRef();

	const Block &B = BlockScope.back();

	// Block tail:
	// [END_BLOCK, <align4bytes>]
	EmitCode(naclbitc::END_BLOCK);
	FlushToWord();

	// Compute the size of the block, in words, not counting the size field.
	unsigned SizeInWords = GetWordIndex() - B.StartSizeWord - 1;
	unsigned ByteNo = B.StartSizeWord*4;

	// Update the block size field in the header of this sub-block.
	BackpatchWord(ByteNo, SizeInWords);

	// Restore the inner block's code size and abbrev table.
	CurCodeSize = B.PrevCodeSize;
	BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
	BlockScope.pop_back();
	}

	//===--------------------------------------------------------------------===//
	// Record Emission
	//===--------------------------------------------------------------------===//

	private:
	/// EmitAbbreviatedField - Emit a single scalar field value with the specified
	/// encoding.
	template<typename uintty>
	void EmitAbbreviatedField(const NaClBitCodeAbbrevOp &Op, uintty V) {
	switch (Op.getEncoding()) {
	case NaClBitCodeAbbrevOp::Literal:
	// This is a no-op, since the abbrev specifies the literal to use.
	assert(V == Op.getValue() && "Invalid abbrev for record!");
	break;
	case NaClBitCodeAbbrevOp::Fixed:
	if (Op.getValue())
	Emit((unsigned)V, (unsigned)Op.getValue());
	break;
	case NaClBitCodeAbbrevOp::VBR:
	if (Op.getValue())
	EmitVBR64(V, (unsigned)Op.getValue());
	break;
	case NaClBitCodeAbbrevOp::Array:
	report_fatal_error("Not to be used with array abbreviation op!");
	case NaClBitCodeAbbrevOp::Char6:
	Emit(NaClBitCodeAbbrevOp::EncodeChar6((char)V), 6);
	break;
	}
	}

	/// EmitRecordWithAbbrevImpl - This is the core implementation of the record
	/// emission code.
	template<typename uintty>
	void EmitRecordWithAbbrevImpl(unsigned Abbrev,
	const AbbrevValues<uintty> &Vals) {
	unsigned AbbrevNo = Abbrev-naclbitc::FIRST_APPLICATION_ABBREV;
	assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!");
	NaClBitCodeAbbrev *Abbv = CurAbbrevs[AbbrevNo];

	EmitCode(Abbrev);

	unsigned RecordIdx = 0;
	for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos());
	i != e; ++i) {
	const NaClBitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
	if (Op.getEncoding() == NaClBitCodeAbbrevOp::Array) {
	// Array case.
	assert(i+2 == e && "array op not second to last?");
	const NaClBitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);

	// Emit a vbr6 to indicate the number of elements present.
	EmitVBR(static_cast<uint32_t>(Vals.size()-RecordIdx), 6);

	// Emit each field.
	for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx)
	EmitAbbreviatedField(EltEnc, Vals[RecordIdx]);
	} else {
	assert(RecordIdx < Vals.size() && "Invalid abbrev/record");
	EmitAbbreviatedField(Op, Vals[RecordIdx]);
	++RecordIdx;
	}
	}
	assert(RecordIdx == Vals.size() && "Not all record operands emitted!");
	}

	public:

	/// Returns true if the given abbreviation index corresponds to a user-defined
	/// abbreviation.
	bool isUserRecordAbbreviation(unsigned Abbrev) const {
	return Abbrev >= naclbitc::FIRST_APPLICATION_ABBREV
	&& Abbrev < (CurAbbrevs.size() + naclbitc::FIRST_APPLICATION_ABBREV);
	}

	/// EmitRecord - Emit the specified record to the stream, using an abbrev if
	/// we have one to compress the output.
	template<typename uintty>
	void EmitRecord(unsigned Code, const SmallVectorImpl<uintty> &Vals,
	unsigned Abbrev = 0) {
	if (!Abbrev) {
	// If we don't have an abbrev to use, emit this in its fully unabbreviated
	// form.
	EmitCode(naclbitc::UNABBREV_RECORD);
	EmitVBR(Code, 6);
	EmitVBR(static_cast<uint32_t>(Vals.size()), 6);
	for (unsigned i = 0, e = static_cast<unsigned>(Vals.size()); i != e; ++i)
	EmitVBR64(Vals[i], 6);
	return;
	}

	// combine code and values, and then emit.
	AbbrevValues<uintty> AbbrevVals(Code, Vals);
	EmitRecordWithAbbrevImpl(Abbrev, AbbrevVals);
	}

	//===--------------------------------------------------------------------===//
	// Abbrev Emission
	//===--------------------------------------------------------------------===//

	private:
	// Emit the abbreviation as a DEFINE_ABBREV record.
	void EncodeAbbrev(NaClBitCodeAbbrev *Abbv) {
	EmitCode(naclbitc::DEFINE_ABBREV);
	EmitVBR(Abbv->getNumOperandInfos(), 5);
	for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos());
	i != e; ++i) {
	const NaClBitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
	bool IsLiteral = Op.isLiteral();
	Emit(IsLiteral, 1);
	if (IsLiteral) {
	EmitVBR64(Op.getValue(), 8);
	} else {
	Emit(Op.getEncoding(), 3);
	if (Op.hasValue())
	EmitVBR64(Op.getValue(), 5);
	}
	}
	}
	public:

	/// EmitAbbrev - This emits an abbreviation to the stream. Note that this
	/// method takes ownership of the specified abbrev.
	unsigned EmitAbbrev(NaClBitCodeAbbrev *Abbv) {
	assert(Abbv->isValid() && "Can't emit invalid abbreviation!");
	// Emit the abbreviation as a record.
	EncodeAbbrev(Abbv);
	CurAbbrevs.push_back(Abbv);
	return static_cast<unsigned>(CurAbbrevs.size())-1 +
	naclbitc::FIRST_APPLICATION_ABBREV;
	}

	//===--------------------------------------------------------------------===//
	// BlockInfo Block Emission
	//===--------------------------------------------------------------------===//

	/// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK.
	void EnterBlockInfoBlock() {
	EnterSubblock(naclbitc::BLOCKINFO_BLOCK_ID);
	BlockInfoCurBID = ~0U;
	}
	private:
	/// SwitchToBlockID - If we aren't already talking about the specified block
	/// ID, emit a BLOCKINFO_CODE_SETBID record.
	void SwitchToBlockID(unsigned BlockID) {
	if (BlockInfoCurBID == BlockID) return;
	SmallVector<unsigned, 2> V;
	V.push_back(BlockID);
	EmitRecord(naclbitc::BLOCKINFO_CODE_SETBID, V);
	BlockInfoCurBID = BlockID;
	}

	BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
	if (BlockInfo *BI = getBlockInfo(BlockID))
	return *BI;

	// Otherwise, add a new record.
	BlockInfoRecords.push_back(BlockInfo());
	BlockInfoRecords.back().BlockID = BlockID;
	return BlockInfoRecords.back();
	}

	public:

	/// EmitBlockInfoAbbrev - Emit a DEFINE_ABBREV record for the specified
	/// BlockID.
	unsigned EmitBlockInfoAbbrev(unsigned BlockID, NaClBitCodeAbbrev *Abbv) {
	SwitchToBlockID(BlockID);
	EncodeAbbrev(Abbv);

	// Add the abbrev to the specified block record.
	BlockInfo &Info = getOrCreateBlockInfo(BlockID);
	Info.Abbrevs.push_back(Abbv);

	return Info.Abbrevs.size()-1+naclbitc::FIRST_APPLICATION_ABBREV;
	}
	};


	} // End llvm namespace

	#endif