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//
// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.
//
#ifndef _GCREFMAP_H_
#define _GCREFMAP_H_
#include "sigbuilder.h"
//
// The GCRef map is used to encode GC type of arguments for callsites. Logically, it is sequence <pos, token> where pos is
// position of the reference in the stack frame and token is type of GC reference (one of GCREFMAP_XXX values).
//
// - The encoding always starts at the byte boundary. The high order bit of each byte is used to signal end of the encoding
// stream. The last byte has the high order bit zero. It means that there are 7 useful bits in each byte.
// - "pos" is always encoded as delta from previous pos.
// - The basic encoding unit is two bits. Values 0, 1 and 2 are the common constructs (skip single slot, GC reference, interior
// pointer). Value 3 means that extended encoding follows.
// - The extended information is integer encoded in one or more four bit blocks. The high order bit of the four bit block is
// used to signal the end.
// - For x86, the encoding starts by size of the callee poped stack. The size is encoded using the same mechanism as above (two bit
// basic encoding, with extended encoding for large values).
/////////////////////////////////////////////////////////////////////////////////////
// A utility class to encode sequence of GC summaries for a callsite
class GCRefMapBuilder
{
int m_PendingByte; // Pending value, not yet written out
int m_Bits; // Number of bits in pending byte. Note that the trailing zero bits are not written out,
// so this can be more than 7.
int m_Pos; // Current position
SigBuilder m_SigBuilder;
// Append single bit to the stream
void AppendBit(int bit)
{
if (bit != 0)
{
while (m_Bits >= 7)
{
m_SigBuilder.AppendByte((BYTE)(m_PendingByte | 0x80));
m_PendingByte = 0;
m_Bits -= 7;
}
m_PendingByte |= (1 << m_Bits);
}
m_Bits++;
}
void AppendTwoBit(int bits)
{
AppendBit(bits & 1);
AppendBit(bits >> 1);
}
void AppendInt(int val)
{
do {
AppendBit(val & 1);
AppendBit((val >> 1) & 1);
AppendBit((val >> 2) & 1);
val >>= 3;
AppendBit((val != 0) ? 1 : 0);
}
while (val != 0);
}
public:
GCRefMapBuilder()
: m_PendingByte(0), m_Bits(0), m_Pos(0)
{
}
#ifdef _TARGET_X86_
void WriteStackPop(int stackPop)
{
if (stackPop < 3)
{
AppendTwoBit(stackPop);
}
else
{
AppendTwoBit(3);
AppendInt(stackPop - 3);
}
}
#endif
void WriteToken(int pos, int gcRefMapToken)
{
int posDelta = pos - m_Pos;
m_Pos = pos + 1;
if (posDelta != 0)
{
if (posDelta < 4)
{
// Skipping by one slot at a time for small deltas produces smaller encoding.
while (posDelta > 0)
{
AppendTwoBit(0);
posDelta--;
}
}
else
{
AppendTwoBit(3);
AppendInt((posDelta - 4) << 1);
}
}
if (gcRefMapToken < 3)
{
AppendTwoBit(gcRefMapToken);
}
else
{
AppendTwoBit(3);
AppendInt(((gcRefMapToken - 3) << 1) | 1);
}
}
void Flush()
{
if ((m_PendingByte & 0x7F) != 0 || m_Pos == 0)
m_SigBuilder.AppendByte((BYTE)(m_PendingByte & 0x7F));
m_PendingByte = 0;
m_Bits = 0;
m_Pos = 0;
}
PVOID GetBlob(DWORD * pdwLength)
{
return m_SigBuilder.GetSignature(pdwLength);
}
DWORD GetBlobLength()
{
return m_SigBuilder.GetSignatureLength();
}
};
/////////////////////////////////////////////////////////////////////////////////////
// A utility class to decode a GC summary for a callsite
class GCRefMapDecoder
{
PTR_BYTE m_pCurrentByte;
int m_PendingByte;
int m_Pos;
FORCEINLINE int GetBit()
{
int x = m_PendingByte;
if (x & 0x80)
{
x = *m_pCurrentByte++;
x |= ((x & 0x80) << 7);
}
m_PendingByte = x >> 1;
return x & 1;
}
FORCEINLINE int GetTwoBit()
{
int result = GetBit();
result |= GetBit() << 1;
return result;
}
int GetInt()
{
int result = 0;
int bit = 0;
do {
result |= GetBit() << (bit++);
result |= GetBit() << (bit++);
result |= GetBit() << (bit++);
}
while (GetBit() != 0);
return result;
}
public:
GCRefMapDecoder(PTR_BYTE pBlob)
: m_pCurrentByte(pBlob), m_PendingByte(0x80), m_Pos(0)
{
}
BOOL AtEnd()
{
return m_PendingByte == 0;
}
#ifdef _TARGET_X86_
UINT ReadStackPop()
{
int x = GetTwoBit();
if (x == 3)
x = GetInt() + 3;
return x;
}
#endif
int CurrentPos()
{
return m_Pos;
}
int ReadToken()
{
int val = GetTwoBit();
if (val == 3)
{
int ext = GetInt();
if ((ext & 1) == 0)
{
m_Pos += (ext >> 1) + 4;
return GCREFMAP_SKIP;
}
else
{
m_Pos++;
return (ext >> 1) + 3;
}
}
m_Pos++;
return val;
}
};
#endif // _GCREFMAP_H_
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