xref: /third_party/lzma/C/Bra.h

/* Bra.h -- Branch converters for executables
2023-04-02 : Igor Pavlov : Public domain */

#ifndef ZIP7_INC_BRA_H
#define ZIP7_INC_BRA_H

#include "7zTypes.h"

EXTERN_C_BEGIN

#define Z7_BRANCH_CONV_DEC(name)    z7_BranchConv_   ## name ## _Dec
#define Z7_BRANCH_CONV_ENC(name)    z7_BranchConv_   ## name ## _Enc
#define Z7_BRANCH_CONV_ST_DEC(name) z7_BranchConvSt_ ## name ## _Dec
#define Z7_BRANCH_CONV_ST_ENC(name) z7_BranchConvSt_ ## name ## _Enc

#define Z7_BRANCH_CONV_DECL(name)    Byte * name(Byte *data, SizeT size, UInt32 pc)
#define Z7_BRANCH_CONV_ST_DECL(name) Byte * name(Byte *data, SizeT size, UInt32 pc, UInt32 *state)

typedef Z7_BRANCH_CONV_DECL(   (*z7_Func_BranchConv));
typedef Z7_BRANCH_CONV_ST_DECL((*z7_Func_BranchConvSt));

#define Z7_BRANCH_CONV_ST_X86_STATE_INIT_VAL 0
Z7_BRANCH_CONV_ST_DECL(Z7_BRANCH_CONV_ST_DEC(X86));
Z7_BRANCH_CONV_ST_DECL(Z7_BRANCH_CONV_ST_ENC(X86));

#define Z7_BRANCH_FUNCS_DECL(name) \
Z7_BRANCH_CONV_DECL(Z7_BRANCH_CONV_DEC(name)); \
Z7_BRANCH_CONV_DECL(Z7_BRANCH_CONV_ENC(name));

Z7_BRANCH_FUNCS_DECL(ARM64)
Z7_BRANCH_FUNCS_DECL(ARM)
Z7_BRANCH_FUNCS_DECL(ARMT)
Z7_BRANCH_FUNCS_DECL(PPC)
Z7_BRANCH_FUNCS_DECL(SPARC)
Z7_BRANCH_FUNCS_DECL(IA64)

/*
These functions convert data that contain CPU instructions.
Each such function converts relative addresses to absolute addresses in some
branch instructions: CALL (in all converters) and JUMP (X86 converter only).
Such conversion allows to increase compression ratio, if we compress that data.

There are 2 types of converters:
  Byte * Conv_RISC (Byte *data, SizeT size, UInt32 pc);
  Byte * ConvSt_X86(Byte *data, SizeT size, UInt32 pc, UInt32 *state);
Each Converter supports 2 versions: one for encoding
and one for decoding (_Enc/_Dec postfixes in function name).

In params:
  data  : data buffer
  size  : size of data
  pc    : current virtual Program Counter (Instruction Pinter) value
In/Out param:
  state : pointer to state variable (for X86 converter only)

Return:
  The pointer to position in (data) buffer after last byte that was processed.
  If the caller calls converter again, it must call it starting with that position.
  But the caller is allowed to move data in buffer. so pointer to
  current processed position also will be changed for next call.
  Also the caller must increase internal (pc) value for next call.

Each converter has some characteristics: Endian, Alignment, LookAhead.
  Type   Endian  Alignment  LookAhead

  X86    little      1          4
  ARMT   little      2          2
  ARM    little      4          0
  ARM64  little      4          0
  PPC     big        4          0
  SPARC   big        4          0
  IA64   little     16          0

  (data) must be aligned for (Alignment).
  processed size can be calculated as:
    SizeT processed = Conv(data, size, pc) - data;
  if (processed == 0)
    it means that converter needs more data for processing.
  If (size < Alignment + LookAhead)
    then (processed == 0) is allowed.

Example code for conversion in loop:
  UInt32 pc = 0;
  size = 0;
  for (;;)
  {
    size += Load_more_input_data(data + size);
    SizeT processed = Conv(data, size, pc) - data;
    if (processed == 0 && no_more_input_data_after_size)
      break; // we stop convert loop
    data += processed;
    size -= processed;
    pc += processed;
  }
*/

EXTERN_C_END

#endif