Jump size optimization...

// Author: Orlando Llanes
//
// This code is hereby donated to the public domain
//
// asm.cpp : Defines the entry point for the console application.
//
 
#include "stdafx.h"
 
#include <ctype.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
 
  typedef struct
  {
    int Source;
    int Target;
    int ActualSize;
    int Size;
  } TBranchOp;
 
int main(int argc, char* argv[])
{
  char            Src[] = "j4 :2 n n j5 :3 n j2 :4 j3 :5 r";
  int             SrcPos = 0;
 
  unsigned __int8 Code[1024];
  int             CodeOfs = 0;
 
  int             Target[10];
 
  TBranchOp       Branch[1024];
  int             nBranch = 0;
 
  int             Tmp;
  int             i;
  int             j;
  int             k;
  int             l;
 
  int             SizeDiff;
 
  char            Ch;
 
  FILE*           Out;
 
  memset( Code, 0, sizeof Code );
  memset( Target, 0xFF, sizeof Target );
  memset( Branch, 0, sizeof Branch );
 
  while( Src[SrcPos] )
  {
    do
    {
      Ch = Src[SrcPos++];
    } while( isspace(Ch) );
 
    switch( Ch )
    {
      case 'j':
        Ch = Src[SrcPos++];
        printf( " jmp %c\n", Ch );
 
        Branch[nBranch].Source     = CodeOfs;
        Branch[nBranch].Target     = Ch;
        Branch[nBranch].ActualSize = 2;
        Branch[nBranch].Size       = 2;
        nBranch++;
 
        Code[CodeOfs++] = 0xEB;
        Code[CodeOfs++] = 0;
        break;
 
      case ':':
        Ch = Src[SrcPos++];
        printf( "%c:\n", Ch );
        if( Target[Ch - '0'] != -1 )
        {
          printf( "Error: Label %c has already been declared\n", Ch );
          return 0;
        }
        Target[Ch - '0'] = CodeOfs;
        break;
 
      case 'n':
        printf( " nop\n" );
        Code[CodeOfs++] = 0x90;
        break;
 
      case 'r':
        printf( " ret\n" );
        Code[CodeOfs++] = 0xC3;
        break;
    }
  }
 
  // Grow jump targets in place
  do
  {
    SizeDiff = 0;
 
    for( i = 0; i < nBranch; i++ )
    {
      j = Branch[i].Source;
      k = Branch[i].Target;
      l = Target[k - '0'];
 
      if( l == -1 )
      {
        printf( "Error: Label '%c' undeclared.\n", k );
        return 0;
      }
 
      Tmp = l - j - Branch[i].Size;
 
      if( (abs(Tmp) > 128) && (Branch[i].Size <= 2) )
      {
        for( k = 0; k < 10; k++ )
        {
          if( Target[k] > Branch[i].Source )
          {
            if( Target[k] )
              Target[k]++;
          }
        }
 
        for( k = 0; k < nBranch; k++ )
        {
          if( Branch[k].Source > Branch[i].Source )
            Branch[k].Source++;
        }
 
        memmove( &Code[j + 3], &Code[j + 2], CodeOfs - j - 1 );
        CodeOfs++;
 
        Code[j] = 0xE9;
        SizeDiff++;
        Branch[i].Size++;
      }
    }
  } while( SizeDiff );
 
  // Fill in jump targets
  for( i = 0; i < nBranch; i++ )
  {
    j = Branch[i].Source;
    k = Branch[i].Target;
    l = Target[k - '0'];
 
    Tmp = l - j - Branch[i].Size;
 
    Code[j + 1] = Tmp;
    if( Branch[i].Size >= 3 )
      Code[j + 2] = Tmp >> 8;
  }
 
  Out = fopen("a.com", "w+b");
  if( Out )
  {
    fwrite( Code, 1, CodeOfs, Out );
 
    fclose( Out );
  }
 
  for( i = 0; i < CodeOfs; i++ )
    printf( "0x%.2X\n", Code[i] );
 
  return 0;
}