sdd1emu.c

linux下的任天堂模拟器代码。供大家参考。

/*
Copyright (C) 1997-2007 ZSNES Team ( zsKnight, _Demo_, pagefault, Nach )

http://www.zsnes.com
http://sourceforge.net/projects/zsnes
https://zsnes.bountysource.com

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
version 2 as published by the Free Software Foundation.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/


/*******************************************************************************
  S-DD1 C emulator code
  (c) Copyright 2003 Brad Jorsch with research by
                     Andreas Naive and John Weidman
*******************************************************************************/
/* S-DD1 decompressor
 *
 * Based on code and documentation by Andreas Naive, who deserves a great deal
 * of thanks and credit for figuring this out.
 *
 * Andreas says:
 * The author is greatly indebted with The Dumper, without whose help and
 * patience providing him with real S-DD1 data the research had never been
 * possible. He also wish to note that in the very beggining of his research,
 * Neviksti had done some steps in the right direction. By last, the author is
 * indirectly indebted to all the people that worked and contributed in the
 * S-DD1 issue in the past.
 */

#include <string.h>

#ifndef __GNUC__
#define INLINE
#else
#define INLINE static inline
#endif

static int valid_bits;
static unsigned short in_stream;
static unsigned char *in_buf;
static unsigned char bit_ctr[8];
static unsigned char context_states[32];
static int context_MPS[32];
static int bitplane_type;
static int high_context_bits;
static int low_context_bits;
static int prev_bits[8];

static struct {
    unsigned char code_size;
    unsigned char MPS_next;
    unsigned char LPS_next;
} evolution_table[] = {
    /*  0 */ { 0,25,25},
    /*  1 */ { 0, 2, 1},
    /*  2 */ { 0, 3, 1},
    /*  3 */ { 0, 4, 2},
    /*  4 */ { 0, 5, 3},
    /*  5 */ { 1, 6, 4},
    /*  6 */ { 1, 7, 5},
    /*  7 */ { 1, 8, 6},
    /*  8 */ { 1, 9, 7},
    /*  9 */ { 2,10, 8},
    /* 10 */ { 2,11, 9},
    /* 11 */ { 2,12,10},
    /* 12 */ { 2,13,11},
    /* 13 */ { 3,14,12},
    /* 14 */ { 3,15,13},
    /* 15 */ { 3,16,14},
    /* 16 */ { 3,17,15},
    /* 17 */ { 4,18,16},
    /* 18 */ { 4,19,17},
    /* 19 */ { 5,20,18},
    /* 20 */ { 5,21,19},
    /* 21 */ { 6,22,20},
    /* 22 */ { 6,23,21},
    /* 23 */ { 7,24,22},
    /* 24 */ { 7,24,23},
    /* 25 */ { 0,26, 1},
    /* 26 */ { 1,27, 2},
    /* 27 */ { 2,28, 4},
    /* 28 */ { 3,29, 8},
    /* 29 */ { 4,30,12},
    /* 30 */ { 5,31,16},
    /* 31 */ { 6,32,18},
    /* 32 */ { 7,24,22}
};

static unsigned char run_table[128] = {
    128,  64,  96,  32, 112,  48,  80,  16, 120,  56,  88,  24, 104,  40,  72,
      8, 124,  60,  92,  28, 108,  44,  76,  12, 116,  52,  84,  20, 100,  36,
     68,   4, 126,  62,  94,  30, 110,  46,  78,  14, 118,  54,  86,  22, 102,
     38,  70,   6, 122,  58,  90,  26, 106,  42,  74,  10, 114,  50,  82,  18,
     98,  34,  66,   2, 127,  63,  95,  31, 111,  47,  79,  15, 119,  55,  87,
     23, 103,  39,  71,   7, 123,  59,  91,  27, 107,  43,  75,  11, 115,  51,
     83,  19,  99,  35,  67,   3, 125,  61,  93,  29, 109,  45,  77,  13, 117,
     53,  85,  21, 101,  37,  69,   5, 121,  57,  89,  25, 105,  41,  73,   9,
    113,  49,  81,  17,  97,  33,  65,   1
};

INLINE unsigned char GetCodeword(int bits){
    unsigned char tmp;

    if(!valid_bits){
        in_stream|=*(in_buf++);
        valid_bits=8;
    }
    in_stream<<=1;
    valid_bits--;
    in_stream^=0x8000;
    if(in_stream&0x8000) return 0x80+(1<<bits);
    tmp=(in_stream>>8) | (0x7f>>bits);
    in_stream<<=bits;
    valid_bits-=bits;
    if(valid_bits<0){
        in_stream |= (*(in_buf++))<<(-valid_bits);
        valid_bits+=8;
    }
    return run_table[tmp];
}

INLINE unsigned char GolombGetBit(int code_size){
    if(!bit_ctr[code_size]) bit_ctr[code_size]=GetCodeword(code_size);
    bit_ctr[code_size]--;
    if(bit_ctr[code_size]==0x80){
        bit_ctr[code_size]=0;
        return 2; /* secret code for 'last zero'. ones are always last. */
    }
    return (bit_ctr[code_size]==0)?1:0;
}

INLINE unsigned char ProbGetBit(unsigned char context){
    unsigned char state=context_states[context];
    unsigned char bit=GolombGetBit(evolution_table[state].code_size);

    if(bit&1){
        context_states[context]=evolution_table[state].LPS_next;
        if(state<2){
            context_MPS[context]^=1;
            return context_MPS[context]; /* just inverted, so just return it */
        } else{
            return context_MPS[context]^1; /* we know bit is 1, so use a constant */
        }
    } else if(bit){
        context_states[context]=evolution_table[state].MPS_next;
        /* zero here, zero there, no difference so drop through. */
    }
    return context_MPS[context]; /* we know bit is 0, so don't bother xoring */
}

INLINE unsigned char GetBit(unsigned char cur_bitplane){
    unsigned char bit;

    bit=ProbGetBit(((cur_bitplane&1)<<4)
                   | ((prev_bits[cur_bitplane]&high_context_bits)>>5)
                   | (prev_bits[cur_bitplane]&low_context_bits));

    prev_bits[cur_bitplane] <<= 1;
    prev_bits[cur_bitplane] |= bit;
    return bit;
}

static unsigned char cur_plane;
static unsigned char num_bits;
static unsigned char next_byte;

void SDD1_init(unsigned char *in){
    bitplane_type=in[0]>>6;

    switch(in[0]&0x30){
      case 0x00:
        high_context_bits=0x01c0;
        low_context_bits =0x0001;
        break;
      case 0x10:
        high_context_bits=0x0180;
        low_context_bits =0x0001;
        break;
      case 0x20:
        high_context_bits=0x00c0;
        low_context_bits =0x0001;
        break;
      case 0x30:
        high_context_bits=0x0180;
        low_context_bits =0x0003;
        break;
    }

    in_stream=(in[0]<<11) | (in[1]<<3);
    valid_bits=5;
    in_buf=in+2;
    memset(bit_ctr, 0, sizeof(bit_ctr));
    memset(context_states, 0, sizeof(context_states));
    memset(context_MPS, 0, sizeof(context_MPS));
    memset(prev_bits, 0, sizeof(prev_bits));

    cur_plane=0;
    num_bits=0;
}

unsigned char SDD1_get_byte(void){
    unsigned char bit;
    unsigned char byte=0;

    switch(bitplane_type){
      case 0:
        num_bits+=16;
        if(num_bits&16){
            next_byte=0;
            for(bit=0x80; bit; bit>>=1){
                if(GetBit(0)) byte |= bit;
                if(GetBit(1)) next_byte |= bit;
            }
            return byte;
        } else {
            return next_byte;
        }

      case 1:
        num_bits+=16;
        if(num_bits&16){
            next_byte=0;
            for(bit=0x80; bit; bit>>=1){
                if(GetBit(cur_plane)) byte |= bit;
                if(GetBit(cur_plane+1)) next_byte |= bit;
            }
            return byte;
        } else {
            if(!num_bits) cur_plane = (cur_plane+2)&7;
            return next_byte;
        }

      case 2:
        num_bits+=16;
        if(num_bits&16){
            next_byte=0;
            for(bit=0x80; bit; bit>>=1){
                if(GetBit(cur_plane)) byte |= bit;
                if(GetBit(cur_plane+1)) next_byte |= bit;
            }
            return byte;
        } else {
            if(!num_bits) cur_plane ^= 2;
            return next_byte;
        }

      case 3:
        for(cur_plane=0, bit=1; bit; bit<<=1, cur_plane++){
            if(GetBit(cur_plane)) byte |= bit;
        }
        return byte;

      default:
        /* should never happen */
        return 0;
    }
}