rosapps/lib/dflat32/decomp.c

   1 /* ------------------- decomp.c -------------------- */
   2
   3 /*
   4  * Decompress the application.HLP file
   5  * or load the application.TXT file if the .HLP file
   6  * does not exist
   7  */
   8
   9 #include "dflat32/dflat.h"
  10 #include "dflat32/htree.h"
  11
  12 static int in8;
  13 static int ct8 = 8;
  14 static FILE *fi;
  15 static BYTECOUNTER bytectr;
  16 static int LoadingASCII;
  17 struct htr *HelpTree;
  18 static int root;
  19
  20 /* ------- open the help database file -------- */
  21 FILE *OpenHelpFile(void)
  22 {
  23     char *cp;
  24     int treect, i;
  25     char helpname[65];
  26
  27     /* -------- get the name of the help file ---------- */
  28     BuildFileName(helpname, ".hlp");
  29     LoadingASCII = FALSE;
  30     if ((fi = fopen(helpname, "rb")) == NULL)    {
  31         /* ---- no .hlp file, look for .txt file ---- */
  32         if ((cp = strrchr(helpname, '.')) != NULL)    {
  33             strcpy(cp, ".TXT");
  34             fi = fopen(helpname, "rt");
  35         }
  36         if (fi == NULL)
  37             return NULL;
  38         LoadingASCII = TRUE;
  39     }
  40
  41     if (!LoadingASCII && HelpTree == NULL)    {
  42            /* ----- read the byte count ------ */
  43            fread(&bytectr, sizeof bytectr, 1, fi);
  44            /* ----- read the frequency count ------ */
  45            fread(&treect, sizeof treect, 1, fi);
  46            /* ----- read the root offset ------ */
  47            fread(&root, sizeof root, 1, fi);
  48         HelpTree = DFcalloc(treect-256, sizeof(struct htr));
  49         /* ---- read in the tree --- */
  50         for (i = 0; i < treect-256; i++)    {
  51                fread(&HelpTree[i].left,  sizeof(int), 1, fi);
  52             fread(&HelpTree[i].right, sizeof(int), 1, fi);
  53         }
  54     }
  55     return fi;
  56 }
  57
  58 /* ----- read a line of text from the help database ----- */
  59 void *GetHelpLine(char *line)
  60 {
  61     int h;
  62     if (LoadingASCII)   {
  63                 void *hp;
  64                 do
  65                         hp = fgets(line, 160, fi);
  66                 while (*line == ';');
  67                 return hp;
  68         }
  69     *line = '\0';
  70     while (TRUE)    {
  71         /* ----- decompress a line from the file ------ */
  72         h = root;
  73         /* ----- walk the Huffman tree ----- */
  74         while (h > 255)    {
  75             /* --- h is a node pointer --- */
  76             if (ct8 == 8)   {
  77                 /* --- read 8 bits of compressed data --- */
  78                 if ((in8 = fgetc(fi)) == EOF)    {
  79                     *line = '\0';
  80                     return NULL;
  81                 }
  82                 ct8 = 0;
  83             }
  84             /* -- point to left or right node based on msb -- */
  85             if (in8 & 0x80)
  86                 h = HelpTree[h-256].left;
  87             else
  88                 h = HelpTree[h-256].right;
  89             /* --- shift the next bit in --- */
  90             in8 <<= 1;
  91             ct8++;
  92         }
  93         /* --- h < 255 = decompressed character --- */
  94         if (h == '\r')
  95             continue;    /* skip the '\r' character */
  96         /* --- put the character in the buffer --- */
  97         *line++ = h;
  98         /* --- if '\n', end of line --- */
  99         if (h == '\n')
 100             break;
 101     }
 102     *line = '\0';    /* null-terminate the line */
 103     return line;
 104 }
 105
 106 /* --- compute the database file byte and bit position --- */
 107 void HelpFilePosition(long *offset, int *bit)
 108 {
 109     *offset = ftell(fi);
 110     if (LoadingASCII)
 111         *bit = 0;
 112     else    {
 113         if (ct8 < 8)
 114             --*offset;
 115         *bit = ct8;
 116     }
 117 }
 118
 119 /* -- position the database to the specified byte and bit -- */
 120 void SeekHelpLine(long offset, int bit)
 121 {
 122     int i;
 123     fseek(fi, offset, 0);
 124     if (!LoadingASCII)    {
 125         ct8 = bit;
 126         if (ct8 < 8)    {
 127             in8 = fgetc(fi);
 128             for (i = 0; i < bit; i++)
 129                 in8 <<= 1;
 130         }
 131     }
 132 }
 133
 134