utext.c

#include <stdio.h>
#include <string.h>
#include <peekpoke.h>

#include "utext.h"

/*
   Decode a VERY constrained subset of ASCII:

   Z-char 0123456789abcdef0123456789abcdef
          --------------------------------
   x-set   ABCDEFGHIJKLMNOPQRSTUVWXYZ?:'!y
   y-set   0123456789ABCDEFGHILMNORSTUWY-x
   
   x = Toggle to the 'x' character set.  Also used to pad end of string if necessary.
   y = Toggle to the 'y' character set.  Also used to pad end of string if necessary.

*/
char *alphabet[2] = { " abcdefghijklmnopqrstuvwxyz?:'!", 
                      " 0123456789abcdefghilmnorstuwy-" };

unsigned char zcase = 0;
unsigned char outbufpos = 0;
unsigned char b0, b1, b2, b3, b4, b5;

void decodeUbyte(unsigned char b, char* outbuf) 
{
   if (b == 31) 
   {
      zcase = 1 - zcase;
      //printf( "%2d : * switch case *\n");
   }
   else
   {
      outbuf[outbufpos] = alphabet[zcase][b];
      //printf( "%2d   %2d.%c\n", b, outbufpos, outbuf[outbufpos] );
      ++outbufpos;
   }
}

char* decodeUtext(unsigned startLoc, char* outbuf)
{
   b5 = 0;
   outbufpos = 0;
   zcase = 0;

   for(; b5 == 0; startLoc += 2)
   {
      b0 = PEEK(startLoc);
      b1 = PEEK(startLoc+1);

      b2 = b0 & 31;
      b3 = (b0/32) + (b1 & 3)*8;
      b4 = (b1 & 127)/4;
      b5 = (b1/128);
  
      decodeUbyte(b2, outbuf);    
      decodeUbyte(b3, outbuf);    
      decodeUbyte(b4, outbuf);    
   }

   outbuf[outbufpos] = 0; // terminate string
   return outbuf;
}

char* decodeUtextbuf(unsigned char *buf, char* outbuf)
{
   unsigned char loc;
   outbufpos = 0; // used by decodeUbyte
   zcase = 0;     // used by decodeUbyte

   for(loc=0; loc<strlen(buf); loc += 2)
   {
      b0 = buf[loc];
      b1 = buf[loc+1];

      b2 = b0 & 31;
      b3 = (b0/32) + (b1 & 3)*8;
      b4 = (b1 & 127)/4;
      b5 = (b1/128);

      decodeUbyte(b2, outbuf);
      decodeUbyte(b3, outbuf);
      decodeUbyte(b4, outbuf);

      if (b5 == 1) break;
   }

   outbuf[outbufpos] = 0; // terminate string
   return outbuf;
}

typedef struct {
      int b0     :5;
      int b1     :5;
      int b2     :5;
      int parity :1;
} ThreeByteCode;

typedef union {
   unsigned int encoded;
   ThreeByteCode asBytes;
} Converter;

// void encodeUtext(char* src, unsigned char* outbuf)
// {
//    unsigned char loc;
//    unsigned char uvalue;
//    zcase     = 0;
//    unsigned char bufpos = 0;
//    unsigned char buf[256];

//    // Convert to 5-bit bytes
//    for(loc=0; loc<strlen(src); loc += 2)
//    {
//       if (!alphabet[zcase][src[loc]]) // switch case
//       {
//          zcase = 1 - zcase;
//          buf[bufpos] = 31;
//          ++bufpos;
//       }
//       buf[bufpos] = alphabet[zcase][src[loc]];
//    }
//
//    // Now compress those bytes
// }

/*
void main()
{
   char buf1[8] = { 162, 12, 171, 79, 224, 62, 146, 145 };
   char buf2[8] = { 137, 34, 79,  58, 46,  76, 244, 201 };
   char outbuf[256];

   decodeUtextbuf( buf1, outbuf );
   printf( "%s\n", outbuf );

   decodeUtextbuf( buf2, outbuf );
   printf( "%s\n", outbuf );
}
*/