sw/disk8/src/ops.c

   1
   2 #include <stdio.h>
   3 #include "structures.h"
   4 #include "ops.h"
   5
   6 /*
   7  * Pack an OS/8 filename into 6 bit code, 2 digits per 12 bit word.
   8  * Argument is a zero-terminated string, containing the full name with
   9  * the dot, i.E. "XXXXXX.YY",0 is the legal form.
  10  */
  11 void os8_file_name_pack(os8_file_name_t * filename, char * data){
  12
  13   /* Read and write positions */
  14   int inpos=0, outpos=0;
  15
  16   /* Zero out all data in target */
  17   for (outpos=0; outpos<4; outpos++) filename->data[outpos]=0;
  18
  19   for (outpos=0; outpos<8 && data[inpos];){
  20     if (data[inpos]=='.'){
  21       inpos++;
  22       if (outpos<6) outpos=6;
  23       continue;
  24     }
  25     filename->data[outpos/2] |= os8_ascii2pdp(data[inpos++]) << ((!(outpos%2))*6);
  26     outpos++;
  27   }
  28 }
  29
  30 void os8_file_name_extract(os8_file_name_t * filename, char * data){
  31
  32   /* Read and write positions */
  33   int inpos=0, outpos=0;
  34
  35   for (inpos=0; inpos<8; inpos++){
  36
  37     unsigned short int current=filename->data[inpos/2]; /* Get right word */
  38     if (!(inpos%2)) current >>= 6;
  39     current &= 077;
  40
  41     if ((!current) && ((inpos==0)||(inpos==6))){ /* Empty file name or extension*/
  42       data[outpos]=0;                            /* Terminate file name in buffer */
  43       break;                                     /* Leave the loop! */
  44     }
  45
  46     if (inpos==6){
  47       data[outpos++]='.';          /* Insert dot into new name */
  48     }
  49
  50     if (current) {                 /* Insert character into output */
  51       data[outpos++]=os8_pdp2ascii(current);
  52     }
  53   }
  54   data[outpos]=0;                  /* Terminate string. */
  55 }
  56
  57 /* Pack one character into 6 bit OS/8 reduced ASCII code */
  58 unsigned char os8_ascii2pdp(unsigned char inchar){
  59   unsigned char result=inchar & 077;  /* Strip upper bits */
  60   return result;
  61 }
  62
  63 /* Extract one character from 6 bit OS/8 reduced ASCII code */
  64 unsigned char os8_pdp2ascii(unsigned char inchar){
  65   inchar &=077;
  66   if (inchar<040) return inchar|0100;
  67   return inchar;
  68 }
  69
  70 /* Negate a p8word */
  71 p8word p8_neg(p8word in){
  72   return (-in)&07777;
  73 }
  74
  75 /* Twist the bytes for little endian machines */
  76 p8word p8_twist(p8word in){
  77   return (in&0xff)<<8 | ((in>>8)&0xff);
  78 }
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