disk8: Initial commit

[pdp8.git] / sw / disk8 / src / ops.c

#include <stdio.h>
#include "structures.h"
#include "ops.h"

/*
 * Pack an OS/8 filename into 6 bit code, 2 digits per 12 bit word.
 * Argument is a zero-terminated string, containing the full name with
 * the dot, i.E. "XXXXXX.YY",0 is the legal form.
 */
void os8_file_name_pack(os8_file_name_t * filename, char * data){
  
  /* Read and write positions */
  int inpos=0, outpos=0;

  /* Zero out all data in target */
  for (outpos=0; outpos<4; outpos++) filename->data[outpos]=0;

  for (outpos=0; outpos<8 && data[inpos];){
    if (data[inpos]=='.'){
      inpos++;
      if (outpos<6) outpos=6;
      continue;
    }
    filename->data[outpos/2] |= os8_ascii2pdp(data[inpos++]) << ((!(outpos%2))*6);
    outpos++;
  }    
}

void os8_file_name_extract(os8_file_name_t * filename, char * data){
  
  /* Read and write positions */
  int inpos=0, outpos=0;

  for (inpos=0; inpos<8; inpos++){

    unsigned short int current=filename->data[inpos/2]; /* Get right word */
    if (!(inpos%2)) current >>= 6;
    current &= 077;

    if ((!current) && ((inpos==0)||(inpos==6))){ /* Empty file name or extension*/
      data[outpos]=0;                            /* Terminate file name in buffer */
      break;                                     /* Leave the loop! */
    }

    if (inpos==6){
      data[outpos++]='.';          /* Insert dot into new name */
    }
    
    if (current) {                 /* Insert character into output */
      data[outpos++]=os8_pdp2ascii(current);
    }
  }
  data[outpos]=0;                  /* Terminate string. */
}

/* Pack one character into 6 bit OS/8 reduced ASCII code */
unsigned char os8_ascii2pdp(unsigned char inchar){
  unsigned char result=inchar & 077;  /* Strip upper bits */
  return result;
}

/* Extract one character from 6 bit OS/8 reduced ASCII code */
unsigned char os8_pdp2ascii(unsigned char inchar){
  inchar &=077;
  if (inchar<040) return inchar|0100;
  return inchar;
}

/* Negate a p8word */
p8word p8_neg(p8word in){
  return (-in)&07777;
}

/* Twist the bytes for little endian machines */
p8word p8_twist(p8word in){
  return (in&0xff)<<8 | ((in>>8)&0xff);
}