/*
** getrel -- read a relocatable-object file
*/
#include <stdio.h>
#include "rel.h"
#include "mac.h"

/*
** get next REL item
** return itemcode on success, ERR on error
** on successful return:
**    item = item code
**    type = type of field
**   field = value of field
**  symbol = symbol name
*/
getrel() {
  if(!getbits(1)) return (ERR);		/* get 1 bit */
  if(field == 0) {			/* absolute item */
    if(!getbits(8)) return (ERR);	/* get next 8 bits */
    return (type = item = ABS);		/* absolute item */
    }
  if(!getbits(2)) return (ERR);		/* get next 2 bits */
  switch(type = item = field) {
    case 0: return (getspec());		/* special link item */
    case 1:				/* program relative item */
    case 2:				/* data relative item */
    case 3:				/* common relative item */
    }
  if(getfld() == ERR) return (ERR);	/* get next 16 bits */
  return (item);			/* relative items */
  }

getspec() {				/* get next special item */
  if(!getbits(4)) return (ERR);		/* get next 4 bits */
  type = ABS;				/* default type */
  item = field + 4;
  switch(field) {
    case 0:	/* entry symbol */
    case 1:	/* select common block */
    case 2:	/* program name */
    case 3:	/* request library search */
    case 4:	/* extension link items */
      if(getsym() == ERR) return (ERR);
      break;
    case 5:	/* define common size */
    case 6:	/* head of external reference chain */
    case 7:	/* define entry point */
      if(gettyp() == ERR || getfld() == ERR || getsym() == ERR) return (ERR);
      break;
    case 8:	/* external - offset */
    case 9:     /* external + offset */
    case 10:	/* size of data area */
    case 11:	/* set loading location counter */
    case 12:	/* chain addr (fill chain with lc) */
    case 13:    /* size of program */
      if(gettyp() == ERR || getfld() == ERR) return (ERR);
      break;
    case 14:	/* end of program */
      if(gettyp() == ERR || getfld() == ERR) return (ERR);
      inrem = 0;	/* force byte boundary */
      break;
    case 15:	/* end of file */
      inrem = 0;	/* force byte boundary */
    }
  return (item);
  }

gettyp() {
  if(!getbits(2)) return (ERR);		/* get 2-bit field type */
  return (type = field);
  }

getfld() {				/* get type and value of field */
  int low;
  if(!getbits(8)) return (ERR);		/* get first 8 bits */
  low = field;				/* save as low order byte */
  if(!getbits(8)) return (ERR);		/* get next 8 bits */
  field = (field << 8) | low;		/* combine high & low bytes */
  return (item);
  }

getsym() {				/* get symbol */
  int i, save; char *cp;
  cp = symbol;
  save = field;				/* save field */
  if(!getbits(3)) return (ERR);		/* get 3-bit symbol length */
  i = field;				/* capture symbol length */
  while(i--) {
    if(!getbits(8)) return (ERR);	/* get next byte */
    *cp++ = field;
    }
  *cp = NULL;				/* terminate symbol */
  field = save;				/* restore field */
  return (item);
  }

/*
** get next n bits from REL file into "field"
** return true on success, false on error
*/
getbits(n) int n; {
  int get;
  field = 0;				/* initialize result */
  while(n) {				/* more bits to fetch */
    if(inrem == 0) {			/* need another chunk */
      if(read(inrel, &inchunk, 1) != 1) {	/* get next bit cluster */
	fputs("\n\7- Abnormal End of REL File\n", stdout);
	return (NO);			/* failure */
	}
      inrem = 8;			/* 8 bits remaim */
      }
    if(n > inrem) get = inrem; else get = n; /* how many from this chunk */
    n     -= get;			/* decrement bits needed */
    inrem -= get;			/* decr remaining bits */
    field  = (field << get) +
	     ((inchunk >> inrem) & ~(ONES << get));
    }
  return (YES);
  }