[comp.os.minix] Fix to bug in sum.c

ast@cs.vu.nl (Andy Tanenbaum) (09/14/87)

I have found and fixed a bug in sum.c.  An internal variable overflowed on
files > 32K.  The file is so short that here is the complete new file:

Andy Tanenbaum (ast@cs.vu.nl)

--------------------------------- sum.c -------------------------------
/* sum - checksum a file		Author: Martin C. Atkins */

/*
 *	This program was written by:
 *		Martin C. Atkins,
 *		University of York,
 *		Heslington,
 *		York. Y01 5DD
 *		England
 *	and is released into the public domain, on the condition
 *	that this comment is always included without alteration.
 */

#define BUFSIZ (512)

int rc = 0;

char *defargv[] = { "-", 0 };

main(argc,argv)
int argc;
char *argv[];
{
  int fd;

  if (*++argv == 0)
	argv = defargv;
  for (; *argv; argv++) {
	if (argv[0][0] == '-' && argv[0][1] == '\0')
		fd = 0;
	else
		fd = open(*argv, 0);

	if (fd == -1) {
		error("can't open ",*argv);
		rc = 1;
		continue;
	}
	sum(fd, (argc > 2) ? *argv : (char *)0);
	if (fd != 0) close(fd);
  }
  exit(rc);
}

error(s,f)
char *s,*f;
{

  std_err("sum: ");
  std_err(s);

  if (f) std_err(f);
  std_err("\n");
}

sum(fd,fname)
int fd;
char *fname;
{
  char buf[BUFSIZ];
  int i,n;
  long size = 0;
  unsigned crc = 0;
  unsigned tmp, blks;

  while((n = read(fd,buf,BUFSIZ)) > 0) {
	for (i = 0; i < n; i++) {
		crc = (crc>>1) + ((crc&1) ? 0x8000 : 0);
		tmp = buf[i] & 0377;
		crc += tmp;
		crc &= 0xffff;
		size++;
	}
  }

  if (n < 0) {
	if (fname)
		error("read error on ", fname);
	else
		error("read error", (char *)0);
	rc = 1;
	return;
  }
  putd(crc,5,1);
  blks = (size + (long)BUFSIZ - 1L)/(long)BUFSIZ;
  putd(blks, 6, 0);
  if (fname) prints(" %s", fname);
  prints("\n");
}

putd(number, fw, zeros)
int number,fw,zeros;
{
/* Put a decimal number, in a field width, to stdout. */

  char buf[10];
  int n;
  unsigned num;

  num = (unsigned) number;
  for (n = 0; n < fw; n++) {
	if (num || n == 0) {
		buf[fw-n-1] = '0' + num%10;
		num /= 10;
	} else
		buf[fw-n-1] = zeros ? '0' : ' ';
  }
  buf[fw] = 0;
  prints("%s", buf);
}