xdecode.c

来自「Reference Implementation of G.711 standa」· C语言 代码 · 共 1,011 行 · 第 1/3 页

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        char *get_header (FILE *fp, char *buffer, int max_len);
             ~~~~~~~~~~~

	Description:
	~~~~~~~~~~~~
        Sistematically reads lines from "fp" until one checks with the
        standard expected ty uudecode algorithm. Important to skip
        additional lines added by e-mail protocols (as BSMTP) for
        routing information, and that have no information as far as the
        original file is concerned.

	Variables:
	~~~~~~~~~~
	fp 	pointer to encoded file
        buffer	buffer where the header line is returned
        max_len maximum length for header.

	Exit values:
	~~~~~~~~~~~~
	Pointer to header's buffer; NULL if no header found in file.

	Author:	Simao Ferraz de Campos Neto -- CPqD/Telebras
	~~~~~~~  <[e-mail]>

	Date:	19/Mar/91-16:30
	~~~~~

	Version: 1.00
	~~~~~~~~

	Revision/Date/Author: none (yet)
	~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
char           *get_header(fp, buffer, max_len)
  FILE           *fp;
  char           *buffer;
  int             max_len;
{
  for (;;)
  {
    if (fgets(buffer, max_len, fp) == NULL)
      return (NULL);
    if (strncmp(buffer, "begin ", 6) == 0)
      break;
  }
  return (buffer);
}

/*
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	char *translate_destination (char *dest);
	     ~~~~~~~~~~~~~~~~~~~~~~

	Description:
	~~~~~~~~~~~~
	Handle ~user/file format, converting to present system's names
	(root, directory, user, etc) IF not under MSDOS or VAX-VMS
	(ie, Unix); if one of the former, no modification on "dest"
	is performed.

	Variables:
	~~~~~~~~~~
        dest	i/o buffer where the translation is performed

	Exit values:
	~~~~~~~~~~~~
	Pointer to translated buffer

	Author:	unknown
	~~~~~~~

	Revision/Date/Author: Simao Ferraz de Campos Neto -- CPqD/Telebras
	~~~~~~~~~~~~~~~~~~~~~  <[e-mail]> 19/Mar/91-16:30

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
char           *translate_destination(dest)
  char           *dest;
{
#ifndef MSDOS
#ifndef VMS
  char           *sl;
  struct passwd  *getpwnam();
  struct passwd  *user;
  char            dnbuf[100];


  sl = xd_index(dest, '/');
  if (sl == NULL)
    return (NULL);

  *sl++ = 0;
  user = getpwnam(dest + 1);
  if (user == NULL)
    return (NULL);

  strcpy(dnbuf, user->pw_dir);
  strcat(dnbuf, "/");
  strcat(dnbuf, sl);
  strcpy(dest, dnbuf);
#endif				/* VMS */
#endif				/* MSDOS */

  return (dest);
}

/*
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	decode (FILE *in, FILE *out);
        ~~~~~~~

	Description:
	~~~~~~~~~~~~
	Copy from in to out, encoding as it goes along, using the basic
	decoding scheme:
                          DEC(c) = (((c) - ' ') & 077)

        Variables:
	~~~~~~~~~~
	in 	pointer to file from which samples are taken
	out	pointer to file to which encoded samples are put

	Return values:
	~~~~~~~~~~~~~~
	1,  if success;
	0,  if EOF while expecting to have more data;
	-1,  on other file read failures;
	2,  if a bug was found.

	Routines:	- outdec
	~~~~~~~~~	- DEC

	Author:	original, unknown; got from PD sources.
	~~~~~~~

	Revision/Date/Author:
	~~~~~~~~~~~~~~~~~~~~~
	19.Mar.91  v1.0	Documentation of the public domain source for decode();
			<[e-mail]>
	31.Aug.92  v1.1 Corrected bug in dealing with lines that, originally
			with a space as the very last character in the
			line, had this space stripped-off by the
			e-mailing system (somewhere!). Here, a new
			blank is put at the end of the line, replacing
			the CR character normally present.
			<[e-mail]>

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
int decode(in, out)
  FILE           *in;
  FILE           *out;
{
  char            buf[80];
  char           *bp;
  int             n, i, expected;
  static unsigned long lineno;
  int             out_code = 1;

  for (;; ++lineno)
  {
    /* for each input line */
    if (fgets(buf, sizeof buf, in) == NULL)
    {				/* An error occurred */
      if (feof(in))
	return (0);
      else
	return (-1);
    }
    n = DEC(buf[0]);

    /* Break if no chars to read */
    if ((n <= 0) || (buf[0] == '\n'))
      break;

    /* Calculate expected # of chars and pad if necessary */
    expected = ((n + 2) / 3) << 2;
    for (i = strlen(buf) - 1; i <= expected; i++)
      buf[i] = ' ';

    /* Move pointer to start of data */
    bp = &buf[1];
    while (n > 0)
    {
      outdec(bp, out, n);
      bp += 4;
      n -= 3;
    }
  }
  return (out_code);
}

/*
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	int outdec (char *p, FILE *f, int n);
            ~~~~~~

        Description:
        ~~~~~~~~~~~~
        Output a  group of  3  bytes (4 input characters). The input
        chars  are pointed to by p, they are to be output to file f.
        n is used to tell us not to output all of them at the end of
        the file.

        The basic decoding algorithm is:
                        DEC(c) = (((c) - ' ') & 077)


	Variables:
	~~~~~~~~~~
	p	pointer to array of 4 [printable] bytes to be decoded
		and saved as 3 binary bytes;
	f	pointer to file to which decoded samples are put
        n	expected number of chars in the line

	Author:	unknown
	~~~~~~~

	Revision/Date/Author: Simao Ferraz de Campos Neto -- CPqD/Telebras
	~~~~~~~~~~~~~~~~~~~~~ <[e-mail]> -- 19/Mar/91-16:30

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
int             outdec(p, f, n)
  char           *p;
  FILE           *f;
  int             n;
{
  char            c[3];

  /* Decode chars */
  c[0] = DEC(*p) << 2 | DEC(p[1]) >> 4;
  c[1] = DEC(p[1]) << 4 | DEC(p[2]) >> 2;
  c[2] = DEC(p[2]) << 6 | DEC(p[3]);

  /* Save decoded bytes on file */
  if (n >= 1)
    putc(c[0], f);
  if (n >= 2)
    putc(c[1], f);
  if (n >= 3)
    putc(c[2], f);

  /* Update CRCs */
  if (n > 3)
    n = 3;
  crc_a = get_arc_crc(crc_a, (unsigned char *) c, n);
  crc_c = get_ccitt_crc(crc_c, (unsigned char *) c, n);
  crc_x = get_xmodem_crc(crc_x, (unsigned char *) c, n);

  /* Return OK */
  return 0;
}

/*
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	int fr (FILE *fd, char *buf, int cnt);
	    ~~

	Description:
	~~~~~~~~~~~~
	Read upto cnt bytes from stream (file/device) pointed by fd and
	save in buffer buf. Similar to fread.

	Variables:
	~~~~~~~~~~
	fd 	pointer to file from which chars are read
	buf	pointer to char
	cnt	maximum number of chars to be read

	Author:	unknown
	~~~~~~~

	Revision/Date/Author: Simao Ferraz de Campos Neto -- CPqD/Telebras
	~~~~~~~~~~~~~~~~~~~~~ <[e-mail]> -- 19/Mar/91-16:30

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
int             fr(fd, buf, cnt)
  FILE           *fd;
  char           *buf;
  int             cnt;
{
  int             c, i;

  for (i = 0; i < cnt; i++)
  {
    c = getc(fd);
    if (c == EOF)
      return (i);
    buf[i] = c;
  }
  return (cnt);
}

/*
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	char *xd_index (register char *sp, register char c);
	     ~~~~~~

	Description:
	~~~~~~~~~~~~
	Locates the first occurence of c in stream sp and returns it;
	if c is not found, returns NULL.

	Variables:
	~~~~~~~~~~
	sp 	pointer to first ocurrence of c in ptr
	c	character to be located;

	Author:	unknown
	~~~~~~~

	Revision/Date/Author: Simao Ferraz de Campos Neto -- CPqD/Telebras
	~~~~~~~~~~~~~~~~~~~~~ <[e-mail]> -- 19/Mar/91-16:30

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
#ifdef NULL
#undef NULL
#endif
#define NULL    0
char           *xd_index(sp, c)
  register char  *sp;
  register char   c;
{
  do
  {
    if (*sp == c)
      return (sp);
  } while (*sp++);
  return (NULL);
}
/* ....................... End of xd_index() ................................ */