wrjpgcom.c - third_party/libjpeg-turbo - Git at Google

 /*
  * wrjpgcom.c
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1994-1997, Thomas G. Lane.
  * libjpeg-turbo Modifications:
  * Copyright (C) 2014, D. R. Commander
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
  * This file contains a very simple stand-alone application that inserts
  * user-supplied text as a COM (comment) marker in a JFIF file.
  * This may be useful as an example of the minimum logic needed to parse
  * JPEG markers.
  */

 #define JPEG_CJPEG_DJPEG        /* to get the command-line config symbols */
 #include "jinclude.h"           /* get auto-config symbols, <stdio.h> */

 #ifndef HAVE_STDLIB_H           /* <stdlib.h> should declare malloc() */
 extern void * malloc ();
 #endif
 #include <ctype.h>              /* to declare isupper(), tolower() */
 #ifdef USE_SETMODE
 #include <fcntl.h>              /* to declare setmode()'s parameter macros */
 /* If you have setmode() but not <io.h>, just delete this line: */
 #include <io.h>                 /* to declare setmode() */
 #endif

 #ifdef USE_CCOMMAND             /* command-line reader for Macintosh */
 #ifdef __MWERKS__
 #include <SIOUX.h>              /* Metrowerks needs this */
 #include <console.h>            /* ... and this */
 #endif
 #ifdef THINK_C
 #include <console.h>            /* Think declares it here */
 #endif
 #endif

 #ifdef DONT_USE_B_MODE          /* define mode parameters for fopen() */
 #define READ_BINARY     "r"
 #define WRITE_BINARY    "w"
 #else
 #define READ_BINARY     "rb"
 #define WRITE_BINARY    "wb"
 #endif

 #ifndef EXIT_FAILURE            /* define exit() codes if not provided */
 #define EXIT_FAILURE  1
 #endif
 #ifndef EXIT_SUCCESS
 #define EXIT_SUCCESS  0
 #endif

 /* Reduce this value if your malloc() can't allocate blocks up to 64K.
  * On DOS, compiling in large model is usually a better solution.
  */

 #ifndef MAX_COM_LENGTH
 #define MAX_COM_LENGTH 65000L   /* must be <= 65533 in any case */
 #endif


 /*
  * These macros are used to read the input file and write the output file.
  * To reuse this code in another application, you might need to change these.
  */

 static FILE * infile;           /* input JPEG file */

 /* Return next input byte, or EOF if no more */
 #define NEXTBYTE()  getc(infile)

 static FILE * outfile;          /* output JPEG file */

 /* Emit an output byte */
 #define PUTBYTE(x)  putc((x), outfile)


 /* Error exit handler */
 #define ERREXIT(msg)  (fprintf(stderr, "%s\n", msg), exit(EXIT_FAILURE))


 /* Read one byte, testing for EOF */
 static int
 read_1_byte (void)
 {
   int c;

   c = NEXTBYTE();
   if (c == EOF)
     ERREXIT("Premature EOF in JPEG file");
   return c;
 }

 /* Read 2 bytes, convert to unsigned int */
 /* All 2-byte quantities in JPEG markers are MSB first */
 static unsigned int
 read_2_bytes (void)
 {
   int c1, c2;

   c1 = NEXTBYTE();
   if (c1 == EOF)
     ERREXIT("Premature EOF in JPEG file");
   c2 = NEXTBYTE();
   if (c2 == EOF)
     ERREXIT("Premature EOF in JPEG file");
   return (((unsigned int) c1) << 8) + ((unsigned int) c2);
 }


 /* Routines to write data to output file */

 static void
 write_1_byte (int c)
 {
   PUTBYTE(c);
 }

 static void
 write_2_bytes (unsigned int val)
 {
   PUTBYTE((val >> 8) & 0xFF);
   PUTBYTE(val & 0xFF);
 }

 static void
 write_marker (int marker)
 {
   PUTBYTE(0xFF);
   PUTBYTE(marker);
 }

 static void
 copy_rest_of_file (void)
 {
   int c;

   while ((c = NEXTBYTE()) != EOF)
     PUTBYTE(c);
 }


 /*
  * JPEG markers consist of one or more 0xFF bytes, followed by a marker
  * code byte (which is not an FF).  Here are the marker codes of interest
  * in this program.  (See jdmarker.c for a more complete list.)
  */

 #define M_SOF0  0xC0            /* Start Of Frame N */
 #define M_SOF1  0xC1            /* N indicates which compression process */
 #define M_SOF2  0xC2            /* Only SOF0-SOF2 are now in common use */
 #define M_SOF3  0xC3
 #define M_SOF5  0xC5            /* NB: codes C4 and CC are NOT SOF markers */
 #define M_SOF6  0xC6
 #define M_SOF7  0xC7
 #define M_SOF9  0xC9
 #define M_SOF10 0xCA
 #define M_SOF11 0xCB
 #define M_SOF13 0xCD
 #define M_SOF14 0xCE
 #define M_SOF15 0xCF
 #define M_SOI   0xD8            /* Start Of Image (beginning of datastream) */
 #define M_EOI   0xD9            /* End Of Image (end of datastream) */
 #define M_SOS   0xDA            /* Start Of Scan (begins compressed data) */
 #define M_COM   0xFE            /* COMment */


 /*
  * Find the next JPEG marker and return its marker code.
  * We expect at least one FF byte, possibly more if the compressor used FFs
  * to pad the file.  (Padding FFs will NOT be replicated in the output file.)
  * There could also be non-FF garbage between markers.  The treatment of such
  * garbage is unspecified; we choose to skip over it but emit a warning msg.
  * NB: this routine must not be used after seeing SOS marker, since it will
  * not deal correctly with FF/00 sequences in the compressed image data...
  */

 static int
 next_marker (void)
 {
   int c;
   int discarded_bytes = 0;

   /* Find 0xFF byte; count and skip any non-FFs. */
   c = read_1_byte();
   while (c != 0xFF) {
     discarded_bytes++;
     c = read_1_byte();
   }
   /* Get marker code byte, swallowing any duplicate FF bytes.  Extra FFs
    * are legal as pad bytes, so don't count them in discarded_bytes.
    */
   do {
     c = read_1_byte();
   } while (c == 0xFF);

   if (discarded_bytes != 0) {
     fprintf(stderr, "Warning: garbage data found in JPEG file\n");
   }

   return c;
 }


 /*
  * Read the initial marker, which should be SOI.
  * For a JFIF file, the first two bytes of the file should be literally
  * 0xFF M_SOI.  To be more general, we could use next_marker, but if the
  * input file weren't actually JPEG at all, next_marker might read the whole
  * file and then return a misleading error message...
  */

 static int
 first_marker (void)
 {
   int c1, c2;

   c1 = NEXTBYTE();
   c2 = NEXTBYTE();
   if (c1 != 0xFF || c2 != M_SOI)
     ERREXIT("Not a JPEG file");
   return c2;
 }


 /*
  * Most types of marker are followed by a variable-length parameter segment.
  * This routine skips over the parameters for any marker we don't otherwise
  * want to process.
  * Note that we MUST skip the parameter segment explicitly in order not to
  * be fooled by 0xFF bytes that might appear within the parameter segment;
  * such bytes do NOT introduce new markers.
  */

 static void
 copy_variable (void)
 /* Copy an unknown or uninteresting variable-length marker */
 {
   unsigned int length;

   /* Get the marker parameter length count */
   length = read_2_bytes();
   write_2_bytes(length);
   /* Length includes itself, so must be at least 2 */
   if (length < 2)
     ERREXIT("Erroneous JPEG marker length");
   length -= 2;
   /* Skip over the remaining bytes */
   while (length > 0) {
     write_1_byte(read_1_byte());
     length--;
   }
 }

 static void
 skip_variable (void)
 /* Skip over an unknown or uninteresting variable-length marker */
 {
   unsigned int length;

   /* Get the marker parameter length count */
   length = read_2_bytes();
   /* Length includes itself, so must be at least 2 */
   if (length < 2)
     ERREXIT("Erroneous JPEG marker length");
   length -= 2;
   /* Skip over the remaining bytes */
   while (length > 0) {
     (void) read_1_byte();
     length--;
   }
 }


 /*
  * Parse the marker stream until SOFn or EOI is seen;
  * copy data to output, but discard COM markers unless keep_COM is true.
  */

 static int
 scan_JPEG_header (int keep_COM)
 {
   int marker;

   /* Expect SOI at start of file */
   if (first_marker() != M_SOI)
     ERREXIT("Expected SOI marker first");
   write_marker(M_SOI);

   /* Scan miscellaneous markers until we reach SOFn. */
   for (;;) {
     marker = next_marker();
     switch (marker) {
       /* Note that marker codes 0xC4, 0xC8, 0xCC are not, and must not be,
        * treated as SOFn.  C4 in particular is actually DHT.
        */
     case M_SOF0:                /* Baseline */
     case M_SOF1:                /* Extended sequential, Huffman */
     case M_SOF2:                /* Progressive, Huffman */
     case M_SOF3:                /* Lossless, Huffman */
     case M_SOF5:                /* Differential sequential, Huffman */
     case M_SOF6:                /* Differential progressive, Huffman */
     case M_SOF7:                /* Differential lossless, Huffman */
     case M_SOF9:                /* Extended sequential, arithmetic */
     case M_SOF10:               /* Progressive, arithmetic */
     case M_SOF11:               /* Lossless, arithmetic */
     case M_SOF13:               /* Differential sequential, arithmetic */
     case M_SOF14:               /* Differential progressive, arithmetic */
     case M_SOF15:               /* Differential lossless, arithmetic */
       return marker;

     case M_SOS:                 /* should not see compressed data before SOF */
       ERREXIT("SOS without prior SOFn");
       break;

     case M_EOI:                 /* in case it's a tables-only JPEG stream */
       return marker;

     case M_COM:                 /* Existing COM: conditionally discard */
       if (keep_COM) {
         write_marker(marker);
         copy_variable();
       } else {
         skip_variable();
       }
       break;

     default:                    /* Anything else just gets copied */
       write_marker(marker);
       copy_variable();          /* we assume it has a parameter count... */
       break;
     }
   } /* end loop */
 }


 /* Command line parsing code */

 static const char * progname;   /* program name for error messages */


 static void
 usage (void)
 /* complain about bad command line */
 {
   fprintf(stderr, "wrjpgcom inserts a textual comment in a JPEG file.\n");
   fprintf(stderr, "You can add to or replace any existing comment(s).\n");

   fprintf(stderr, "Usage: %s [switches] ", progname);
 #ifdef TWO_FILE_COMMANDLINE
   fprintf(stderr, "inputfile outputfile\n");
 #else
   fprintf(stderr, "[inputfile]\n");
 #endif

   fprintf(stderr, "Switches (names may be abbreviated):\n");
   fprintf(stderr, "  -replace         Delete any existing comments\n");
   fprintf(stderr, "  -comment \"text\"  Insert comment with given text\n");
   fprintf(stderr, "  -cfile name      Read comment from named file\n");
   fprintf(stderr, "Notice that you must put quotes around the comment text\n");
   fprintf(stderr, "when you use -comment.\n");
   fprintf(stderr, "If you do not give either -comment or -cfile on the command line,\n");
   fprintf(stderr, "then the comment text is read from standard input.\n");
   fprintf(stderr, "It can be multiple lines, up to %u characters total.\n",
           (unsigned int) MAX_COM_LENGTH);
 #ifndef TWO_FILE_COMMANDLINE
   fprintf(stderr, "You must specify an input JPEG file name when supplying\n");
   fprintf(stderr, "comment text from standard input.\n");
 #endif

   exit(EXIT_FAILURE);
 }


 static int
 keymatch (char * arg, const char * keyword, int minchars)
 /* Case-insensitive matching of (possibly abbreviated) keyword switches. */
 /* keyword is the constant keyword (must be lower case already), */
 /* minchars is length of minimum legal abbreviation. */
 {
   register int ca, ck;
   register int nmatched = 0;

   while ((ca = *arg++) != '\0') {
     if ((ck = *keyword++) == '\0')
       return 0;                 /* arg longer than keyword, no good */
     if (isupper(ca))            /* force arg to lcase (assume ck is already) */
       ca = tolower(ca);
     if (ca != ck)
       return 0;                 /* no good */
     nmatched++;                 /* count matched characters */
   }
   /* reached end of argument; fail if it's too short for unique abbrev */
   if (nmatched < minchars)
     return 0;
   return 1;                     /* A-OK */
 }


 /*
  * The main program.
  */

 int
 main (int argc, char **argv)
 {
   int argn;
   char * arg;
   int keep_COM = 1;
   char * comment_arg = NULL;
   FILE * comment_file = NULL;
   unsigned int comment_length = 0;
   int marker;

   /* On Mac, fetch a command line. */
 #ifdef USE_CCOMMAND
   argc = ccommand(&argv);
 #endif

   progname = argv[0];
   if (progname == NULL || progname[0] == 0)
     progname = "wrjpgcom";      /* in case C library doesn't provide it */

   /* Parse switches, if any */
   for (argn = 1; argn < argc; argn++) {
     arg = argv[argn];
     if (arg[0] != '-')
       break;                    /* not switch, must be file name */
     arg++;                      /* advance over '-' */
     if (keymatch(arg, "replace", 1)) {
       keep_COM = 0;
     } else if (keymatch(arg, "cfile", 2)) {
       if (++argn >= argc) usage();
       if ((comment_file = fopen(argv[argn], "r")) == NULL) {
         fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
         exit(EXIT_FAILURE);
       }
     } else if (keymatch(arg, "comment", 1)) {
       if (++argn >= argc) usage();
       comment_arg = argv[argn];
       /* If the comment text starts with '"', then we are probably running
        * under MS-DOG and must parse out the quoted string ourselves.  Sigh.
        */
       if (comment_arg[0] == '"') {
         comment_arg = (char *) malloc((size_t) MAX_COM_LENGTH);
         if (comment_arg == NULL)
           ERREXIT("Insufficient memory");
         if (strlen(argv[argn]) + 2 >= (size_t) MAX_COM_LENGTH) {
           fprintf(stderr, "Comment text may not exceed %u bytes\n",
                   (unsigned int) MAX_COM_LENGTH);
           exit(EXIT_FAILURE);
         }
         strcpy(comment_arg, argv[argn]+1);
         for (;;) {
           comment_length = (unsigned int) strlen(comment_arg);
           if (comment_length > 0 && comment_arg[comment_length-1] == '"') {
             comment_arg[comment_length-1] = '\0'; /* zap terminating quote */
             break;
           }
           if (++argn >= argc)
             ERREXIT("Missing ending quote mark");
           if (strlen(comment_arg) + strlen(argv[argn]) + 2 >=
               (size_t) MAX_COM_LENGTH) {
             fprintf(stderr, "Comment text may not exceed %u bytes\n",
                     (unsigned int) MAX_COM_LENGTH);
             exit(EXIT_FAILURE);
           }
           strcat(comment_arg, " ");
           strcat(comment_arg, argv[argn]);
         }
       } else if (strlen(argv[argn]) >= (size_t) MAX_COM_LENGTH) {
         fprintf(stderr, "Comment text may not exceed %u bytes\n",
                 (unsigned int) MAX_COM_LENGTH);
         exit(EXIT_FAILURE);
       }
       comment_length = (unsigned int) strlen(comment_arg);
     } else
       usage();
   }

   /* Cannot use both -comment and -cfile. */
   if (comment_arg != NULL && comment_file != NULL)
     usage();
   /* If there is neither -comment nor -cfile, we will read the comment text
    * from stdin; in this case there MUST be an input JPEG file name.
    */
   if (comment_arg == NULL && comment_file == NULL && argn >= argc)
     usage();

   /* Open the input file. */
   if (argn < argc) {
     if ((infile = fopen(argv[argn], READ_BINARY)) == NULL) {
       fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
       exit(EXIT_FAILURE);
     }
   } else {
     /* default input file is stdin */
 #ifdef USE_SETMODE              /* need to hack file mode? */
     setmode(fileno(stdin), O_BINARY);
 #endif
 #ifdef USE_FDOPEN               /* need to re-open in binary mode? */
     if ((infile = fdopen(fileno(stdin), READ_BINARY)) == NULL) {
       fprintf(stderr, "%s: can't open stdin\n", progname);
       exit(EXIT_FAILURE);
     }
 #else
     infile = stdin;
 #endif
   }

   /* Open the output file. */
 #ifdef TWO_FILE_COMMANDLINE
   /* Must have explicit output file name */
   if (argn != argc-2) {
     fprintf(stderr, "%s: must name one input and one output file\n",
             progname);
     usage();
   }
   if ((outfile = fopen(argv[argn+1], WRITE_BINARY)) == NULL) {
     fprintf(stderr, "%s: can't open %s\n", progname, argv[argn+1]);
     exit(EXIT_FAILURE);
   }
 #else
   /* Unix style: expect zero or one file name */
   if (argn < argc-1) {
     fprintf(stderr, "%s: only one input file\n", progname);
     usage();
   }
   /* default output file is stdout */
 #ifdef USE_SETMODE              /* need to hack file mode? */
   setmode(fileno(stdout), O_BINARY);
 #endif
 #ifdef USE_FDOPEN               /* need to re-open in binary mode? */
   if ((outfile = fdopen(fileno(stdout), WRITE_BINARY)) == NULL) {
     fprintf(stderr, "%s: can't open stdout\n", progname);
     exit(EXIT_FAILURE);
   }
 #else
   outfile = stdout;
 #endif
 #endif /* TWO_FILE_COMMANDLINE */

   /* Collect comment text from comment_file or stdin, if necessary */
   if (comment_arg == NULL) {
     FILE * src_file;
     int c;

     comment_arg = (char *) malloc((size_t) MAX_COM_LENGTH);
     if (comment_arg == NULL)
       ERREXIT("Insufficient memory");
     comment_length = 0;
     src_file = (comment_file != NULL ? comment_file : stdin);
     while ((c = getc(src_file)) != EOF) {
       if (comment_length >= (unsigned int) MAX_COM_LENGTH) {
         fprintf(stderr, "Comment text may not exceed %u bytes\n",
                 (unsigned int) MAX_COM_LENGTH);
         exit(EXIT_FAILURE);
       }
       comment_arg[comment_length++] = (char) c;
     }
     if (comment_file != NULL)
       fclose(comment_file);
   }

   /* Copy JPEG headers until SOFn marker;
    * we will insert the new comment marker just before SOFn.
    * This (a) causes the new comment to appear after, rather than before,
    * existing comments; and (b) ensures that comments come after any JFIF
    * or JFXX markers, as required by the JFIF specification.
    */
   marker = scan_JPEG_header(keep_COM);
   /* Insert the new COM marker, but only if nonempty text has been supplied */
   if (comment_length > 0) {
     write_marker(M_COM);
     write_2_bytes(comment_length + 2);
     while (comment_length > 0) {
       write_1_byte(*comment_arg++);
       comment_length--;
     }
   }
   /* Duplicate the remainder of the source file.
    * Note that any COM markers occuring after SOF will not be touched.
    */
   write_marker(marker);
   copy_rest_of_file();

   /* All done. */
   exit(EXIT_SUCCESS);
   return 0;                     /* suppress no-return-value warnings */
 }
	/*
	* wrjpgcom.c
	*
	* This file was part of the Independent JPEG Group's software:
	* Copyright (C) 1994-1997, Thomas G. Lane.
	* libjpeg-turbo Modifications:
	* Copyright (C) 2014, D. R. Commander
	* For conditions of distribution and use, see the accompanying README.ijg
	* file.
	*
	* This file contains a very simple stand-alone application that inserts
	* user-supplied text as a COM (comment) marker in a JFIF file.
	* This may be useful as an example of the minimum logic needed to parse
	* JPEG markers.
	*/

	#define JPEG_CJPEG_DJPEG /* to get the command-line config symbols */
	#include "jinclude.h" /* get auto-config symbols, <stdio.h> */

	#ifndef HAVE_STDLIB_H /* <stdlib.h> should declare malloc() */
	extern void * malloc ();
	#endif
	#include <ctype.h> /* to declare isupper(), tolower() */
	#ifdef USE_SETMODE
	#include <fcntl.h> /* to declare setmode()'s parameter macros */
	/* If you have setmode() but not <io.h>, just delete this line: */
	#include <io.h> /* to declare setmode() */
	#endif

	#ifdef USE_CCOMMAND /* command-line reader for Macintosh */
	#ifdef __MWERKS__
	#include <SIOUX.h> /* Metrowerks needs this */
	#include <console.h> /* ... and this */
	#endif
	#ifdef THINK_C
	#include <console.h> /* Think declares it here */
	#endif
	#endif

	#ifdef DONT_USE_B_MODE /* define mode parameters for fopen() */
	#define READ_BINARY "r"
	#define WRITE_BINARY "w"
	#else
	#define READ_BINARY "rb"
	#define WRITE_BINARY "wb"
	#endif

	#ifndef EXIT_FAILURE /* define exit() codes if not provided */
	#define EXIT_FAILURE 1
	#endif
	#ifndef EXIT_SUCCESS
	#define EXIT_SUCCESS 0
	#endif

	/* Reduce this value if your malloc() can't allocate blocks up to 64K.
	* On DOS, compiling in large model is usually a better solution.
	*/

	#ifndef MAX_COM_LENGTH
	#define MAX_COM_LENGTH 65000L /* must be <= 65533 in any case */
	#endif


	/*
	* These macros are used to read the input file and write the output file.
	* To reuse this code in another application, you might need to change these.
	*/

	static FILE * infile; /* input JPEG file */

	/* Return next input byte, or EOF if no more */
	#define NEXTBYTE() getc(infile)

	static FILE * outfile; /* output JPEG file */

	/* Emit an output byte */
	#define PUTBYTE(x) putc((x), outfile)


	/* Error exit handler */
	#define ERREXIT(msg) (fprintf(stderr, "%s\n", msg), exit(EXIT_FAILURE))


	/* Read one byte, testing for EOF */
	static int
	read_1_byte (void)
	{
	int c;

	c = NEXTBYTE();
	if (c == EOF)
	ERREXIT("Premature EOF in JPEG file");
	return c;
	}

	/* Read 2 bytes, convert to unsigned int */
	/* All 2-byte quantities in JPEG markers are MSB first */
	static unsigned int
	read_2_bytes (void)
	{
	int c1, c2;

	c1 = NEXTBYTE();
	if (c1 == EOF)
	ERREXIT("Premature EOF in JPEG file");
	c2 = NEXTBYTE();
	if (c2 == EOF)
	ERREXIT("Premature EOF in JPEG file");
	return (((unsigned int) c1) << 8) + ((unsigned int) c2);
	}


	/* Routines to write data to output file */

	static void
	write_1_byte (int c)
	{
	PUTBYTE(c);
	}

	static void
	write_2_bytes (unsigned int val)
	{
	PUTBYTE((val >> 8) & 0xFF);
	PUTBYTE(val & 0xFF);
	}

	static void
	write_marker (int marker)
	{
	PUTBYTE(0xFF);
	PUTBYTE(marker);
	}

	static void
	copy_rest_of_file (void)
	{
	int c;

	while ((c = NEXTBYTE()) != EOF)
	PUTBYTE(c);
	}


	/*
	* JPEG markers consist of one or more 0xFF bytes, followed by a marker
	* code byte (which is not an FF). Here are the marker codes of interest
	* in this program. (See jdmarker.c for a more complete list.)
	*/

	#define M_SOF0 0xC0 /* Start Of Frame N */
	#define M_SOF1 0xC1 /* N indicates which compression process */
	#define M_SOF2 0xC2 /* Only SOF0-SOF2 are now in common use */
	#define M_SOF3 0xC3
	#define M_SOF5 0xC5 /* NB: codes C4 and CC are NOT SOF markers */
	#define M_SOF6 0xC6
	#define M_SOF7 0xC7
	#define M_SOF9 0xC9
	#define M_SOF10 0xCA
	#define M_SOF11 0xCB
	#define M_SOF13 0xCD
	#define M_SOF14 0xCE
	#define M_SOF15 0xCF
	#define M_SOI 0xD8 /* Start Of Image (beginning of datastream) */
	#define M_EOI 0xD9 /* End Of Image (end of datastream) */
	#define M_SOS 0xDA /* Start Of Scan (begins compressed data) */
	#define M_COM 0xFE /* COMment */


	/*
	* Find the next JPEG marker and return its marker code.
	* We expect at least one FF byte, possibly more if the compressor used FFs
	* to pad the file. (Padding FFs will NOT be replicated in the output file.)
	* There could also be non-FF garbage between markers. The treatment of such
	* garbage is unspecified; we choose to skip over it but emit a warning msg.
	* NB: this routine must not be used after seeing SOS marker, since it will
	* not deal correctly with FF/00 sequences in the compressed image data...
	*/

	static int
	next_marker (void)
	{
	int c;
	int discarded_bytes = 0;

	/* Find 0xFF byte; count and skip any non-FFs. */
	c = read_1_byte();
	while (c != 0xFF) {
	discarded_bytes++;
	c = read_1_byte();
	}
	/* Get marker code byte, swallowing any duplicate FF bytes. Extra FFs
	* are legal as pad bytes, so don't count them in discarded_bytes.
	*/
	do {
	c = read_1_byte();
	} while (c == 0xFF);

	if (discarded_bytes != 0) {
	fprintf(stderr, "Warning: garbage data found in JPEG file\n");
	}

	return c;
	}


	/*
	* Read the initial marker, which should be SOI.
	* For a JFIF file, the first two bytes of the file should be literally
	* 0xFF M_SOI. To be more general, we could use next_marker, but if the
	* input file weren't actually JPEG at all, next_marker might read the whole
	* file and then return a misleading error message...
	*/

	static int
	first_marker (void)
	{
	int c1, c2;

	c1 = NEXTBYTE();
	c2 = NEXTBYTE();
	if (c1 != 0xFF \|\| c2 != M_SOI)
	ERREXIT("Not a JPEG file");
	return c2;
	}


	/*
	* Most types of marker are followed by a variable-length parameter segment.
	* This routine skips over the parameters for any marker we don't otherwise
	* want to process.
	* Note that we MUST skip the parameter segment explicitly in order not to
	* be fooled by 0xFF bytes that might appear within the parameter segment;
	* such bytes do NOT introduce new markers.
	*/

	static void
	copy_variable (void)
	/* Copy an unknown or uninteresting variable-length marker */
	{
	unsigned int length;

	/* Get the marker parameter length count */
	length = read_2_bytes();
	write_2_bytes(length);
	/* Length includes itself, so must be at least 2 */
	if (length < 2)
	ERREXIT("Erroneous JPEG marker length");
	length -= 2;
	/* Skip over the remaining bytes */
	while (length > 0) {
	write_1_byte(read_1_byte());
	length--;
	}
	}

	static void
	skip_variable (void)
	/* Skip over an unknown or uninteresting variable-length marker */
	{
	unsigned int length;

	/* Get the marker parameter length count */
	length = read_2_bytes();
	/* Length includes itself, so must be at least 2 */
	if (length < 2)
	ERREXIT("Erroneous JPEG marker length");
	length -= 2;
	/* Skip over the remaining bytes */
	while (length > 0) {
	(void) read_1_byte();
	length--;
	}
	}


	/*
	* Parse the marker stream until SOFn or EOI is seen;
	* copy data to output, but discard COM markers unless keep_COM is true.
	*/

	static int
	scan_JPEG_header (int keep_COM)
	{
	int marker;

	/* Expect SOI at start of file */
	if (first_marker() != M_SOI)
	ERREXIT("Expected SOI marker first");
	write_marker(M_SOI);

	/* Scan miscellaneous markers until we reach SOFn. */
	for (;;) {
	marker = next_marker();
	switch (marker) {
	/* Note that marker codes 0xC4, 0xC8, 0xCC are not, and must not be,
	* treated as SOFn. C4 in particular is actually DHT.
	*/
	case M_SOF0: /* Baseline */
	case M_SOF1: /* Extended sequential, Huffman */
	case M_SOF2: /* Progressive, Huffman */
	case M_SOF3: /* Lossless, Huffman */
	case M_SOF5: /* Differential sequential, Huffman */
	case M_SOF6: /* Differential progressive, Huffman */
	case M_SOF7: /* Differential lossless, Huffman */
	case M_SOF9: /* Extended sequential, arithmetic */
	case M_SOF10: /* Progressive, arithmetic */
	case M_SOF11: /* Lossless, arithmetic */
	case M_SOF13: /* Differential sequential, arithmetic */
	case M_SOF14: /* Differential progressive, arithmetic */
	case M_SOF15: /* Differential lossless, arithmetic */
	return marker;

	case M_SOS: /* should not see compressed data before SOF */
	ERREXIT("SOS without prior SOFn");
	break;

	case M_EOI: /* in case it's a tables-only JPEG stream */
	return marker;

	case M_COM: /* Existing COM: conditionally discard */
	if (keep_COM) {
	write_marker(marker);
	copy_variable();
	} else {
	skip_variable();
	}
	break;

	default: /* Anything else just gets copied */
	write_marker(marker);
	copy_variable(); /* we assume it has a parameter count... */
	break;
	}
	} /* end loop */
	}


	/* Command line parsing code */

	static const char * progname; /* program name for error messages */


	static void
	usage (void)
	/* complain about bad command line */
	{
	fprintf(stderr, "wrjpgcom inserts a textual comment in a JPEG file.\n");
	fprintf(stderr, "You can add to or replace any existing comment(s).\n");

	fprintf(stderr, "Usage: %s [switches] ", progname);
	#ifdef TWO_FILE_COMMANDLINE
	fprintf(stderr, "inputfile outputfile\n");
	#else
	fprintf(stderr, "[inputfile]\n");
	#endif

	fprintf(stderr, "Switches (names may be abbreviated):\n");
	fprintf(stderr, " -replace Delete any existing comments\n");
	fprintf(stderr, " -comment \"text\" Insert comment with given text\n");
	fprintf(stderr, " -cfile name Read comment from named file\n");
	fprintf(stderr, "Notice that you must put quotes around the comment text\n");
	fprintf(stderr, "when you use -comment.\n");
	fprintf(stderr, "If you do not give either -comment or -cfile on the command line,\n");
	fprintf(stderr, "then the comment text is read from standard input.\n");
	fprintf(stderr, "It can be multiple lines, up to %u characters total.\n",
	(unsigned int) MAX_COM_LENGTH);
	#ifndef TWO_FILE_COMMANDLINE
	fprintf(stderr, "You must specify an input JPEG file name when supplying\n");
	fprintf(stderr, "comment text from standard input.\n");
	#endif

	exit(EXIT_FAILURE);
	}


	static int
	keymatch (char * arg, const char * keyword, int minchars)
	/* Case-insensitive matching of (possibly abbreviated) keyword switches. */
	/* keyword is the constant keyword (must be lower case already), */
	/* minchars is length of minimum legal abbreviation. */
	{
	register int ca, ck;
	register int nmatched = 0;

	while ((ca = *arg++) != '\0') {
	if ((ck = *keyword++) == '\0')
	return 0; /* arg longer than keyword, no good */
	if (isupper(ca)) /* force arg to lcase (assume ck is already) */
	ca = tolower(ca);
	if (ca != ck)
	return 0; /* no good */
	nmatched++; /* count matched characters */
	}
	/* reached end of argument; fail if it's too short for unique abbrev */
	if (nmatched < minchars)
	return 0;
	return 1; /* A-OK */
	}


	/*
	* The main program.
	*/

	int
	main (int argc, char **argv)
	{
	int argn;
	char * arg;
	int keep_COM = 1;
	char * comment_arg = NULL;
	FILE * comment_file = NULL;
	unsigned int comment_length = 0;
	int marker;

	/* On Mac, fetch a command line. */
	#ifdef USE_CCOMMAND
	argc = ccommand(&argv);
	#endif

	progname = argv[0];
	if (progname == NULL \|\| progname[0] == 0)
	progname = "wrjpgcom"; /* in case C library doesn't provide it */

	/* Parse switches, if any */
	for (argn = 1; argn < argc; argn++) {
	arg = argv[argn];
	if (arg[0] != '-')
	break; /* not switch, must be file name */
	arg++; /* advance over '-' */
	if (keymatch(arg, "replace", 1)) {
	keep_COM = 0;
	} else if (keymatch(arg, "cfile", 2)) {
	if (++argn >= argc) usage();
	if ((comment_file = fopen(argv[argn], "r")) == NULL) {
	fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
	exit(EXIT_FAILURE);
	}
	} else if (keymatch(arg, "comment", 1)) {
	if (++argn >= argc) usage();
	comment_arg = argv[argn];
	/* If the comment text starts with '"', then we are probably running
	* under MS-DOG and must parse out the quoted string ourselves. Sigh.
	*/
	if (comment_arg[0] == '"') {
	comment_arg = (char *) malloc((size_t) MAX_COM_LENGTH);
	if (comment_arg == NULL)
	ERREXIT("Insufficient memory");
	if (strlen(argv[argn]) + 2 >= (size_t) MAX_COM_LENGTH) {
	fprintf(stderr, "Comment text may not exceed %u bytes\n",
	(unsigned int) MAX_COM_LENGTH);
	exit(EXIT_FAILURE);
	}
	strcpy(comment_arg, argv[argn]+1);
	for (;;) {
	comment_length = (unsigned int) strlen(comment_arg);
	if (comment_length > 0 && comment_arg[comment_length-1] == '"') {
	comment_arg[comment_length-1] = '\0'; /* zap terminating quote */
	break;
	}
	if (++argn >= argc)
	ERREXIT("Missing ending quote mark");
	if (strlen(comment_arg) + strlen(argv[argn]) + 2 >=
	(size_t) MAX_COM_LENGTH) {
	fprintf(stderr, "Comment text may not exceed %u bytes\n",
	(unsigned int) MAX_COM_LENGTH);
	exit(EXIT_FAILURE);
	}
	strcat(comment_arg, " ");
	strcat(comment_arg, argv[argn]);
	}
	} else if (strlen(argv[argn]) >= (size_t) MAX_COM_LENGTH) {
	fprintf(stderr, "Comment text may not exceed %u bytes\n",
	(unsigned int) MAX_COM_LENGTH);
	exit(EXIT_FAILURE);
	}
	comment_length = (unsigned int) strlen(comment_arg);
	} else
	usage();
	}

	/* Cannot use both -comment and -cfile. */
	if (comment_arg != NULL && comment_file != NULL)
	usage();
	/* If there is neither -comment nor -cfile, we will read the comment text
	* from stdin; in this case there MUST be an input JPEG file name.
	*/
	if (comment_arg == NULL && comment_file == NULL && argn >= argc)
	usage();

	/* Open the input file. */
	if (argn < argc) {
	if ((infile = fopen(argv[argn], READ_BINARY)) == NULL) {
	fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
	exit(EXIT_FAILURE);
	}
	} else {
	/* default input file is stdin */
	#ifdef USE_SETMODE /* need to hack file mode? */
	setmode(fileno(stdin), O_BINARY);
	#endif
	#ifdef USE_FDOPEN /* need to re-open in binary mode? */
	if ((infile = fdopen(fileno(stdin), READ_BINARY)) == NULL) {
	fprintf(stderr, "%s: can't open stdin\n", progname);
	exit(EXIT_FAILURE);
	}
	#else
	infile = stdin;
	#endif
	}

	/* Open the output file. */
	#ifdef TWO_FILE_COMMANDLINE
	/* Must have explicit output file name */
	if (argn != argc-2) {
	fprintf(stderr, "%s: must name one input and one output file\n",
	progname);
	usage();
	}
	if ((outfile = fopen(argv[argn+1], WRITE_BINARY)) == NULL) {
	fprintf(stderr, "%s: can't open %s\n", progname, argv[argn+1]);
	exit(EXIT_FAILURE);
	}
	#else
	/* Unix style: expect zero or one file name */
	if (argn < argc-1) {
	fprintf(stderr, "%s: only one input file\n", progname);
	usage();
	}
	/* default output file is stdout */
	#ifdef USE_SETMODE /* need to hack file mode? */
	setmode(fileno(stdout), O_BINARY);
	#endif
	#ifdef USE_FDOPEN /* need to re-open in binary mode? */
	if ((outfile = fdopen(fileno(stdout), WRITE_BINARY)) == NULL) {
	fprintf(stderr, "%s: can't open stdout\n", progname);
	exit(EXIT_FAILURE);
	}
	#else
	outfile = stdout;
	#endif
	#endif /* TWO_FILE_COMMANDLINE */

	/* Collect comment text from comment_file or stdin, if necessary */
	if (comment_arg == NULL) {
	FILE * src_file;
	int c;

	comment_arg = (char *) malloc((size_t) MAX_COM_LENGTH);
	if (comment_arg == NULL)
	ERREXIT("Insufficient memory");
	comment_length = 0;
	src_file = (comment_file != NULL ? comment_file : stdin);
	while ((c = getc(src_file)) != EOF) {
	if (comment_length >= (unsigned int) MAX_COM_LENGTH) {
	fprintf(stderr, "Comment text may not exceed %u bytes\n",
	(unsigned int) MAX_COM_LENGTH);
	exit(EXIT_FAILURE);
	}
	comment_arg[comment_length++] = (char) c;
	}
	if (comment_file != NULL)
	fclose(comment_file);
	}

	/* Copy JPEG headers until SOFn marker;
	* we will insert the new comment marker just before SOFn.
	* This (a) causes the new comment to appear after, rather than before,
	* existing comments; and (b) ensures that comments come after any JFIF
	* or JFXX markers, as required by the JFIF specification.
	*/
	marker = scan_JPEG_header(keep_COM);
	/* Insert the new COM marker, but only if nonempty text has been supplied */
	if (comment_length > 0) {
	write_marker(M_COM);
	write_2_bytes(comment_length + 2);
	while (comment_length > 0) {
	write_1_byte(*comment_arg++);
	comment_length--;
	}
	}
	/* Duplicate the remainder of the source file.
	* Note that any COM markers occuring after SOF will not be touched.
	*/
	write_marker(marker);
	copy_rest_of_file();

	/* All done. */
	exit(EXIT_SUCCESS);
	return 0; /* suppress no-return-value warnings */
	}