JPEGView/Independent JPEG Group/jmorecfg.h

/*
 * jmorecfg.h
 *
 * Copyright (C) 1991-1994, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains additional configuration options that customize the
 * JPEG software for special applications or support machine-dependent
 * optimizations.  Most users will not need to touch this file.
 */


/*
 * Define BITS_IN_JSAMPLE as either
 *   8   for 8-bit sample values (the usual setting)
 *   12  for 12-bit sample values
 * Only 8 and 12 are legal data precisions for lossy JPEG according to the
 * JPEG standard, and the IJG code does not support anything else!
 * We do not support run-time selection of data precision, sorry.
 */

#define BITS_IN_JSAMPLE  8	/* use 8 or 12 */


/*
 * Maximum number of components (color channels) allowed in JPEG image.
 * To meet the letter of the JPEG spec, set this to 255.  However, darn
 * few applications need more than 4 channels (maybe 5 for CMYK + alpha
 * mask).  We recommend 10 as a reasonable compromise; use 4 if you are
 * really short on memory.  (Each allowed component costs a hundred or so
 * bytes of storage, whether actually used in an image or not.)
 */

#define MAX_COMPONENTS  10	/* maximum number of image components */


/*
 * Basic data types.
 * You may need to change these if you have a machine with unusual data
 * type sizes; for example, "char" not 8 bits, "short" not 16 bits,
 * or "long" not 32 bits.  We don't care whether "int" is 16 or 32 bits,
 * but it had better be at least 16.
 */

/* Representation of a single sample (pixel element value).
 * We frequently allocate large arrays of these, so it's important to keep
 * them small.  But if you have memory to burn and access to char or short
 * arrays is very slow on your hardware, you might want to change these.
 */

#if BITS_IN_JSAMPLE == 8
/* JSAMPLE should be the smallest type that will hold the values 0..255.
 * You can use a signed char by having GETJSAMPLE mask it with 0xFF.
 */

#ifdef HAVE_UNSIGNED_CHAR

typedef unsigned char JSAMPLE;
#define GETJSAMPLE(value)  (value)

#else /* not HAVE_UNSIGNED_CHAR */

typedef char JSAMPLE;
#ifdef CHAR_IS_UNSIGNED
#define GETJSAMPLE(value)  (value)
#else
#define GETJSAMPLE(value)  ((value) & 0xFF)
#endif /* CHAR_IS_UNSIGNED */

#endif /* HAVE_UNSIGNED_CHAR */

#define MAXJSAMPLE	255
#define CENTERJSAMPLE	128

#endif /* BITS_IN_JSAMPLE == 8 */


#if BITS_IN_JSAMPLE == 12
/* JSAMPLE should be the smallest type that will hold the values 0..4095.
 * On nearly all machines "short" will do nicely.
 */

typedef short JSAMPLE;
#define GETJSAMPLE(value)  (value)

#define MAXJSAMPLE	4095
#define CENTERJSAMPLE	2048

#endif /* BITS_IN_JSAMPLE == 12 */


/* Representation of a DCT frequency coefficient.
 * This should be a signed value of at least 16 bits; "short" is usually OK.
 * Again, we allocate large arrays of these, but you can change to int
 * if you have memory to burn and "short" is really slow.
 */

typedef short JCOEF;


/* Compressed datastreams are represented as arrays of JOCTET.
 * These must be EXACTLY 8 bits wide, at least once they are written to
 * external storage.  Note that when using the stdio data source/destination
 * managers, this is also the data type passed to fread/fwrite.
 */

#ifdef HAVE_UNSIGNED_CHAR

typedef unsigned char JOCTET;
#define GETJOCTET(value)  (value)

#else /* not HAVE_UNSIGNED_CHAR */

typedef char JOCTET;
#ifdef CHAR_IS_UNSIGNED
#define GETJOCTET(value)  (value)
#else
#define GETJOCTET(value)  ((value) & 0xFF)
#endif /* CHAR_IS_UNSIGNED */

#endif /* HAVE_UNSIGNED_CHAR */


/* These typedefs are used for various table entries and so forth.
 * They must be at least as wide as specified; but making them too big
 * won't cost a huge amount of memory, so we don't provide special
 * extraction code like we did for JSAMPLE.  (In other words, these
 * typedefs live at a different point on the speed/space tradeoff curve.)
 */

/* UINT8 must hold at least the values 0..255. */

#ifdef HAVE_UNSIGNED_CHAR
typedef unsigne