png.c

/* png.c - location for general purpose png functions

   libpng 1.0 beta 4 - version 0.90
   For conditions of distribution and use, see copyright notice in png.h
   Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
   January 10, 1997
   */

#define PNG_INTERNAL
#define PNG_NO_EXTERN
#include "png.h"

/* version information for c files.  This better match the version
   string defined in png.h */
char png_libpng_ver[] = "0.90";

/* place to hold the signiture string for a png file. */
png_byte FARDATA png_sig[8] = {137, 80, 78, 71, 13, 10, 26, 10};

/* constant strings for known chunk types.  If you need to add a chunk,
   add a string holding the name here.  If you want to make the code
   portable to EBCDIC machines, use ASCII numbers, not characters. */
png_byte FARDATA png_IHDR[4] = { 73,  72,  68,  82};
png_byte FARDATA png_IDAT[4] = { 73,  68,  65,  84};
png_byte FARDATA png_IEND[4] = { 73,  69,  78,  68};
png_byte FARDATA png_PLTE[4] = { 80,  76,  84,  69};
png_byte FARDATA png_gAMA[4] = {103,  65,  77,  65};
png_byte FARDATA png_sBIT[4] = {115,  66,  73,  84};
png_byte FARDATA png_cHRM[4] = { 99,  72,  82,  77};
png_byte FARDATA png_tRNS[4] = {116,  82,  78,  83};
png_byte FARDATA png_bKGD[4] = { 98,  75,  71,  68};
png_byte FARDATA png_hIST[4] = {104,  73,  83,  84};
png_byte FARDATA png_tEXt[4] = {116,  69,  88, 116};
png_byte FARDATA png_zTXt[4] = {122,  84,  88, 116};
png_byte FARDATA png_pHYs[4] = {112,  72,  89, 115};
png_byte FARDATA png_oFFs[4] = {111,  70,  70, 115};
png_byte FARDATA png_tIME[4] = {116,  73,  77,  69};

/* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

/* start of interlace block */
int FARDATA png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};

/* offset to next interlace block */
int FARDATA png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};

/* start of interlace block in the y direction */
int FARDATA png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};

/* offset to next interlace block in the y direction */
int FARDATA png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};

/* width of interlace block */
/* this is not currently used - if you need it, uncomment it here and
   in png.h
int FARDATA png_pass_width[] = {8, 4, 4, 2, 2, 1, 1};
*/

/* height of interlace block */
/* this is not currently used - if you need it, uncomment it here and
   in png.h
int FARDATA png_pass_height[] = {8, 8, 4, 4, 2, 2, 1};
*/

/* mask to determine which pixels are valid in a pass */
int FARDATA png_pass_mask[] = {0x80, 0x08, 0x88, 0x22, 0xaa, 0x55, 0xff};

/* mask to determine which pixels to overwrite while displaying */
int FARDATA png_pass_dsp_mask[] = {0xff, 0x0f, 0xff, 0x33, 0xff, 0x55, 0xff};


/* Tells libpng that we have already handled the first "num_bytes" bytes
 * of the PNG file signature.  If the PNG data is embedded into another
 * stream we can set num_bytes = 8 so that libpng will not attempt to read
 * or write any of the magic bytes before it starts on the IHDR.
 */
void
png_set_sig_bytes(png_structp png_ptr, int num_bytes)
{
   if (num_bytes > 8)
      png_error(png_ptr, "Too many bytes for PNG signature.");

   png_ptr->sig_bytes = num_bytes < 0 ? 0 : num_bytes;
}

/* Checks whether the supplied bytes match the PNG signature.  We allow
 * checking less than the full 8-byte signature so that those apps that
 * already read the first few bytes of a file to determine the file type
 * can simply check the remaining bytes for extra assurance.  Returns
 * an integer less than, equal to, or greater than zero if sig is found,
 * respectively, to be less than, to match, or be greater than the correct
 * PNG signature (this is the same behaviour as strcmp, memcmp, etc).
 */
int
png_sig_cmp(png_bytep sig, int start, int num_to_check)
{
   if (num_to_check > 8)
      num_to_check = 8;
   else if (num_to_check < 1)
      return 0;

   if (start > 7 || start < 0)
      return 0;

   if (start + num_to_check > 8)
      num_to_check = 8 - start;

   return (png_memcmp(sig, &png_sig[start], (unsigned int)num_to_check));
}

/* (Obsolete) function to check signature bytes.  It does not allow one
   to check a partial signature.  This function will be removed in the
   future - use png_sig_cmp(). */
int
png_check_sig(png_bytep sig, int num)
{
  return !png_sig_cmp(sig, 0, num);
}

/* Function to allocate memory for zlib. */
voidpf
png_zalloc(voidpf png_ptr, uInt items, uInt size)
{
   png_voidp ptr;
   png_uint_32 num_bytes;

   ptr = png_malloc((png_structp)png_ptr,
      (png_uint_32)items * (png_uint_32)size);
   num_bytes = (png_uint_32)items * (png_uint_32)size;
   if (num_bytes > (png_uint_32)0x7fff)
   {
      png_memset(ptr, 0, (png_size_t)0x8000L);
      png_memset((png_bytep)ptr + (png_size_t)0x8000L, 0,
         (png_size_t)(num_bytes - (png_uint_32)0x8000L));
   }
   else
   {
      png_memset(ptr, 0, (png_size_t)num_bytes);
   }
   return (voidpf)(ptr);
}

/* function to free memory for zlib */
void
png_zfree(voidpf png_ptr, voidpf ptr)
{
   png_free((png_structp)png_ptr, (png_voidp)ptr);
}

/* Reset the CRC variable to 32 bits of 1's.  Care must be taken
   in case CRC is > 32 bits to leave the top bits 0. */
void
png_reset_crc(png_structp png_ptr)
{
   /* set crc to all 1's */
#ifdef PNG_USE_OWN_CRC
   png_ptr->crc = 0xffffffffL;
#else
   png_ptr->crc = crc32(0, Z_NULL, 0);
#endif
}

#ifdef PNG_USE_OWN_CRC
/* Table of CRC's of all 8-bit messages.  If you wish to png_malloc this
   table, turn this into a pointer, and png_malloc() it in make_crc_table().
   You may then want to hook it into png_struct and free it with the
   destroy functions.  Another alternative is to pre-fill the table.  */
static png_uint_32 crc_table[256];

/* Flag: has the table been computed? Initially false. */
static int crc_table_computed = 0;

/* make the table for a fast crc */
static void
make_crc_table(void)
{
  png_uint_32 c;
  int n, k;

  for (n = 0; n < 256; n++)
  {
   c = (png_uint_32)n;
   for (k = 0; k < 8; k++)
     c = c & 1 ? 0xedb88320L ^ (c >> 1) : c >> 1;
   crc_table[n] = c;
  }
  crc_table_computed = 1;
}

/* Update a running CRC with the bytes buf[0..len-1]--the crc should be
   initialized to all 1's, and the transmitted value is the 1's complement
   of the final running CRC. */
static png_uint_32
update_crc(png_uint_32 crc, png_bytep buf, png_uint_32 len)
{
  png_uint_32 c;
  png_bytep p;
  png_uint_32 n;

  c = crc;
  p = buf;
  n = len;

  if (!crc_table_computed)
  {
   make_crc_table();
  }

  if (n > 0) do
  {
   c = crc_table[(png_byte)((c ^ (*p++)) & 0xff)] ^ (c >> 8);
  } while (--n);

  return c;
}
#endif /* PNG_USE_OWN_CRC */

/* Calculate the crc over a section of data.  Note that while we
   are passing in a 32 bit value for length, on 16 bit machines, you
   would need to use huge pointers to access all that data.  If you
   need this, put huge here and above. */
void
png_calculate_crc(png_structp png_ptr, png_bytep ptr,
   png_uint_32 length)
{
#ifdef PNG_USE_OWN_CRC
   png_ptr->crc = update_crc(png_ptr->crc, ptr, length);
#else
   png_ptr->crc = crc32(png_ptr->crc, ptr, length);
#endif
}

/* Allocate the memory for an info_struct for the application.  We don't
   really need the png_ptr, but it could potentially be useful in the
   future.  This should be used in favour of malloc(sizeof(png_info))
   and png_info_init() so that applications that want to use a shared
   libpng don't have to be recompiled if png_info changes size. */
png_infop
png_create_info_struct(png_structp png_ptr)
{
   png_infop info_ptr;

   if ((info_ptr = (png_infop)png_create_struct(PNG_STRUCT_INFO)) != NULL)
   {
      png_info_init(info_ptr);
   }

   return info_ptr;
}

/* This function frees the memory associated with a single info struct.
   Normally, one would use either png_destroy_read_struct() or 
   png_destroy_write_struct() to free an info struct, but this may be
   useful for some applications. */
void
png_destroy_info_struct(png_structp png_ptr, png_infopp info_ptr_ptr)
{
   png_infop info_ptr = NULL;

   if (info_ptr_ptr)
      info_ptr = *info_ptr_ptr;

   if (info_ptr)
   {
      png_info_destroy(png_ptr, info_ptr);

      png_destroy_struct((png_voidp)info_ptr);
      *info_ptr_ptr = (png_infop)NULL;
   }
}

/* Initialize the info structure.  This is now an internal function (0.89)
   and applications using it are urged to use png_create_info_struct()
   instead. */
void
png_info_init(png_infop info_ptr)
{
   /* set everything to 0 */
   png_memset(info_ptr, 0, sizeof (png_info));
}

/* This is an internal routine to free any memory that the info struct is
   pointing to before re-using it or freeing the struct itself. */
void
png_info_destroy(png_structp png_ptr, png_infop info_ptr)
{
#if defined(PNG_READ_tEXt_SUPPORTED) || defined(PNG_READ_zTXt_SUPPORTED)
   int i;

   for (i = 0; i < info_ptr->num_text; i++)
   {
      png_free(png_ptr, info_ptr->text[i].key);
   }

   png_free(png_ptr, info_ptr->text);
#endif

   png_info_init(info_ptr);
}

/* This function returns a pointer to the io_ptr associated with the user
   functions.  The application should free any memory associated with this
   pointer before png_write_destroy() or png_read_destroy() are called. */
png_voidp
png_get_io_ptr(png_structp png_ptr)
{
   return png_ptr->io_ptr;
}
 
/* Initialize the default input/output functions for the png file.  If you
   change the read, or write routines, you can call either png_set_read_fn()
   or png_set_write_fn() instead of png_init_io(). */
void
png_init_io(png_structp png_ptr, FILE *fp)
{
   png_ptr->io_ptr = (png_voidp)fp;
}