kc3-lang/libpng/pngerror.c

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• Hash : 2a4f0f5a
  Author :
  Date : 2024-01-17T18:06:47
  

  De-volatilize the internal implementation of `png_safe_execute`
  
  `png_safe_execute` called `setjmp` in a context where the result was
  undefined (an assignment statement). This corrects the code and removes
  volatile statements that were introduced previously to quell warnings
  from earlier versions of GCC.
  
  Co-authored-by: John Bowler <jbowler@acm.org>
  

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• pngerror.c

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  /* pngerror.c - stub functions for i/o and memory allocation
   *
   * Copyright (c) 2018 Cosmin Truta
   * Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson
   * Copyright (c) 1996-1997 Andreas Dilger
   * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
   *
   * This code is released under the libpng license.
   * For conditions of distribution and use, see the disclaimer
   * and license in png.h
   *
   * This file provides a location for all error handling.  Users who
   * need special error handling are expected to write replacement functions
   * and use png_set_error_fn() to use those functions.  See the instructions
   * at each function.
   */
  
  #include "pngpriv.h"
  
  #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
  
  static PNG_FUNCTION(void, png_default_error,PNGARG((png_const_structrp png_ptr,
      png_const_charp error_message)),PNG_NORETURN);
  
  #ifdef PNG_WARNINGS_SUPPORTED
  static void /* PRIVATE */
  png_default_warning PNGARG((png_const_structrp png_ptr,
      png_const_charp warning_message));
  #endif /* WARNINGS */
  
  /* This function is called whenever there is a fatal error.  This function
   * should not be changed.  If there is a need to handle errors differently,
   * you should supply a replacement error function and use png_set_error_fn()
   * to replace the error function at run-time.
   */
  #ifdef PNG_ERROR_TEXT_SUPPORTED
  PNG_FUNCTION(void,PNGAPI
  png_error,(png_const_structrp png_ptr, png_const_charp error_message),
      PNG_NORETURN)
  {
  #ifdef PNG_ERROR_NUMBERS_SUPPORTED
     char msg[16];
     if (png_ptr != NULL)
     {
        if ((png_ptr->flags &
           (PNG_FLAG_STRIP_ERROR_NUMBERS|PNG_FLAG_STRIP_ERROR_TEXT)) != 0)
        {
           if (*error_message == PNG_LITERAL_SHARP)
           {
              /* Strip "#nnnn " from beginning of error message. */
              int offset;
              for (offset = 1; offset<15; offset++)
                 if (error_message[offset] == ' ')
                    break;
  
              if ((png_ptr->flags & PNG_FLAG_STRIP_ERROR_TEXT) != 0)
              {
                 int i;
                 for (i = 0; i < offset - 1; i++)
                    msg[i] = error_message[i + 1];
                 msg[i - 1] = '\0';
                 error_message = msg;
              }
  
              else
                 error_message += offset;
           }
  
           else
           {
              if ((png_ptr->flags & PNG_FLAG_STRIP_ERROR_TEXT) != 0)
              {
                 msg[0] = '0';
                 msg[1] = '\0';
                 error_message = msg;
              }
           }
        }
     }
  #endif
     if (png_ptr != NULL && png_ptr->error_fn != NULL)
        (*(png_ptr->error_fn))(png_constcast(png_structrp,png_ptr),
            error_message);
  
     /* If the custom handler doesn't exist, or if it returns,
        use the default handler, which will not return. */
     png_default_error(png_ptr, error_message);
  }
  #else
  PNG_FUNCTION(void,PNGAPI
  png_err,(png_const_structrp png_ptr),PNG_NORETURN)
  {
     /* Prior to 1.5.2 the error_fn received a NULL pointer, expressed
      * erroneously as '\0', instead of the empty string "".  This was
      * apparently an error, introduced in libpng-1.2.20, and png_default_error
      * will crash in this case.
      */
     if (png_ptr != NULL && png_ptr->error_fn != NULL)
        (*(png_ptr->error_fn))(png_constcast(png_structrp,png_ptr), "");
  
     /* If the custom handler doesn't exist, or if it returns,
        use the default handler, which will not return. */
     png_default_error(png_ptr, "");
  }
  #endif /* ERROR_TEXT */
  
  /* Utility to safely appends strings to a buffer.  This never errors out so
   * error checking is not required in the caller.
   */
  size_t
  png_safecat(png_charp buffer, size_t bufsize, size_t pos,
      png_const_charp string)
  {
     if (buffer != NULL && pos < bufsize)
     {
        if (string != NULL)
           while (*string != '\0' && pos < bufsize-1)
             buffer[pos++] = *string++;
  
        buffer[pos] = '\0';
     }
  
     return pos;
  }
  
  #if defined(PNG_WARNINGS_SUPPORTED) || defined(PNG_TIME_RFC1123_SUPPORTED)
  /* Utility to dump an unsigned value into a buffer, given a start pointer and
   * and end pointer (which should point just *beyond* the end of the buffer!)
   * Returns the pointer to the start of the formatted string.
   */
  png_charp
  png_format_number(png_const_charp start, png_charp end, int format,
      png_alloc_size_t number)
  {
     int count = 0;    /* number of digits output */
     int mincount = 1; /* minimum number required */
     int output = 0;   /* digit output (for the fixed point format) */
  
     *--end = '\0';
  
     /* This is written so that the loop always runs at least once, even with
      * number zero.
      */
     while (end > start && (number != 0 || count < mincount))
     {
  
        static const char digits[] = "0123456789ABCDEF";
  
        switch (format)
        {
           case PNG_NUMBER_FORMAT_fixed:
              /* Needs five digits (the fraction) */
              mincount = 5;
              if (output != 0 || number % 10 != 0)
              {
                 *--end = digits[number % 10];
                 output = 1;
              }
              number /= 10;
              break;
  
           case PNG_NUMBER_FORMAT_02u:
              /* Expects at least 2 digits. */
              mincount = 2;
              /* FALLTHROUGH */
  
           case PNG_NUMBER_FORMAT_u:
              *--end = digits[number % 10];
              number /= 10;
              break;
  
           case PNG_NUMBER_FORMAT_02x:
              /* This format expects at least two digits */
              mincount = 2;
              /* FALLTHROUGH */
  
           case PNG_NUMBER_FORMAT_x:
              *--end = digits[number & 0xf];
              number >>= 4;
              break;
  
           default: /* an error */
              number = 0;
              break;
        }
  
        /* Keep track of the number of digits added */
        ++count;
  
        /* Float a fixed number here: */
        if ((format == PNG_NUMBER_FORMAT_fixed) && (count == 5) && (end > start))
        {
           /* End of the fraction, but maybe nothing was output?  In that case
            * drop the decimal point.  If the number is a true zero handle that
            * here.
            */
           if (output != 0)
              *--end = '.';
           else if (number == 0) /* and !output */
              *--end = '0';
        }
     }
  
     return end;
  }
  #endif
  
  #ifdef PNG_WARNINGS_SUPPORTED
  /* This function is called whenever there is a non-fatal error.  This function
   * should not be changed.  If there is a need to handle warnings differently,
   * you should supply a replacement warning function and use
   * png_set_error_fn() to replace the warning function at run-time.
   */
  void PNGAPI
  png_warning(png_const_structrp png_ptr, png_const_charp warning_message)
  {
     int offset = 0;
     if (png_ptr != NULL)
     {
  #ifdef PNG_ERROR_NUMBERS_SUPPORTED
     if ((png_ptr->flags &
         (PNG_FLAG_STRIP_ERROR_NUMBERS|PNG_FLAG_STRIP_ERROR_TEXT)) != 0)
  #endif
        {
           if (*warning_message == PNG_LITERAL_SHARP)
           {
              for (offset = 1; offset < 15; offset++)
                 if (warning_message[offset] == ' ')
                    break;
           }
        }
     }
     if (png_ptr != NULL && png_ptr->warning_fn != NULL)
        (*(png_ptr->warning_fn))(png_constcast(png_structrp,png_ptr),
            warning_message + offset);
     else
        png_default_warning(png_ptr, warning_message + offset);
  }
  
  /* These functions support 'formatted' warning messages with up to
   * PNG_WARNING_PARAMETER_COUNT parameters.  In the format string the parameter
   * is introduced by @<number>, where 'number' starts at 1.  This follows the
   * standard established by X/Open for internationalizable error messages.
   */
  void
  png_warning_parameter(png_warning_parameters p, int number,
      png_const_charp string)
  {
     if (number > 0 && number <= PNG_WARNING_PARAMETER_COUNT)
        (void)png_safecat(p[number-1], (sizeof p[number-1]), 0, string);
  }
  
  void
  png_warning_parameter_unsigned(png_warning_parameters p, int number, int format,
      png_alloc_size_t value)
  {
     char buffer[PNG_NUMBER_BUFFER_SIZE] = {0};
     png_warning_parameter(p, number, PNG_FORMAT_NUMBER(buffer, format, value));
  }
  
  void
  png_warning_parameter_signed(png_warning_parameters p, int number, int format,
      png_int_32 value)
  {
     png_alloc_size_t u;
     png_charp str;
     char buffer[PNG_NUMBER_BUFFER_SIZE] = {0};
  
     /* Avoid overflow by doing the negate in a png_alloc_size_t: */
     u = (png_alloc_size_t)value;
     if (value < 0)
        u = ~u + 1;
  
     str = PNG_FORMAT_NUMBER(buffer, format, u);
  
     if (value < 0 && str > buffer)
        *--str = '-';
  
     png_warning_parameter(p, number, str);
  }
  
  void
  png_formatted_warning(png_const_structrp png_ptr, png_warning_parameters p,
      png_const_charp message)
  {
     /* The internal buffer is just 192 bytes - enough for all our messages,
      * overflow doesn't happen because this code checks!  If someone figures
      * out how to send us a message longer than 192 bytes, all that will
      * happen is that the message will be truncated appropriately.
      */
     size_t i = 0; /* Index in the msg[] buffer: */
     char msg[192];
  
     /* Each iteration through the following loop writes at most one character
      * to msg[i++] then returns here to validate that there is still space for
      * the trailing '\0'.  It may (in the case of a parameter) read more than
      * one character from message[]; it must check for '\0' and continue to the
      * test if it finds the end of string.
      */
     while (i<(sizeof msg)-1 && *message != '\0')
     {
        /* '@' at end of string is now just printed (previously it was skipped);
         * it is an error in the calling code to terminate the string with @.
         */
        if (p != NULL && *message == '@' && message[1] != '\0')
        {
           int parameter_char = *++message; /* Consume the '@' */
           static const char valid_parameters[] = "123456789";
           int parameter = 0;
  
           /* Search for the parameter digit, the index in the string is the
            * parameter to use.
            */
           while (valid_parameters[parameter] != parameter_char &&
              valid_parameters[parameter] != '\0')
              ++parameter;
  
           /* If the parameter digit is out of range it will just get printed. */
           if (parameter < PNG_WARNING_PARAMETER_COUNT)
           {
              /* Append this parameter */
              png_const_charp parm = p[parameter];
              png_const_charp pend = p[parameter] + (sizeof p[parameter]);
  
              /* No need to copy the trailing '\0' here, but there is no guarantee
               * that parm[] has been initialized, so there is no guarantee of a
               * trailing '\0':
               */
              while (i<(sizeof msg)-1 && *parm != '\0' && parm < pend)
                 msg[i++] = *parm++;
  
              /* Consume the parameter digit too: */
              ++message;
              continue;
           }
  
           /* else not a parameter and there is a character after the @ sign; just
            * copy that.  This is known not to be '\0' because of the test above.
            */
        }
  
        /* At this point *message can't be '\0', even in the bad parameter case
         * above where there is a lone '@' at the end of the message string.
         */
        msg[i++] = *message++;
     }
  
     /* i is always less than (sizeof msg), so: */
     msg[i] = '\0';
  
     /* And this is the formatted message. It may be larger than
      * PNG_MAX_ERROR_TEXT, but that is only used for 'chunk' errors and these
      * are not (currently) formatted.
      */
     png_warning(png_ptr, msg);
  }
  #endif /* WARNINGS */
  
  #ifdef PNG_BENIGN_ERRORS_SUPPORTED
  void PNGAPI
  png_benign_error(png_const_structrp png_ptr, png_const_charp error_message)
  {
     if ((png_ptr->flags & PNG_FLAG_BENIGN_ERRORS_WARN) != 0)
     {
  #     ifdef PNG_READ_SUPPORTED
           if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
              png_ptr->chunk_name != 0)
              png_chunk_warning(png_ptr, error_message);
           else
  #     endif
        png_warning(png_ptr, error_message);
     }
  
     else
     {
  #     ifdef PNG_READ_SUPPORTED
           if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
              png_ptr->chunk_name != 0)
              png_chunk_error(png_ptr, error_message);
           else
  #     endif
        png_error(png_ptr, error_message);
     }
  
  #  ifndef PNG_ERROR_TEXT_SUPPORTED
        PNG_UNUSED(error_message)
  #  endif
  }
  
  void /* PRIVATE */
  png_app_warning(png_const_structrp png_ptr, png_const_charp error_message)
  {
     if ((png_ptr->flags & PNG_FLAG_APP_WARNINGS_WARN) != 0)
        png_warning(png_ptr, error_message);
     else
        png_error(png_ptr, error_message);
  
  #  ifndef PNG_ERROR_TEXT_SUPPORTED
        PNG_UNUSED(error_message)
  #  endif
  }
  
  void /* PRIVATE */
  png_app_error(png_const_structrp png_ptr, png_const_charp error_message)
  {
     if ((png_ptr->flags & PNG_FLAG_APP_ERRORS_WARN) != 0)
        png_warning(png_ptr, error_message);
     else
        png_error(png_ptr, error_message);
  
  #  ifndef PNG_ERROR_TEXT_SUPPORTED
        PNG_UNUSED(error_message)
  #  endif
  }
  #endif /* BENIGN_ERRORS */
  
  #define PNG_MAX_ERROR_TEXT 196 /* Currently limited by profile_error in png.c */
  #if defined(PNG_WARNINGS_SUPPORTED) || \
     (defined(PNG_READ_SUPPORTED) && defined(PNG_ERROR_TEXT_SUPPORTED))
  /* These utilities are used internally to build an error message that relates
   * to the current chunk.  The chunk name comes from png_ptr->chunk_name,
   * which is used to prefix the message.  The message is limited in length
   * to 63 bytes. The name characters are output as hex digits wrapped in []
   * if the character is invalid.
   */
  #define isnonalpha(c) ((c) < 65 || (c) > 122 || ((c) > 90 && (c) < 97))
  static const char png_digit[16] = {
     '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
     'A', 'B', 'C', 'D', 'E', 'F'
  };
  
  static void /* PRIVATE */
  png_format_buffer(png_const_structrp png_ptr, png_charp buffer, png_const_charp
      error_message)
  {
     png_uint_32 chunk_name = png_ptr->chunk_name;
     int iout = 0, ishift = 24;
  
     while (ishift >= 0)
     {
        int c = (int)(chunk_name >> ishift) & 0xff;
  
        ishift -= 8;
        if (isnonalpha(c) != 0)
        {
           buffer[iout++] = PNG_LITERAL_LEFT_SQUARE_BRACKET;
           buffer[iout++] = png_digit[(c & 0xf0) >> 4];
           buffer[iout++] = png_digit[c & 0x0f];
           buffer[iout++] = PNG_LITERAL_RIGHT_SQUARE_BRACKET;
        }
  
        else
        {
           buffer[iout++] = (char)c;
        }
     }
  
     if (error_message == NULL)
        buffer[iout] = '\0';
  
     else
     {
        int iin = 0;
  
        buffer[iout++] = ':';
        buffer[iout++] = ' ';
  
        while (iin < PNG_MAX_ERROR_TEXT-1 && error_message[iin] != '\0')
           buffer[iout++] = error_message[iin++];
  
        /* iin < PNG_MAX_ERROR_TEXT, so the following is safe: */
        buffer[iout] = '\0';
     }
  }
  #endif /* WARNINGS || ERROR_TEXT */
  
  #if defined(PNG_READ_SUPPORTED) && defined(PNG_ERROR_TEXT_SUPPORTED)
  PNG_FUNCTION(void,PNGAPI
  png_chunk_error,(png_const_structrp png_ptr, png_const_charp error_message),
      PNG_NORETURN)
  {
     char msg[18+PNG_MAX_ERROR_TEXT];
     if (png_ptr == NULL)
        png_error(png_ptr, error_message);
  
     else
     {
        png_format_buffer(png_ptr, msg, error_message);
        png_error(png_ptr, msg);
     }
  }
  #endif /* READ && ERROR_TEXT */
  
  #ifdef PNG_WARNINGS_SUPPORTED
  void PNGAPI
  png_chunk_warning(png_const_structrp png_ptr, png_const_charp warning_message)
  {
     char msg[18+PNG_MAX_ERROR_TEXT];
     if (png_ptr == NULL)
        png_warning(png_ptr, warning_message);
  
     else
     {
        png_format_buffer(png_ptr, msg, warning_message);
        png_warning(png_ptr, msg);
     }
  }
  #endif /* WARNINGS */
  
  #ifdef PNG_READ_SUPPORTED
  #ifdef PNG_BENIGN_ERRORS_SUPPORTED
  void PNGAPI
  png_chunk_benign_error(png_const_structrp png_ptr, png_const_charp
      error_message)
  {
     if ((png_ptr->flags & PNG_FLAG_BENIGN_ERRORS_WARN) != 0)
        png_chunk_warning(png_ptr, error_message);
  
     else
        png_chunk_error(png_ptr, error_message);
  
  #  ifndef PNG_ERROR_TEXT_SUPPORTED
        PNG_UNUSED(error_message)
  #  endif
  }
  #endif
  #endif /* READ */
  
  void /* PRIVATE */
  png_chunk_report(png_const_structrp png_ptr, png_const_charp message, int error)
  {
  #  ifndef PNG_WARNINGS_SUPPORTED
        PNG_UNUSED(message)
  #  endif
  
     /* This is always supported, but for just read or just write it
      * unconditionally does the right thing.
      */
  #  if defined(PNG_READ_SUPPORTED) && defined(PNG_WRITE_SUPPORTED)
        if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0)
  #  endif
  
  #  ifdef PNG_READ_SUPPORTED
        {
           if (error < PNG_CHUNK_ERROR)
              png_chunk_warning(png_ptr, message);
  
           else
              png_chunk_benign_error(png_ptr, message);
        }
  #  endif
  
  #  if defined(PNG_READ_SUPPORTED) && defined(PNG_WRITE_SUPPORTED)
        else if ((png_ptr->mode & PNG_IS_READ_STRUCT) == 0)
  #  endif
  
  #  ifdef PNG_WRITE_SUPPORTED
        {
           if (error < PNG_CHUNK_WRITE_ERROR)
              png_app_warning(png_ptr, message);
  
           else
              png_app_error(png_ptr, message);
        }
  #  endif
  }
  
  #ifdef PNG_ERROR_TEXT_SUPPORTED
  #ifdef PNG_FLOATING_POINT_SUPPORTED
  PNG_FUNCTION(void,
  png_fixed_error,(png_const_structrp png_ptr, png_const_charp name),PNG_NORETURN)
  {
  #  define fixed_message "fixed point overflow in "
  #  define fixed_message_ln ((sizeof fixed_message)-1)
     unsigned int  iin;
     char msg[fixed_message_ln+PNG_MAX_ERROR_TEXT];
     memcpy(msg, fixed_message, fixed_message_ln);
     iin = 0;
     if (name != NULL)
        while (iin < (PNG_MAX_ERROR_TEXT-1) && name[iin] != 0)
        {
           msg[fixed_message_ln + iin] = name[iin];
           ++iin;
        }
     msg[fixed_message_ln + iin] = 0;
     png_error(png_ptr, msg);
  }
  #endif
  #endif
  
  #ifdef PNG_SETJMP_SUPPORTED
  /* This API only exists if ANSI-C style error handling is used,
   * otherwise it is necessary for png_default_error to be overridden.
   */
  jmp_buf* PNGAPI
  png_set_longjmp_fn(png_structrp png_ptr, png_longjmp_ptr longjmp_fn,
      size_t jmp_buf_size)
  {
     /* From libpng 1.6.0 the app gets one chance to set a 'jmpbuf_size' value
      * and it must not change after that.  Libpng doesn't care how big the
      * buffer is, just that it doesn't change.
      *
      * If the buffer size is no *larger* than the size of jmp_buf when libpng is
      * compiled a built in jmp_buf is returned; this preserves the pre-1.6.0
      * semantics that this call will not fail.  If the size is larger, however,
      * the buffer is allocated and this may fail, causing the function to return
      * NULL.
      */
     if (png_ptr == NULL)
        return NULL;
  
     if (png_ptr->jmp_buf_ptr == NULL)
     {
        png_ptr->jmp_buf_size = 0; /* not allocated */
  
        if (jmp_buf_size <= (sizeof png_ptr->jmp_buf_local))
           png_ptr->jmp_buf_ptr = &png_ptr->jmp_buf_local;
  
        else
        {
           png_ptr->jmp_buf_ptr = png_voidcast(jmp_buf *,
               png_malloc_warn(png_ptr, jmp_buf_size));
  
           if (png_ptr->jmp_buf_ptr == NULL)
              return NULL; /* new NULL return on OOM */
  
           png_ptr->jmp_buf_size = jmp_buf_size;
        }
     }
  
     else /* Already allocated: check the size */
     {
        size_t size = png_ptr->jmp_buf_size;
  
        if (size == 0)
        {
           size = (sizeof png_ptr->jmp_buf_local);
           if (png_ptr->jmp_buf_ptr != &png_ptr->jmp_buf_local)
           {
              /* This is an internal error in libpng: somehow we have been left
               * with a stack allocated jmp_buf when the application regained
               * control.  It's always possible to fix this up, but for the moment
               * this is a png_error because that makes it easy to detect.
               */
              png_error(png_ptr, "Libpng jmp_buf still allocated");
              /* png_ptr->jmp_buf_ptr = &png_ptr->jmp_buf_local; */
           }
        }
  
        if (size != jmp_buf_size)
        {
           png_warning(png_ptr, "Application jmp_buf size changed");
           return NULL; /* caller will probably crash: no choice here */
        }
     }
  
     /* Finally fill in the function, now we have a satisfactory buffer. It is
      * valid to change the function on every call.
      */
     png_ptr->longjmp_fn = longjmp_fn;
     return png_ptr->jmp_buf_ptr;
  }
  
  void /* PRIVATE */
  png_free_jmpbuf(png_structrp png_ptr)
  {
     if (png_ptr != NULL)
     {
        jmp_buf *jb = png_ptr->jmp_buf_ptr;
  
        /* A size of 0 is used to indicate a local, stack, allocation of the
         * pointer; used here and in png.c
         */
        if (jb != NULL && png_ptr->jmp_buf_size > 0)
        {
  
           /* This stuff is so that a failure to free the error control structure
            * does not leave libpng in a state with no valid error handling: the
            * free always succeeds, if there is an error it gets ignored.
            */
           if (jb != &png_ptr->jmp_buf_local)
           {
              /* Make an internal, libpng, jmp_buf to return here */
              jmp_buf free_jmp_buf;
  
              if (!setjmp(free_jmp_buf))
              {
                 png_ptr->jmp_buf_ptr = &free_jmp_buf; /* come back here */
                 png_ptr->jmp_buf_size = 0; /* stack allocation */
                 png_ptr->longjmp_fn = longjmp;
                 png_free(png_ptr, jb); /* Return to setjmp on error */
              }
           }
        }
  
        /* *Always* cancel everything out: */
        png_ptr->jmp_buf_size = 0;
        png_ptr->jmp_buf_ptr = NULL;
        png_ptr->longjmp_fn = 0;
     }
  }
  #endif
  
  /* This is the default error handling function.  Note that replacements for
   * this function MUST NOT RETURN, or the program will likely crash.  This
   * function is used by default, or if the program supplies NULL for the
   * error function pointer in png_set_error_fn().
   */
  static PNG_FUNCTION(void /* PRIVATE */,
  png_default_error,(png_const_structrp png_ptr, png_const_charp error_message),
      PNG_NORETURN)
  {
  #ifdef PNG_CONSOLE_IO_SUPPORTED
  #ifdef PNG_ERROR_NUMBERS_SUPPORTED
     /* Check on NULL only added in 1.5.4 */
     if (error_message != NULL && *error_message == PNG_LITERAL_SHARP)
     {
        /* Strip "#nnnn " from beginning of error message. */
        int offset;
        char error_number[16];
        for (offset = 0; offset<15; offset++)
        {
           error_number[offset] = error_message[offset + 1];
           if (error_message[offset] == ' ')
              break;
        }
  
        if ((offset > 1) && (offset < 15))
        {
           error_number[offset - 1] = '\0';
           fprintf(stderr, "libpng error no. %s: %s",
               error_number, error_message + offset + 1);
           fprintf(stderr, PNG_STRING_NEWLINE);
        }
  
        else
        {
           fprintf(stderr, "libpng error: %s, offset=%d",
               error_message, offset);
           fprintf(stderr, PNG_STRING_NEWLINE);
        }
     }
     else
  #endif
     {
        fprintf(stderr, "libpng error: %s", error_message ? error_message :
           "undefined");
        fprintf(stderr, PNG_STRING_NEWLINE);
     }
  #else
     PNG_UNUSED(error_message) /* Make compiler happy */
  #endif
     png_longjmp(png_ptr, 1);
  }
  
  PNG_FUNCTION(void,PNGAPI
  png_longjmp,(png_const_structrp png_ptr, int val),PNG_NORETURN)
  {
  #ifdef PNG_SETJMP_SUPPORTED
     if (png_ptr != NULL && png_ptr->longjmp_fn != NULL &&
         png_ptr->jmp_buf_ptr != NULL)
        png_ptr->longjmp_fn(*png_ptr->jmp_buf_ptr, val);
  #else
     PNG_UNUSED(png_ptr)
     PNG_UNUSED(val)
  #endif
  
     /* If control reaches this point, png_longjmp() must not return. The only
      * choice is to terminate the whole process (or maybe the thread); to do
      * this the ANSI-C abort() function is used unless a different method is
      * implemented by overriding the default configuration setting for
      * PNG_ABORT().
      */
     PNG_ABORT();
  }
  
  #ifdef PNG_WARNINGS_SUPPORTED
  /* This function is called when there is a warning, but the library thinks
   * it can continue anyway.  Replacement functions don't have to do anything
   * here if you don't want them to.  In the default configuration, png_ptr is
   * not used, but it is passed in case it may be useful.
   */
  static void /* PRIVATE */
  png_default_warning(png_const_structrp png_ptr, png_const_charp warning_message)
  {
  #ifdef PNG_CONSOLE_IO_SUPPORTED
  #  ifdef PNG_ERROR_NUMBERS_SUPPORTED
     if (*warning_message == PNG_LITERAL_SHARP)
     {
        int offset;
        char warning_number[16];
        for (offset = 0; offset < 15; offset++)
        {
           warning_number[offset] = warning_message[offset + 1];
           if (warning_message[offset] == ' ')
              break;
        }
  
        if ((offset > 1) && (offset < 15))
        {
           warning_number[offset + 1] = '\0';
           fprintf(stderr, "libpng warning no. %s: %s",
               warning_number, warning_message + offset);
           fprintf(stderr, PNG_STRING_NEWLINE);
        }
  
        else
        {
           fprintf(stderr, "libpng warning: %s",
               warning_message);
           fprintf(stderr, PNG_STRING_NEWLINE);
        }
     }
     else
  #  endif
  
     {
        fprintf(stderr, "libpng warning: %s", warning_message);
        fprintf(stderr, PNG_STRING_NEWLINE);
     }
  #else
     PNG_UNUSED(warning_message) /* Make compiler happy */
  #endif
     PNG_UNUSED(png_ptr) /* Make compiler happy */
  }
  #endif /* WARNINGS */
  
  /* This function is called when the application wants to use another method
   * of handling errors and warnings.  Note that the error function MUST NOT
   * return to the calling routine or serious problems will occur.  The return
   * method used in the default routine calls longjmp(png_ptr->jmp_buf_ptr, 1)
   */
  void PNGAPI
  png_set_error_fn(png_structrp png_ptr, png_voidp error_ptr,
      png_error_ptr error_fn, png_error_ptr warning_fn)
  {
     if (png_ptr == NULL)
        return;
  
     png_ptr->error_ptr = error_ptr;
     png_ptr->error_fn = error_fn;
  #ifdef PNG_WARNINGS_SUPPORTED
     png_ptr->warning_fn = warning_fn;
  #else
     PNG_UNUSED(warning_fn)
  #endif
  }
  
  
  /* This function returns a pointer to the error_ptr associated with the user
   * functions.  The application should free any memory associated with this
   * pointer before png_write_destroy and png_read_destroy are called.
   */
  png_voidp PNGAPI
  png_get_error_ptr(png_const_structrp png_ptr)
  {
     if (png_ptr == NULL)
        return NULL;
  
     return ((png_voidp)png_ptr->error_ptr);
  }
  
  
  #ifdef PNG_ERROR_NUMBERS_SUPPORTED
  void PNGAPI
  png_set_strip_error_numbers(png_structrp png_ptr, png_uint_32 strip_mode)
  {
     if (png_ptr != NULL)
     {
        png_ptr->flags &=
           ((~(PNG_FLAG_STRIP_ERROR_NUMBERS |
           PNG_FLAG_STRIP_ERROR_TEXT))&strip_mode);
     }
  }
  #endif
  
  #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) ||\
     defined(PNG_SIMPLIFIED_WRITE_SUPPORTED)
     /* Currently the above both depend on SETJMP_SUPPORTED, however it would be
      * possible to implement without setjmp support just so long as there is some
      * way to handle the error return here:
      */
  PNG_FUNCTION(void /* PRIVATE */, (PNGCBAPI
  png_safe_error),(png_structp png_nonconst_ptr, png_const_charp error_message),
      PNG_NORETURN)
  {
     png_const_structrp png_ptr = png_nonconst_ptr;
     png_imagep image = png_voidcast(png_imagep, png_ptr->error_ptr);
  
     /* An error is always logged here, overwriting anything (typically a warning)
      * that is already there:
      */
     if (image != NULL)
     {
        png_safecat(image->message, (sizeof image->message), 0, error_message);
        image->warning_or_error |= PNG_IMAGE_ERROR;
  
        /* Retrieve the jmp_buf from within the png_control, making this work for
         * C++ compilation too is pretty tricky: C++ wants a pointer to the first
         * element of a jmp_buf, but C doesn't tell us the type of that.
         */
        if (image->opaque != NULL && image->opaque->error_buf != NULL)
           longjmp(png_control_jmp_buf(image->opaque), 1);
  
        /* Missing longjmp buffer, the following is to help debugging: */
        {
           size_t pos = png_safecat(image->message, (sizeof image->message), 0,
               "bad longjmp: ");
           png_safecat(image->message, (sizeof image->message), pos,
               error_message);
        }
     }
  
     /* Here on an internal programming error. */
     abort();
  }
  
  #ifdef PNG_WARNINGS_SUPPORTED
  void /* PRIVATE */ PNGCBAPI
  png_safe_warning(png_structp png_nonconst_ptr, png_const_charp warning_message)
  {
     png_const_structrp png_ptr = png_nonconst_ptr;
     png_imagep image = png_voidcast(png_imagep, png_ptr->error_ptr);
  
     /* A warning is only logged if there is no prior warning or error. */
     if (image->warning_or_error == 0)
     {
        png_safecat(image->message, (sizeof image->message), 0, warning_message);
        image->warning_or_error |= PNG_IMAGE_WARNING;
     }
  }
  #endif
  
  int /* PRIVATE */
  png_safe_execute(png_imagep image, int (*function)(png_voidp), png_voidp arg)
  {
     png_voidp saved_error_buf = image->opaque->error_buf;
     jmp_buf safe_jmpbuf;
     int result;
  
     /* Safely execute function(arg), with png_error returning back here. */
     if (setjmp(safe_jmpbuf) == 0)
     {
        image->opaque->error_buf = safe_jmpbuf;
        result = function(arg);
        image->opaque->error_buf = saved_error_buf;
        return result;
     }
  
     /* On png_error, return via longjmp, pop the jmpbuf, and free the image. */
     image->opaque->error_buf = saved_error_buf;
     png_image_free(image);
     return 0;
  }
  #endif /* SIMPLIFIED READ || SIMPLIFIED_WRITE */
  #endif /* READ || WRITE */
  

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