kc3-lang/libpng/contrib/pngexif/bytepack.py

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• Hash : ec2e58c1
  Author :
  Date : 2024-02-22T11:32:53
  

  pngexif: Import pngexifinfo as an externally-contributed project
  
  We used this experimental project in the development of the PNG-EXIF
  ("eXIf") specification, back in 2017. The project evolved together
  with the draft specification, which was finalized on 2017-Jun-15 and
  approved by the PNG Group on 2017-Jul-13.
  
  The EXIF specification, outside of the scope of PNG and libpng, is
  quite complex. The libpng implementation cannot grow too much beyond
  performing basic integrity checks on top of serialization. In order
  to create and manipulate PNG-EXIF image files, the use of external
  libraries and tools such as ExifTool is necessary.
  
  Now, with the addition of contrib/pngexif to the libpng repository,
  offline tasks like metadata inspection and linting can be performed
  without importing external dependencies.
  

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• contrib/pngexif/bytepack.py

• #!/usr/bin/env python
  
  """
  Byte packing and unpacking utilities.
  
  Copyright (C) 2017-2020 Cosmin Truta.
  
  Use, modification and distribution are subject to the MIT License.
  Please see the accompanying file LICENSE_MIT.txt
  """
  
  from __future__ import absolute_import, division, print_function
  
  import struct
  
  
  def unpack_uint32be(buffer, offset=0):
      """Unpack an unsigned int from its 32-bit big-endian representation."""
      return struct.unpack(">I", buffer[offset:offset + 4])[0]
  
  
  def unpack_uint32le(buffer, offset=0):
      """Unpack an unsigned int from its 32-bit little-endian representation."""
      return struct.unpack("<I", buffer[offset:offset + 4])[0]
  
  
  def unpack_uint16be(buffer, offset=0):
      """Unpack an unsigned int from its 16-bit big-endian representation."""
      return struct.unpack(">H", buffer[offset:offset + 2])[0]
  
  
  def unpack_uint16le(buffer, offset=0):
      """Unpack an unsigned int from its 16-bit little-endian representation."""
      return struct.unpack("<H", buffer[offset:offset + 2])[0]
  
  
  def unpack_uint8(buffer, offset=0):
      """Unpack an unsigned int from its 8-bit representation."""
      return struct.unpack("B", buffer[offset:offset + 1])[0]
  
  
  if __name__ == "__main__":
      # For testing only.
      assert unpack_uint32be(b"ABCDEF", 1) == 0x42434445
      assert unpack_uint32le(b"ABCDEF", 1) == 0x45444342
      assert unpack_uint16be(b"ABCDEF", 1) == 0x4243
      assert unpack_uint16le(b"ABCDEF", 1) == 0x4342
      assert unpack_uint8(b"ABCDEF", 1) == 0x42
  

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