xref: /aosp_15_r20/external/libjpeg-turbo/README.chromium (revision dfc6aa5c1cfd4bc4e2018dc74aa96e29ee49c6da)

Name: libjpeg-turbo
URL: https://github.com/libjpeg-turbo/libjpeg-turbo/
Version: 2.1.5.1
License: IJG, BSD-3, Zlib
License File: LICENSE.md
Security Critical: yes
Shipped: yes
License Android Compatible: yes

Description:
This consists of the components:
* libjpeg-turbo 2.1.5.1
* This file (README.chromium)
* A build file (BUILD.gn)
* An OWNERS file
* A codereview.settings file
* A DIR_METADATA file
* Patched header files used by Chromium
* Deleted unused directories: .github, cmakescripts, doc, fuzz, java, release,
  sharedlib, simd/mips, simd/mips64, simd/powerpc, and win
* Deleted unused files: appveyor.yml, CMakeLists.txt, cjpeg.1, croptest.in,
  djpeg.1, doxygen.config, doxygen-extra.css, example.txt, .gitattributes,
  jpegtran.1, md5/CMakeLists.txt, md5/md5cmp.c, rdjpgcom.1, simd/CMakeLists.txt,
  strtest.c, tjbenchtest.in, tjbenchtest.java.in, tjexample.c, tjexampletest.in,
  tjexampletest.java.in and wrjpgcom.1
* Deleted legacy Arm Neon assembly files (supporting old compiler versions that
  do not generate performant code from intrinsics):
  simd/arm/aarch32/jsimd_neon.S, simd/arm/aarch64/jsimd_neon.S.

This libjpeg-turbo can replace our libjpeg-6b without any modifications in the
Chromium code.

Same as our copy of libjpeg-6b, this libjpeg-turbo also added a new file
jpeglibmangler.h and included it from jpeglib.h that changes the names of all
externally visible functions to chromium_* so that we can avoid conflicts that
arise when system libraries attempt to use our libjpeg. Also, we applied the
following changes which are not merged to upstream:

* Configuration files jconfig.h, jconfigint.h and neon-compat.h were generated
  and then altered manually to be compatible on all of Chromium's platforms.
  http://crbug.com/608347
* Fix static const data duplication of jpeg_nbits_table. A unique copy
  was in the jchuff.obj and jcphuff.obj resulting in an added 65k in
  .rdata in chrome.dll and chrome_child.dll.  Declaring extern const
  in the header instead of static const and moving the definition to
  a new .c file fixes this so only one copy is referenced. Also added
  extern wrappers around usage in asm files. The jpeg_nbits_table.inc
  file was also deleted. It was also necessary to give this table hidden
  visibility to avoid invalid relocations (ignored by ld but rejected by
  lld) arising from attempts to reference the table from assembler on
  32-bit x86. This only affects shared libraries, but that's important
  for downstream Android builds.
* Merged upstream patch https://github.com/libjpeg-turbo/libjpeg-turbo/commit/0fc7313e545a3ff499c19ee6591bb87f0ad8b2a4
  This patch resolves an O(n^2) slowdown issue when JPEG files contain an
  enormous number of markers; this would only occur in a maliciouly-crafted
  image, or through fuzzing.
* Patches to enable running the upstream unit tests through GTest.
  The upstream unit tests are defined here under the section 'TESTS':
  https://github.com/libjpeg-turbo/libjpeg-turbo/blob/master/CMakeLists.txt
  These changes are tracked by Chromium issue: https://crbug.com/993876
  - Refactor tjunittest.c to provide test interface
  - Move tjunittest logs from stdout to stderr
  - Refactor tjbench.c to provide test interface
  - Move tbench logs from stdout to stderr
  - Write tjunittest output files to sdcard on Android
  - Refactor cjpeg.c to provide test interface
  - Refactor jpegtran.c to provide test interface
  - Add input JPEG images for djpeg and jpegtran tests
  - Refactor djpeg.c to provide test interface
  A new gtest directory contains GTest wrappers (and associated utilities) for
  each of tjunittest, tjbench, cjpeg, djpeg and jpegtran.

Refer to working-with-nested-repos [1] for details of how to setup your git
svn client to update the code (for making local changes, cherry picking from
upstream, etc).

[1] https://www.chromium.org/developers/how-tos/get-the-code/working-with-nested-repos