tree 052422c6a4c012049279997bf39fda10244fa78d
parent e795afc330666f10d188e2c470dc00700062f666
author Jonathan Wright <jonathan.wright@arm.com> 1612975550 +0000
committer DRC <information@libjpeg-turbo.org> 1616785750 -0500

Neon: Use byte-swap builtins instead of inline asm

Define compiler-independent byte-swap macros and use them instead of
executing 'rev' via inline assembly code with GCC-compatible compilers
or a slow shift-store sequence with Visual C++.

* This produces identical assembly code with:

  - 64-bit GCC 8.4.0 (Linux)
  - 64-bit GCC 9.3.0 (Linux)
  - 64-bit Clang 10.0.0 (Linux)
  - 64-bit Clang 10.0.0 (MinGW)
  - 64-bit Clang 12.0.0 (Xcode 12.2, macOS)
  - 64-bit Clang 12.0.0 (Xcode 12.2, iOS)

* This produces different assembly code with:

  - 64-bit GCC 4.9.1 (Linux)
  - 32-bit GCC 4.8.2 (Linux)
  - 32-bit GCC 8.4.0 (Linux)
  - 32-bit GCC 9.3.0 (Linux)
    Since the intrinsics implementation of Huffman encoding is not used
    by default with these compilers, this is not a concern.

  - 32-bit Clang 10.0.0 (Linux)
    Verified performance neutrality

Closes #507