Commit 147548c0559c6eee4fce946aec29bda41823e21d
2021-09-06T11:31:37
Neon/AArch64: Accelerate Huffman encoding - Make better use of 128-bit vector registers, thus reducing the number of Neon instructions required to construct the AC coefficient bitmap. - Refactor the Neon computations of 'nbits' and 'diff' to use shorter and higher-throughput instruction sequences. DRC's notes: This commit partially integrates #570. Arm reported a 1-4% speedup on Cortex-A55 and Neoverse-N1 cores when using recent compilers but little or no speedup with Clang 10. I observed no speedup with Clang 10 on my Cortex-A53 and Cortex-A72 cores. Thus, referring to #582, the primary purpose of this commit is to fix UBSan warnings regarding the shift operations previously located at Line 253: https://github.com/libjpeg-turbo/libjpeg-turbo/blob/d640a457305164417a60f30c6457d316f0b44a9d/simd/arm/aarch64/jchuff-neon.c#L253