Zigzag Decoding with AVX-512
17 hours ago
- #Zigzag Decoding
- #AVX-512
- #Optimization
- The article explores two optimizations for zigzag decoding using AVX-512, focusing on meshoptimizer's vertex decoding.
- Zigzag encoding transforms signed integers into unsigned values for efficient compression, with decoding formulas involving bitwise operations.
- A mask-based optimization uses AVX-512 predication (e.g., vptestmd) to reduce instruction count, but may increase latency and is compiler-dependent.
- A GF(2) affine transformation optimization employs the vgf2p8affineqb instruction for 8-bit values, offering a single-instruction solution with potential throughput gains.
- Both optimizations face limitations: the mask trick's latency impact and reliance on compiler behavior, and GFNI's restriction to 8-bit widths and availability concerns.
- Experimental results show mixed performance improvements, with context-dependent benefits due to other bottlenecks like latency spines or store throughput.