Neon

Data is organised in 5 bytes chunks to store 4 x RAW10 pixel data:

• 4 bytes of 8bit MSB of 10bit
• 1 byte of 4 x 2bit LSB

General idea:

• Load data
  • Neon can perform interleaved loads by 4
  • Neon can use lookup table load, so we can specify what byte loads where
• Extend 8 bit vectors to 16bit vectors
  • max register size ? 128bit so 16 x 8 bit or 8 x 16bit. Load only 8x 8bit to extend it to 8x16bit ? Or split using vget_low_s8() ?
  • with shift left by 2 ?
• ??? How to insert 2 LSB bits ?
  • Create 3 more copies of byte with LSB bits
  • In each copy, organise bits to be in correct place.
  • Insert bits to 16bit OR - there is instruction to insert and shift ???
• Store data:
  • Interleaved store by 3

Useful info on ARM:

• libTIFF optimization: CMYK to RGBA conversion
• Chromium optimization: pre-multiplied alpha channel data
• https://developer.arm.com/documentation/102159/0400/Shifting-left-and-right?lang=en
• Load and store - example RGB conversion
• RGB to grayscale conversion
• https://developer.arm.com/documentation/den0018/a/NEON-Code-Examples-with-Optimization/Converting-color-depth/Converting-from-RGB565-to-RGB888
• Coding for Neon - Part 4: Shifting Left and Right

Useful info:

• Unpacking int8x16_t into a pair of int16x8 & packing a pair of int16x8_t into a int8x16_t
• https://stackoverflow.com/questions/44353277/how-to-code-ai-bci-on-arm-neon-simd-intrinsic-function
• rgb2yuv-neon
• ARM Neon and Base64 encoding & decoding
• Pruning spaces faster on ARM processors with Vector Table Lookups
• ARM processor NEON programming and optimization techniques - shift operations such as left shift and right shift

From https://stackoverflow.com/questions/71554911/how-to-vectorize-2d-array-using-neon-intrinsics:

Consider using OpenMP, add #pragma omp parallel for before for loop and -fopenmp to the compiler cmdline

Auto vectorization in GCC:

• Vectorization optimization in GCC

Instead of using ARM Neon, use OpenCV wrapper which provides portability across platforms:

• https://answers.opencv.org/question/224485/simd-optimizations-get-no-performance-gains-on-arm-neon/