NEON SIMD Instructions

NEON Is Mandatory on AArch64

NEON shares v0-v31 (128-bit) for SIMD and scalar FP. ffmpeg, libvpx, and Apple's image pipelines maintain thousands of lines of hand-written NEON because auto-vectorization misses on alias analysis. One fadd v0.4s, v1.4s, v2.4s adds four floats in parallel.

asmCopy
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Lane suffixes:

• .4s: four 32-bit floats
• .2d: two doubles
• .8h: eight halfwords

Loads/stores use ld1/st1 with brace syntax; alignment still helps DRAM throughput.

For this exercise, you will add two four-float arrays with NEON and write results back. This task asks you to keep addresses 16-byte aligned where possible, because unaligned vector loads trap or slow down on some cores and silently hurt battery life on mobile SoCs.

Keep the relevant man page, ABI doc, or Rust reference chapter open while you work. When your output disagrees with the reference implementation on the same machine, the mismatch is usually an alignment rule, an off-by-one terminator, or a register slot you misread in GDB. Skim the official documentation for the tool or ABI named in the exercise; the prose changes, but register roles, syscall numbers, and ownership rules stay stable across releases. Treat each failure as a contract test: the CPU, kernel, and borrow checker enforce rules whether or not the tutorial mentioned them explicitly.