v0.17.0

FFT kernel builders (#28)

go-fft's SIMD kernel generators now live here, one package per architecture:

• fft/amd64:

  • Stockham passes of radix 2, 3, 4, 5, 8, 9, 10, 12, 15, 16 and 20 (AVX2), and radix 2, 4 and 8 at 512 bits;
  • final, batched, strided and run-writing passes;
  • the split layouts at 256 and 512 bits;
  • float32 passes;
  • the real-FFT untangle and retangle;
  • SSE2 and AVX2 complex products;
  • the two- and three-pass stack-frame trampolines and their address table.

  Kernels.FMA builds the fused twins: the twiddle product, radix 8's √2/2, and the radix-9 and -16 internal twiddles.

• fft/arm64:

  • NEON passes of radix 2, 3, 4, 5 and 8 in float64 and float32: pass, final pass, batched pass, block-split layout;
  • the untangle and retangle;
  • the complex product.

• fft/riscv64 and fft/s390x: the RVV and vector-facility complex products.

Each builder appends one TEXT block to an emit.File. The caller supplies:

• the symbol;
• the constants-table offsets (Consts, SplitConsts);
• on amd64, FMA.

The arguments, registers and frame are the kernel's own, and are documented on each builder.

Verification:

• Every file go-fft generates is pinned, by SHA-256, to the bytes go-fft commits. That covers go-fft main's 21 .s files and the 3 FMA files of its Round 41 branch.
• Golden files pin one or two kernels of every builder.
• Every kernel goes through the Go assembler.
• examples/fft/<arch> runs the complex products and a 16-point FFT on each architecture.
• The library gate covers ./fft/... at 100%.

No change to the existing packages.