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README.md

SYLT-FFT

DEVSOUND (I)FFT(R) LIBRARY

And some other funky fixed-point maths like gray-coding and pow(2, f)

Optimized (C-level) for Keil C Compiler and GCC on Cortex-M4.

Authors:

  • D. Taylor 2014 (gmail: senseitg)

License:

  • MHG (GPL compatible) - see LICENSE

Features:

  • FFT (Fast Fourier Transform) and IFFT (Inverse FFT)
  • Fixed-point 32-bit, Radix-2
  • Complex or real (with slight conversion overhead) data
  • No plan construction required before (I)FFT
  • No reliance on other libraries (including libm if using precomputed tables)

Options (config.h):

  • DIT (decimation-in-time) or DIF (decimation-in-frequency)
  • Rounding on divide (-speed, +accuracy)
  • Saturating math (-speed, +stability)
  • Table size vs. max. FFT length

Resource requirements:

  • Minimal memory requirements (in-place)
  • Minimal stack use (non-recursive)
  • Minimal twiddle tables (512 bytes for max N=512 FFT)

Notes:

  • Designed for optimal performance, not optimal accuracy

Caveats:

  • Care must be taken with input data to ensure no overflows
  • Requires C99 (-std=c99 for GCC)

Performance:

  • Comparing against: CMSIS DSP arm_cortexM4I_math.lib(1.4.2)
  • Platform: Freescale Kinetis K20 (Cortex-M4/ARMv7E-M)
  • KEIL = Keil C Compiler 5.01 -O3
  • GCC = GNU Tools for ARM Embedded Processors 4.8.4 -O3
Comparisons are of speed, +N% = faster than CMSIS, -N% = slower.
Please verify and do additional tests to add to the list.

  CMSIS-DSP             SYLT-FFT      N     KEIL     GCC
* arm_cfft_radix2_q31   fft_inverse   256   +25.6%   +15.1%

Thanks to:

  • Wikipedia - for existing and taking donations
  • KATJA - for intelligible merge/split spectra algorithm
  • XCORE - for intelligible (I)FFT algorithm
  • CMLAB - for intelligible FFT algorithm breakdown
  • BEVAN - for intelligible DIT vs. DIF, radix-2 vs. 4 overview

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