criterium.stats.fft — org.hugoduncan/criterium 0.5.245-ALPHA

Pure Clojure radix-2 Cooley-Tukey FFT implementation.

Provides O(n log n) Fast Fourier Transform for autocorrelation computation. Uses interleaved complex representation [re0 im0 re1 im1 ...] for cache efficiency. All operations use primitive double arrays with zero garbage allocation during transform execution.

Main functions:

• fft! / fft - Forward FFT (in-place / copying)
• ifft! / ifft - Inverse FFT (in-place / copying)
• next-power-of-2 - Find smallest power of 2 >= n
• zero-pad-real - Zero-pad real signal to power-of-2 length

Complex arrays use interleaved format: [re0 im0 re1 im1 ...] Array length is 2*n where n is the number of complex samples.

complex->real clj

(complex->real complex-arr)

Extracts real parts from interleaved complex array. Output length is half the input length.

complex-magnitude clj

(complex-magnitude complex-arr)

Computes magnitude of each complex sample. Output length is half the input length.

fft clj

(fft arr)

Forward FFT on interleaved complex array. Returns a new array with the FFT result; input is not modified. The array must have length 2*n where n is a power of 2.

Input/output format: [re0 im0 re1 im1 ... re_{n-1} im_{n-1}]

fft! clj

(fft! arr)

In-place forward FFT on interleaved complex array. The array must have length 2*n where n is a power of 2. Modifies arr in place and returns it.

Input/output format: [re0 im0 re1 im1 ... re_{n-1} im_{n-1}]

Uses standard DFT sign convention: X[k] = Σ x[n] * e^{-i 2π k n / N}

ifft clj

(ifft arr)

Inverse FFT on interleaved complex array. Returns a new array with the IFFT result; input is not modified. The array must have length 2*n where n is a power of 2. Result is scaled by 1/n.

Input/output format: [re0 im0 re1 im1 ... re_{n-1} im_{n-1}]

ifft! clj

(ifft! arr)

In-place inverse FFT on interleaved complex array. The array must have length 2*n where n is a power of 2. Modifies arr in place and returns it. Result is scaled by 1/n.

Input/output format: [re0 im0 re1 im1 ... re_{n-1} im_{n-1}]

Uses standard IDFT sign convention: x[n] = (1/N) Σ X[k] * e^{+i 2π k n / N}

next-power-of-2 clj

(next-power-of-2 n)

Returns the smallest power of 2 greater than or equal to n. For n <= 0, returns 1.

power-of-2? clj

(power-of-2? n)

Returns true if n is a positive power of 2.

real->complex clj

(real->complex real-arr)

Converts a real signal to interleaved complex format. Imaginary parts are set to zero. Output length is 2 * (length of input).

zero-pad-for-autocorrelation clj

(zero-pad-for-autocorrelation real-arr)

Zero-pads a real signal to 2*next-power-of-2(n) for autocorrelation. This provides sufficient padding to compute circular correlation equivalent to linear correlation.

zero-pad-real clj

(zero-pad-real real-arr)

(zero-pad-real real-arr target-n)

Zero-pads a real signal to the specified power-of-2 length. Returns interleaved complex array with zero imaginary parts. If target-n is not specified, pads to next power of 2 >= (length input). If target-n is specified, it must be a power of 2 >= (length input).