86 lines
2.9 KiB
Scheme
86 lines
2.9 KiB
Scheme
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;;; FFT - Fast Fourier Transform, translated from "Numerical Recipes in C"
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(library (r6rs-benchmarks fft)
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(export main)
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(import (r6rs) (r6rs arithmetic flonums) (r6rs-benchmarks))
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(define flsin sin)
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(define (four1 data)
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(let ((n (vector-length data))
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(pi*2 6.28318530717959)) ; to compute the inverse, negate this value
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; bit-reversal section
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(let loop1 ((i 0) (j 0))
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(if (< i n)
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(begin
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(if (< i j)
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(begin
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(let ((temp (vector-ref data i)))
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(vector-set! data i (vector-ref data j))
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(vector-set! data j temp))
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(let ((temp (vector-ref data (+ i 1))))
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(vector-set! data (+ i 1) (vector-ref data (+ j 1)))
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(vector-set! data (+ j 1) temp))))
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(let loop2 ((m (quotient n 2)) (j j))
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(if (and (>= m 2) (>= j m))
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(loop2 (quotient m 2) (- j m))
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(loop1 (+ i 2) (+ j m)))))))
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; Danielson-Lanczos section
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(let loop3 ((mmax 2))
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(if (< mmax n)
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(let* ((theta
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(fl/ pi*2 (exact->inexact mmax)))
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(wpr
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(let ((x (flsin (fl* 0.5 theta))))
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(fl* -2.0 (fl* x x))))
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(wpi
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(flsin theta)))
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(let loop4 ((wr 1.0) (wi 0.0) (m 0))
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(if (< m mmax)
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(begin
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(let loop5 ((i m))
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(if (< i n)
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(let* ((j
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(+ i mmax))
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(tempr
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(fl-
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(fl* wr (vector-ref data j))
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(fl* wi (vector-ref data (+ j 1)))))
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(tempi
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(fl+
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(fl* wr (vector-ref data (+ j 1)))
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(fl* wi (vector-ref data j)))))
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(vector-set! data j
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(fl- (vector-ref data i) tempr))
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(vector-set! data (+ j 1)
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(fl- (vector-ref data (+ i 1)) tempi))
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(vector-set! data i
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(fl+ (vector-ref data i) tempr))
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(vector-set! data (+ i 1)
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(fl+ (vector-ref data (+ i 1)) tempi))
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(loop5 (+ j mmax)));***))
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(loop4 (fl+ (fl- (fl* wr wpr) (fl* wi wpi)) wr)
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(fl+ (fl+ (fl* wi wpr) (fl* wr wpi)) wi)
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(+ m 2)))))
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));******
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(loop3 (* mmax 2)))))))
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(define data
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(make-vector 1024 0.0))
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(define (run data)
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(four1 data)
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(vector-ref data 0))
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(define (main . args)
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(run-benchmark
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"fft"
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fft-iters
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(lambda (result) (equal? result 0.0))
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(lambda (data) (lambda () (run data)))
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data)))
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