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 // Copyright ©2018 The Gonum Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package fourier import "gonum.org/v1/gonum/fourier/internal/fftpack" // DCT implements Discrete Cosine Transform for real sequences. type DCT struct { work []float64 ifac [15]int } // NewDCT returns a DCT initialized for work on sequences of length n. // NewDCT will panic is n is not greater than 1. func NewDCT(n int) *DCT { var t DCT t.Reset(n) return &t } // Len returns the length of the acceptable input. func (t *DCT) Len() int { return len(t.work) / 3 } // Reset reinitializes the DCT for work on sequences of length n. // Reset will panic is n is not greater than 1. func (t *DCT) Reset(n int) { if n <= 1 { panic("fourier: n less than 2") } if 3*n <= cap(t.work) { t.work = t.work[:3*n] } else { t.work = make([]float64, 3*n) } fftpack.Costi(n, t.work, t.ifac[:]) } // Transform computes the Discrete Fourier Cosine Transform of // the input data, src, placing the result in dst and returning it. // This transform is unnormalized; a call to Transform followed by // another call to Transform will multiply the input sequence by 2*(n-1), // where n is the length of the sequence. // // If the length of src is not t.Len(), Transform will panic. // If dst is nil, a new slice is allocated and returned. If dst is not nil and // the length of dst does not equal t.Len(), FFT will panic. // It is safe to use the same slice for dst and src. func (t *DCT) Transform(dst, src []float64) []float64 { if len(src) != t.Len() { panic("fourier: sequence length mismatch") } if dst == nil { dst = make([]float64, t.Len()) } else if len(dst) != t.Len() { panic("fourier: destination length mismatch") } copy(dst, src) fftpack.Cost(len(dst), dst, t.work, t.ifac[:]) return dst } // DST implements Discrete Sine Transform for real sequences. type DST struct { work []float64 ifac [15]int } // NewDST returns a DST initialized for work on sequences of length n. func NewDST(n int) *DST { var t DST t.Reset(n) return &t } // Len returns the length of the acceptable input. func (t *DST) Len() int { return (2*len(t.work)+1)/5 - 1 } // Reset reinitializes the DCT for work on sequences of length n. func (t *DST) Reset(n int) { if 5*(n+1)/2 <= cap(t.work) { t.work = t.work[:5*(n+1)/2] } else { t.work = make([]float64, 5*(n+1)/2) } fftpack.Sinti(n, t.work, t.ifac[:]) } // Transform computes the Discrete Fourier Sine Transform of the input // data, src, placing the result in dst and returning it. // This transform is unnormalized; a call to Transform followed by // another call to Transform will multiply the input sequence by 2*(n-1), // where n is the length of the sequence. // // If the length of src is not t.Len(), Transform will panic. // If dst is nil, a new slice is allocated and returned. If dst is not nil and // the length of dst does not equal t.Len(), FFT will panic. // It is safe to use the same slice for dst and src. func (t *DST) Transform(dst, src []float64) []float64 { if len(src) != t.Len() { panic("fourier: sequence length mismatch") } if dst == nil { dst = make([]float64, t.Len()) } else if len(dst) != t.Len() { panic("fourier: destination length mismatch") } copy(dst, src) fftpack.Sint(len(dst), dst, t.work, t.ifac[:]) return dst }