| // 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/dsp/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 |
| } |