gonum.org/v1/gonum@v0.14.0/dsp/fourier/sincos.go (about)

     1  // Copyright ©2018 The Gonum Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package fourier
     6  
     7  import "gonum.org/v1/gonum/dsp/fourier/internal/fftpack"
     8  
     9  // DCT implements Discrete Cosine Transform for real sequences.
    10  type DCT struct {
    11  	work []float64
    12  	ifac [15]int
    13  }
    14  
    15  // NewDCT returns a DCT initialized for work on sequences of length n.
    16  // NewDCT will panic is n is not greater than 1.
    17  func NewDCT(n int) *DCT {
    18  	var t DCT
    19  	t.Reset(n)
    20  	return &t
    21  }
    22  
    23  // Len returns the length of the acceptable input.
    24  func (t *DCT) Len() int { return len(t.work) / 3 }
    25  
    26  // Reset reinitializes the DCT for work on sequences of length n.
    27  // Reset will panic is n is not greater than 1.
    28  func (t *DCT) Reset(n int) {
    29  	if n <= 1 {
    30  		panic("fourier: n less than 2")
    31  	}
    32  	if 3*n <= cap(t.work) {
    33  		t.work = t.work[:3*n]
    34  	} else {
    35  		t.work = make([]float64, 3*n)
    36  	}
    37  	fftpack.Costi(n, t.work, t.ifac[:])
    38  }
    39  
    40  // Transform computes the Discrete Fourier Cosine Transform of
    41  // the input data, src, placing the result in dst and returning it.
    42  // This transform is unnormalized; a call to Transform followed by
    43  // another call to Transform will multiply the input sequence by 2*(n-1),
    44  // where n is the length of the sequence.
    45  //
    46  // If the length of src is not t.Len(), Transform will panic.
    47  // If dst is nil, a new slice is allocated and returned. If dst is not nil and
    48  // the length of dst does not equal t.Len(), FFT will panic.
    49  // It is safe to use the same slice for dst and src.
    50  func (t *DCT) Transform(dst, src []float64) []float64 {
    51  	if len(src) != t.Len() {
    52  		panic("fourier: sequence length mismatch")
    53  	}
    54  	if dst == nil {
    55  		dst = make([]float64, t.Len())
    56  	} else if len(dst) != t.Len() {
    57  		panic("fourier: destination length mismatch")
    58  	}
    59  	copy(dst, src)
    60  	fftpack.Cost(len(dst), dst, t.work, t.ifac[:])
    61  	return dst
    62  }
    63  
    64  // DST implements Discrete Sine Transform for real sequences.
    65  type DST struct {
    66  	work []float64
    67  	ifac [15]int
    68  }
    69  
    70  // NewDST returns a DST initialized for work on sequences of length n.
    71  func NewDST(n int) *DST {
    72  	var t DST
    73  	t.Reset(n)
    74  	return &t
    75  }
    76  
    77  // Len returns the length of the acceptable input.
    78  func (t *DST) Len() int { return (2*len(t.work)+1)/5 - 1 }
    79  
    80  // Reset reinitializes the DCT for work on sequences of length n.
    81  func (t *DST) Reset(n int) {
    82  	if 5*(n+1)/2 <= cap(t.work) {
    83  		t.work = t.work[:5*(n+1)/2]
    84  	} else {
    85  		t.work = make([]float64, 5*(n+1)/2)
    86  	}
    87  	fftpack.Sinti(n, t.work, t.ifac[:])
    88  }
    89  
    90  // Transform computes the Discrete Fourier Sine Transform of the input
    91  // data, src, placing the result in dst and returning it.
    92  // This transform is unnormalized; a call to Transform followed by
    93  // another call to Transform will multiply the input sequence by 2*(n-1),
    94  // where n is the length of the sequence.
    95  //
    96  // If the length of src is not t.Len(), Transform will panic.
    97  // If dst is nil, a new slice is allocated and returned. If dst is not nil and
    98  // the length of dst does not equal t.Len(), FFT will panic.
    99  // It is safe to use the same slice for dst and src.
   100  func (t *DST) Transform(dst, src []float64) []float64 {
   101  	if len(src) != t.Len() {
   102  		panic("fourier: sequence length mismatch")
   103  	}
   104  	if dst == nil {
   105  		dst = make([]float64, t.Len())
   106  	} else if len(dst) != t.Len() {
   107  		panic("fourier: destination length mismatch")
   108  	}
   109  	copy(dst, src)
   110  	fftpack.Sint(len(dst), dst, t.work, t.ifac[:])
   111  	return dst
   112  }