| 2019/08/13(Tue) 00:01:21 編集(投稿者)
追記：拡張メソッドの不具合修正
■No91912 (えんえん さん) に返信
> Dim ar2 As New ArraySegment(Of Double)(ar, r, ar.length - r)
> が正しいのでしょうか？
> 要素数を最後まで指定しないといけないですよね？
そうなりますね。
処理を分かりやすくするために、ArraySegment のための
拡張メソッドを用意しておくのが良いでしょう。
後述のコードを用意しておけば、
// 元の C++ 実装
tmpr[m * n_radix + j] = xr * wr - xi * wi;
に相当する処理を、
tmpr.SetValue(m * n_radix + j, xr * wr - xi * wi)
の構文で書ける様になります。
また、再帰呼び出しの
// C++
fft(n_radix, theta * radix, &tmpr[r], &tmpi[r], ar, ai);
についても、
fft(n_radix, theta * radix, tmpi.AsSegment(r), tmpi.AsSegment(r), ar, ai)
で済むようになります。
'----------------------
Module ArraySegmentExtension
<System.Runtime.CompilerServices.Extension>
Public Function AsSegment(Of T)(this As T()) As ArraySegment(Of T)
Return New ArraySegment(Of T)(this)
End Function
<System.Runtime.CompilerServices.Extension>
Public Function AsSegment(Of T)(this As T(), start As Integer) As ArraySegment(Of T)
Return New ArraySegment(Of T)(this, start, this.Length - start)
End Function
<System.Runtime.CompilerServices.Extension>
Public Function AsSegment(Of T)(this As ArraySegment(Of T), start As Integer) As ArraySegment(Of T)
'Return New ArraySegment(Of T)(this.Array, this.Offset + start, this.ToArray.Length - this.Offset - start)
Return New ArraySegment(Of T)(this.Array, this.Offset + start, this.Array.Length - this.Offset - start)
End Function
<System.Runtime.CompilerServices.Extension>
Public Function AsSegment(Of T)(this As ArraySegment(Of T), start As Integer, length As Integer) As ArraySegment(Of T)
Return New ArraySegment(Of T)(this.Array, this.Offset + start, length)
End Function
<System.Runtime.CompilerServices.Extension>
Public Function AsSegment(Of T)(this As T(), start As Integer, length As Integer) As ArraySegment(Of T)
Return New ArraySegment(Of T)(this, start, length)
End Function
<System.Runtime.CompilerServices.Extension>
Public Function SetValue(Of T)(this As ArraySegment(Of T), index As Integer, newValue As T) As ArraySegment(Of T)
this.Array(this.Offset + index) = newValue
Return this
'End Sub
End Function
End Module |