快速傅里叶变换模块VB版.docVIP

‘kkfft.bas，VB版快速傅里叶变换模块，翻译自徐世良的“C 语言常用算法程序集”，供vb用户免费使用 ‘yangwqcumt,2012.04 ‘---------------------------------------------------------------------------------- ‘模块说明： ‘Pr(),pr(),分别是输入序列的实部与虚部； ‘Fr(),fi()分别是输出序列的实部与虚部； ‘以上数组的长度都是n，而且n等于2的k次方，n=2k ‘L为0时做正变换，为1时做反变换 ‘--------------------------请参考徐教授的著作--------------------------- Public Sub kkfft(ByRef pr() As Double, _ ByRef pi() As Double, _ ByRef fr() As Double, _ ByRef fi() As Double, _ ByVal n As Integer, _ ByVal k As Integer, ByVal L As Integer) Dim it As Integer Dim m As Integer Dim iis As Integer Dim i As Integer Dim j As Integer Dim nv As Integer Dim l0 As Integer Dim p, q, s, vr, vi, poddr, poddi As Double For it = 0 To n - 1 m = it iis = 0 For i = 0 To k - 1 j = Int(m / 2) iis = 2 * iis + (m - 2 * j) m = j Next fr(it) = pr(iis) fi(it) = pi(iis) Next pr(0) = 1# pi(0) = 0# p = 6.283185306 / (1# * n) pr(1) = Cos(p) pi(1) = -Sin(p) If l 0 Then pi(1) = -pi(1) For i = 2 To n - 1 p = pr(i - 1) * pr(1) q = pi(i - 1) * pi(1) s = (pr(i - 1) + pi(i - 1)) * (pr(1) + pi(1)) pr(i) = p - q pi(i) = s - p - q Next For it = 0 To n - 2 Step 2 vr = fr(it) vi = fi(it) fr(it) = vr + fr(it + 1) fi(it) = vi + fi(it + 1) fr(it + 1) = vr - fr(it + 1) fi(it + 1) = vi - fi(it + 1) Next m = n / 2 nv = 2 For l0 = k - 2 To 0 Step -1 m = m / 2: nv = 2 * nv For it = 0 To (m - 1) * nv Step nv For j = 0 To (nv / 2) - 1 p = pr(m * j) * fr(it + j + nv / 2) q = pi(m * j) * fi(it + j + nv / 2) s = pr(m * j) + pi(m * j) s = s * (fr(it + j + nv / 2) + fi(it + j + nv / 2)) poddr = p - q poddi = s - p - q fr(it + j + n