快速傅里叶变换模块VB版.doc

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=2kl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 + nv / 2) = fr(it + j) - poddr fi(it + j + nv / 2) = fi(it + j) - poddi fr(it + j) = fr(it + j) + poddr fi(it + j) = fi(it + j) + poddi next next next if l 0 then for i