[med-svn] [python-mne] 14/353: ENH : raise warning with n_fft is not a power of 2

[Yaroslav Halchenko]

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yoh pushed a commit to tag 0.4
in repository python-mne.

commit c15907c224577a4110b1711e4a29e780e13bdf76
Author: Alexandre Gramfort <alexandre.gramfort at inria.fr>
Date:   Sat Nov 12 16:16:37 2011 -0500

    ENH : raise warning with n_fft is not a power of 2
---
 mne/filter.py | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/mne/filter.py b/mne/filter.py
index c21c05c..44dda4f 100644
--- a/mne/filter.py
+++ b/mne/filter.py
@@ -1,8 +1,33 @@
+import warnings
 import numpy as np
 from scipy import signal
 from scipy.fftpack import fft, ifft
 
 
+def is_power2(num):
+    """Test if number is a power of 2
+
+    Parameters
+    ----------
+    num : int
+        Number
+
+    Returns
+    -------
+    b : bool
+        True if is power of 2
+
+    Example
+    -------
+    >>> is_power2(2 ** 3)
+    True
+    >>> is_power2(5)
+    False
+    """
+    num = int(num)
+    return num != 0 and ((num & (num - 1)) == 0)
+
+
 def _overlap_add_filter(x, h, n_fft=None, zero_phase=True):
     """ Filter using overlap-add FFTs.
 
@@ -55,6 +80,9 @@ def _overlap_add_filter(x, h, n_fft=None, zero_phase=True):
     if n_fft <= 0:
         raise ValueError('n_fft is too short, has to be at least len(h)')
 
+    if not is_power2(n_fft):
+        warnings.warn("FFT length is not a power of 2. Can be slower.")
+
     # Filter in frequency domain
     h_fft = fft(np.r_[h, np.zeros(n_fft - n_h, dtype=h.dtype)])
 

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