[Numpy-svn] r3532 - trunk/numpy/lib

[numpy-svn at scipy.org]

Author: oliphant
Date: 2007-02-01 18:47:34 -0600 (Thu, 01 Feb 2007)
New Revision: 3532

Modified:
   trunk/numpy/lib/utils.py
Log:
Add memory_bounds and may_share_memory functions to numpy.

Modified: trunk/numpy/lib/utils.py
===================================================================
--- trunk/numpy/lib/utils.py	2007-02-01 21:14:12 UTC (rev 3531)
+++ trunk/numpy/lib/utils.py	2007-02-02 00:47:34 UTC (rev 3532)
@@ -7,7 +7,8 @@
 
 __all__ = ['issubclass_', 'get_numpy_include', 'issubsctype',
            'issubdtype', 'deprecate', 'get_numarray_include',
-           'get_include', 'info', 'source', 'who']
+           'get_include', 'info', 'source', 'who',
+           'memory_bounds', 'may_share_memory']
 
 def issubclass_(arg1, arg2):
     try:
@@ -101,6 +102,56 @@
 get_numpy_include = deprecate(get_include, 'get_numpy_include', 'get_include')
 
 
+#--------------------------------------------
+# Determine if two arrays can share memory
+#--------------------------------------------
+
+def memory_bounds(a):
+    """(low, high) are pointers to the end-points of an array
+
+    low is the first byte
+    high is just *past* the last byte
+
+    The array provided must conform to the Python-side of the array interface
+    """
+    ai = a.__array_interface__
+    a_data = ai['data'][0]
+    astrides = ai['strides']
+    ashape = ai['shape']
+    nd_a = len(ashape)
+    bytes_a = int(ai['typestr'][2:])
+
+    # a_low points to first element of array
+    # a_high points to last element of the array
+
+    a_low = a_high = a_data
+    if astrides is None: # contiguous case
+        a_high += product(ashape, dtype=int)*bytes_a
+    else:
+        for shape, stride in zip(ashape, astrides):
+            if stride < 0:
+                a_low += (shape-1)*stride
+            else:
+                a_high += (shape-1)*stride
+        a_high += bytes_a
+    return a_low, a_high
+    
+
+def may_share_memory(a, b):
+    """Determine if two arrays can share memory
+
+    The memory-bounds of a and b are computed.  If they overlap then
+    this function returns True.  Otherwise, it returns False.
+
+    A return of True does not necessarily mean that the two arrays
+    share any element.  It just means that they *might*.
+    """
+    a_low, a_high = memory_bounds(a)
+    b_low, b_high = memory_bounds(b)
+    if b_low >= a_high or a_low >= b_high:
+        return False
+    return True
+
 #-----------------------------------------------------------------------------
 # Function for output and information on the variables used.
 #-----------------------------------------------------------------------------