On 12/10/2011 10:46, David Cournapeau wrote: > On Wed, Oct 12, 2011 at 9:18 AM, "V. Armando Solé" wrote: >> From a pure user perspective, I would not expect the abs function to >> return a negative number. Returning +127 plus a warning the first time >> that happens seems to me a good compromise. > I guess the question is what's the common context to use small > integers in the first place. If it is to save memory, then upcasting > may not be the best solution. I may be wrong, but if you decide to use > those types in the first place, you need to know about overflows. Abs > is just one of them (dividing by -1 is another, although this one > actually raises an exception). > > Detecting it may be costly, but this would need benchmarking. > > That being said, without context, I don't find 127 a better solution than > -128.
Well that choice is just based on getting the closest positive number to the true value (128). The context can be anything, for instance you could be using a look up table based on the result of an integer operation ... In terms of cost, it would imply to evaluate the cost of something like: a = abs(x); if (a < 0) {a -= MIN_INT;} return a; Basically is the cost of the evaluation of an if condition since the content of the block (with or without warning) will bot be executed very often. I find that even raising an exception is better than returning a negative number as result of the abs function. Anyways, I have just tested numpy.array([129], dtype=numpy.int8) and I have got the array as [-127] when I was expecting a sort of unsafe cast error/warning. I guess I will just stop here. In any case, I am very grateful to the mailing list and the original poster for exposing this behavior so that I can keep it in mind. Best regards, Armando _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion