[Numpy-discussion] Binary ufuncs: minimum

Chris.Barker Chris.Barker@noaa....
Wed May 28 02:08:32 CDT 2008


Keith Goodman wrote:
>> Interestingly, MATLAB (v7.5.0) takes a different approach:
>> ans =
>>  127    1
>>>> -A
>> ans =
>>  127   -1

can anyone explain that? -- just curious.

Charles R Harris wrote:
> We could simply define the range of int8 as [-127,127], but that is 
> somewhat problematical also.

That would be nice, but probably a pain to do and could be a serious 
performance hit. And would no longer match hardware/C standards.

Charles R Harris wrote:
> I disagree. By definition, abs() >= 0 always.

and 127 + 1 = 128

This is hardware integer math. It has it's own definition, and 
apparently abs(-128) = -128.

> unsigned return will cause problems is in the augmented assignments,

well, could folks end up with inadvertent upcasting in mixed operations, 
also?

a = np.array(..., dtype=np.int8)
b = np.array(..., dtype=np.int8)

a = abs(a)

c = a + b  # or b + a

what type is c?

by the way, are you proposing that abs() always returns a unsigned 
integer type?

-Chris





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