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Re:What is your favourite C programming trick? by mansr on Friday October 14, 2011 @11:14AM (#3111471)
No. ~0 has type signed int, which on a one's complement machine is a negative zero. Converting this to an unsigned type yields zero. On a sign-magnitude machine, ~0 is -0x7fffffff (assuming 32-bit for simplicity). Conversion to unsigned 32-bit is done by adding 0x100000000, yielding 0x80000001, again not what was desired. If the variable being assigned to has a width different from that of int, things get even more interesting.
Re:What is your favourite C programming trick? by tptacek on Friday October 14, 2011 @11:20AM (#3111497)
Ah. Thanks! Is there a ones-complement or sign-magnitude architecture still in production anywhere? (I'm curious; I have no idea.)
Re:What is your favourite C programming trick? by joel4039 on Friday October 14, 2011 @12:34PM (#3111817)
As far as I know analog devices still makes some ones-complement Analog to Digital Converters. But I don't know of any modern processor that uses them.
Re:What is your favourite C programming trick? by wglb on Friday October 14, 2011 @07:35PM (#3113402)
How about ~0U?
Re:What is your favourite C programming trick? by mansr on Friday October 14, 2011 @11:01PM (#3113833)
That will only set as many bits as are in an int, which is wrong if the type of the variable you are setting is wider than int. For a long, you could of course use ~0ul, and so on for other types, but then you'd have to find and update every such assignment if the variable were ever changed to a wider type.