subtraction between unsigned ints

[Norman Diamond]

Someone asked:

>>>Does pANSI defines the datatype of the result of subtraction
>>>between unsigned integers?  Would it be also unsigned?  Then
>>>what would be the result of subtraction of a number from a
>>>smaller number?

I answered:

>>It always has been unsigned, even in K&R days.  pANS says that the
>>result must wrap around modulo some power of 2; this was not required
>>by K&R but surely always occured.

In article <12570024 at hpclwjm.HP.COM> walter at hpclwjm.HP.COM (Walter Murray) writes:

>I think it was required by K&R.  See Appendix A, section 6.5, in the
>first edition (page 184).

That section specifies conversion from [signed] int to unsigned int.
It does not specify the result of subtraction.

Hmm, this raises a new question.  Someone who had the good fortune to
receive service from Global Engineering Documents, please kindly answer:

Does the standard specify the same conversion as K&R-1 did?  Or is this
another quiet change?  On a 1's complement machine, K&R-1 required more
computation than just a move instruction.  Do the pants impose the same
requirement?

--
-- 
Norman Diamond, Sony Corporation (diamond at ws.sony.junet)
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