Is unary minus equivalent to binop minus?

Question

My C compiler gave a warning when using unary minus on an unsigned value, so I fixed the warning by doing a subtraction from 0 instead.

Now I wonder if the current code is equivalent to the original one:

uint32_t a, b; // assume b is initialized and non-zero

a =  -b   % b; // old code
a = (0-b) % b; // current code

My question is: for the same values of b will both lines of code yield the same result for a?

@juanchopanza, no not an exact duplicate because of possible integer promotion. — Jens Gustedt, Apr 24 '15 at 09:29

score 3 · Accepted Answer · answered Apr 24 '15 at 09:28

3

Usually, yes, unless on your platform uint32_t would be a narrow type. Then it would first be promoted to int and the negation would be made in that type.

answered Apr 24 '15 at 09:28

Jens Gustedt

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In which case the end result would be the same :-) – 2501 Apr 24 '15 at 09:31

Is unary minus equivalent to binop minus?

1 Answers1