+= in C

[Steve Schlesinger]

I tried email this directly but it bounced.
Sorry (to the original poster) for the delay in answering.
Sorry to everyone else if it was aleady answered and I missed it.


In article <20039 at beta.UUCP> you write:
>To some extent, the lack of detailed knowledge
>of C is my reason for not using it. (For example: why is 'a+=b' faster
>than 'a=a+b'?  Seems to me that the two are identical and should generate
>the exact same code.)


When optimized, yes they are the same.

Without optimization consider

	a[i][j] = a[i][j] + b
vs.
	a[i][j] += b

In the second case the address a[i][j] is computed only once and reused.
This is faster both at compilation and execution times.

An optimizer would convert the first to the second.
--