Re: [avr-gcc-list] Code Optimisation question re: volatile

[Matthew Arcus]

On Friday 23 July 2004 12:15 pm, D. Daniel McGlothin wrote:
> See Dennis Ritchie's C Reference Manual (May 1975)
> http://cm.bell-labs.com/cm/cs/who/dmr/cman.pdf, bottom of page 8.
>
> See Eric Huss's 1997 The C Library Reference Guide
> http://www.acm.uiuc.edu/webmonkeys/book/c_guide/ section 1.5.5.
>
> The two references differ as to the arrangement of the assignment and
> operator tokens.

Old C did have:

a =+ 10;

etc. but you had to be _very careful_ not to write eg.

a=&b;

where you meant:

a = &b;

(which is why it got changed I guess).

> In brief,
>
> pwm_state ^= _b00000011
>
> 'expands' to
>
> pwm_state = pwm_state  ^ _b00000011

but, eg:

*p++ ^= 0xaa;

doesn't expand to:

*p++ = *p++ ^ 0xaa;

Matthew.