RE: [avr-gcc-list] Inconsisten behaviour of switch statement

[Schwichtenberg, Knut]

Hi, 

> -----Original Message-----
> From: Eric Weddington [mailto:address@hidden 
> Sent: Monday, March 26, 2007 2:46 PM
> To: Schwichtenberg, Knut; address@hidden
> Subject: RE: [avr-gcc-list] Inconsisten behaviour of switch statement
> 
> The compiler has heuristics that decide when to compile a 
> switch statement
> into an if-else-if structure, or as a table jump. If you do 
> not like the
> output that it produces, it would be better if you coded your 
> algorithm as a
> dispatch table (array of pointers to functions). This gives 
> you more control
> as to how the compiler will transform the C into assembly.

Eric, the point is not that I don't like the output, but the case to be
selected should be deterministic. I always thought that a switch
statement would lead to identical results if the input value is
identical. This is currently not true. The table jump for a volatile
variable is identical to an if-then-else structure of a non-volatile
variable and the current if-then-else implementation for a volatile
variable can not be simulated by a table jump. 

> Have you tried typecasting all of the case
> integer constants to uint8_t? Perhaps that will have the 
> desired effect.
Not yet, I've tried to typecast the switch-Variable, but that did not
help. Therefore I'll try your idea.

Thanks

Knut