Re: Thumb2 code size improvements

On 9/10/2010 2:17 AM, Dave Martin wrote:

(int)((unsigned)c << 28) >> 28

is invalid C, because the result of the unsigned->signed cast (needed to get arithmetic right shift) is undefined if the argument is > INT_MAX.

True, but undefined-ness (or, in this case, implementation-defined-ness, IIRC) helps the compiler; it's free to do as it wants. So, this is no excuse for the compiler generating slow code. (In particular, the compiler needn't generate a test to see whether the argument is greater than INT_MAX.)