... > That would instead be more than 512-16=496 CPUs, correct? 496 CPUs would > only require a 31-bit shift, which should be OK, but 497 would require > a 32-bit shift, which would result in sign extension. If it turns out > that sign extension is OK, then we should get in trouble at 513 CPUs, > which would result in a 33-bit shift (and is that even defined in C?). Not quite right :-) (1 << 31) is int and negative, that gets sign extended before being converted to 'unsigned long' - so has the top 33 bits set. (1 << 32) is undefined, the current x86 cpu ignore the high shift bits so it is (1 << 0). If the mask is being used to optimise a search the code might just happen to work! David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
