> It's actually slightly less efficient in the caller (although obviously > memset() is going to execute faster than bitmap_set()). Partly because > x86 made some odd choices about the behaviour of an 8-bit move instruction > (it leaves the upper 24 bits intact, rather than zeroing them, so gcc > has to use a 32-bit move instruction to put 0xff into the second argument > to memset()),
Heh, I thought gcc knew and made full use of the semantics of memset, so that only the low byte matters. I suppose there might be architectures where passing -1 is slightly cheaper (at least in code size) than 255... [quick checking] indeed, on x86_64, there's no change in the generated code, but on 32 bit, gcc ends up doing 6a ff push $0xffffffff instead of 68 ff 00 00 00 push $0xff
