I currently think the C compiler vendors have gone too far with this. Although the specification says this behaviour is undefined in practice I used to map the

I currently think the C compiler vendors have gone too far with this. Although the specification says this behaviour is undefined in practice I used to map the undefined portion to being whatever my hardware did, not whatever the compiler felt like this week. This ruins the C as a portable assembler use case and means if I was doing this sort of work I'd probably write these sort of routines in assembler rather than trying to fight with versions of C compiler.