Why does std.intrinsic contain nothrow?

[Trass3r]

Right at the beginning of the file there is:

module std.intrinsic;

nothrow:

Nevertheless some functions are

pure nothrow int bsf(uint v);

some not:

int btc(uint *p, uint bitnum);

So either those nothrows are obsolete or the nothrow: is a mistake, right?