This blog is updated daily.
A general description is here.
By default the (arbitrary) signs of the loadings from ‘princomp()’ are chosen so the first element is non-negative.
‘configure’ works harder to set additional flags in ‘SAFE_FFLAGS’ only where necessary, and to use flags which have little or no effect on performance.
In rare circumstances it may be necessary to override the setting of ‘SAFE_FFLAGS’.