This directory contains all code for the mpn layer of GMP.

Most subdirectories contain machine-dependent code, written in assembly or C.
The `generic' subdirectory contains default code, used when there is no
machine-dependent replacement for a particular machine.

There is one subdirectory for each ISA family.  Note that e.g., 32-bit SPARC
and 64-bit SPARC are very different ISA's, and thus cannot share any code.

A particular compile will only use code from one subdirectory, and the
`generic' subdirectory.  The ISA-specific subdirectories contain hierachies of
directories for various architecture variants and implementations; the
top-most level contains code that runs correctly on all variants.