First, ATLAS defines the macro `ATL_USERMM`
to the appropriate ATLAS internal kernel name. Second, it defines one
of `SREAL`, `DREAL`, `SCPLX`, `DCPLX`, according to
the data type being compiled (single precision real, double precision
real, single precision complex, double precision complex, respectively).

Similarly, ATLAS defines a macro indicating the case being
compiled, `BETA1` ( should be assumed to be 1.0), `BETA0`
( should be assumed to be 0.0), and `BETAX`
( neither zero or one, and should be handled as an input parameter).

Finally, the fixed blocking factors for each dimension are defined
`MB`, `NB`, `KB`. Note that for our L1 matmul,
`MB` = `NB` = `KB` = ; they are separated out for
support of the cleanup codes, where they can be different. ATLAS also
defines the macros `MB2`, `NB2`, `KB2`, which are simply
two times the appropriate blocking factor.