low level optimization

[Jim Giles]

> [...]
> The C standard doesn't say Thou Must Compile Separately.  [...]

No.  As far as I know, it doesn't use the word "Thou" at all.
The standard _does_ say:

    A C program need not all be translated at the same time.  The
    text of a program is kept in units called _source_files_ in 
    this standard, and previously translated files may be preserved 
    individually or in libraries.  The separate files of a program 
    communicate by calls to functions whose identifiers have external
    linkage, and by manipulation of objects whose identifiers have
    external linkage.  Translated files may be linked with previously
    translated libraries to produce an executable program.

Note: the standard specifically says that files may be compiled
in any order and that the only standard communication between files
is through external variables and functions.

J. Giles