Well, given the comments at the top:
// Contributed by Mark C. Lewis.
// Modified slightly by Chad Whipkey.
// Converted from Java to C++ and added SSE support by Branimir Maksimovic.
// Converted from C++ to C by Alexey Medvedchikov.
// Modified by Jeremy Zerfas.
It sounds like no-one bothered to actually write a from-scratch version of many of these things :)
