SuperKISS64 is an extremely long period (more than 10^397524) pseudorandom number generator by George Marsaglia, from http://forums.silverfrost.com/viewtopic.php?t=1480 (named SUPRKISS64.c by Marsaglia) posted 2009-11-22, modified and ported to Go by Ron Charlton 2021-06-03.
For math only see https://www.thecodingforums.com/threads/superkiss-for-32-and-64-bit-rngs-in-both-c-and-fortran.706893/
SuperKISS64 may be wrapped by math/rand.New; it implements math/rand Source and Source64. It also implements an io.Reader.
cryptosource.go is used only to initialize SuperKISS64. It doesn't make SuperKISS64 cryptographically secure. cryptosource.go may be used independent of SuperKISS64 if desired. It too implements math/rand Source, Source64 and io.Reader, and may be wrapped by math/rand.New.