kmill

See https://codegolf.stackexchange.com/a/203682/78112

This is a description of Anders Kaseorg's solution to the code golf problem of making a program in FRACTRAN
that detects whether or not the Collatz sequence starting from the given number eventually reaches 1.

FRACTRAN programs can be thought of as being a list of chemical reactions with no catalysts (chemical
species that appear as both reagents and products).  Given a fraction c/d, the prime factors present
in d (with multiplicity) are the reagent species, and the prime factors present in c (with
multiplicity) are the product species.  Since fractions are reduced, a species is only ever either a
reagent or a product in a given reaction.

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD