Comment by dpayne

Recompiling without fastmath gives the same answer as the article "3.1415926545880506".

  mac >> clang++ -O3 -march=native main.cpp
  mac >> ./a.out
  3.1415926545880506
  total time taken is: 4.3861569999999999s

Twice as slow as the fastmath version but still faster than the go version.