"softfloat": Unaltered files from SoftFloat v3c.
  http://www.jhauser.us/arithmetic/SoftFloat.html
  
  "openbsd": Unaltered files from OpenBSD 6.0. Original path is "lib/libm/src"
  "openbsd/include": Compatibility headers needed to build files from OpenBSD.
  http://www.openbsd.org
  
  Why use OpenBSD's libm? First and foremost, nearly everyone use fdlibm in a way
  or another, and OpenBSD is no exception. That being said, OpenBSD comes with a
  single-precision variant (which fdlibm itself lacks). And more interestingly,
  this variant does all its computation in single-precision (it never upgrades to
  double-precision). In our case, this is very interesting because we're doing
  single-precision computation when we better performance at the cost of accuracy,
  and in our cse our hardware has a single-precision FPU so switching to double
  can yield much lower performances.