This is the fdlibm library imported from https://github.com/freebsd/freebsd Upstream code can be viewed at https://github.com/freebsd/freebsd/tree/master/lib/msun/src Each file is downloaded separately, as cloning whole repository takes so much resources. The in-tree copy is updated by running sh update.sh from within the modules/fdlibm directory. Current version: [commit b21ccf63f28a3a4692d8a31419e0a725a1b1a800 (2018-02-14T07:59:30Z)]. patches 01-14 fixes files to be usable within mozilla-central tree. See https://bugzilla.mozilla.org/show_bug.cgi?id=933257