Just skimmed this link and the linked ‘dtoa.c’ in the comments led me on a path of discovery…
First: Whoa, 6202 lines of code for this
Then trying to find out more: https://stackoverflow.com/questions/3173056/why-does-dtoa-c-contain-so-much-code
Then I found the changelog: http://www.netlib.org/fp/changes
And it went from June 1991 (where this file might not even have been brand new) to the last update in April of 2018.