This fixes a couple of items when converting small numbers. Seems to be a bug in fcvtf, which this is a workaround. One issue is with trailing zeros, other is with rounding. See this post for some examples.

https://forum.pjrc.com/threads/1227-Teensy3-alternative-for-dtostrf()?p=104967&viewfull=1#post104967

Per forum
https://forum.pjrc.com/threads/1227-Teensy3-alternative-for-dtostrf()?p=86671&viewfull=1#post86671

or, alternativly one could write size_t strlen(const char *s) {return __builtin_strlen(s);} to use the gcc-builtin function.
I think, both are faster than the bytewise search.