From @mcaldwelva on November 9, 2015 23:5

This line of code is overly restrictive:

if (i > n || c < 0X21 || c > 0X7E)return false;

Windows will use extended ASCII in short file names if they are present in the long file name. Based on the Wikipedia entry for FAT 8.3 file naming, something like this seems more appropriate:

if (i > n || c < 0x20 || c == 0x7F) return false;

I hope you will consider making a change along these lines in the future. Thanks!

Copied from original issue: arduino/Arduino#4121