Thank you for pointing me to all the prior work on this!
I am surprised how complex the issue seems to be. I assumed there might be an elegant solution, but the problem seems to be a lot harder than I thought.
See also the code in LLVM Flang for binary/decimal conversions. Minimal-digit decimals don’t come up in Fortran as often as other languages, but I use them when allowed by the output format. Interestingly, the last digit of a minimal decimal conversion is often irrelevant, so long as it exists.
I am surprised how complex the issue seems to be. I assumed there might be an elegant solution, but the problem seems to be a lot harder than I thought.