SDCC could provide a BCD type of variables, using packed BCD structure.
This way the XCHD instruction of 8051 core would be most valuable. Of course DA A also is very useful for the decimal numbering system.

Using pBCD type in 1 byte can be stored a number 0 - 99 decimal.
This type of numbering system together with libraries for BCD calculus
give the most accurate system for decimals as known. In conjuction with
fractions, math is accurate even for 1/3.

In C# there is a class of numbers that occupies 128bits to store financial
data in decimal system with many digits after the decimal point. Such a number type uses part of its storage for sign, NaN, +Infinite, -Infinite, +0, -0.
A lightweight method for packedBCD in 8051 could be provided as addon
feature with SDCC.