This gives you an alternate software floating point implementation that doesn't
rely on compiler intrinsics or arch-specific behavior. On
certain architectures, this library also provides an implementation
for certain missing compiler intrinsics (e.g. __floatunditf and
__fixunstfdi on AArch64).
The way this is put together, the Softfloat-3d/ directory contains a completely unmodified Release 3d of the Berkeley SoftFloat package. This should make you feel better about bugs introduced in the UEFI packaging, but also allow reasonably simple updates.
SoftFloatLib.inf is derived from the SoftFloat-3d/build/Linux-x86_64-GCC
configuration. Include/SoftFloatLib.h is the header
file, and is derived from SoftFloat-3d/source/include/softfloat.h.