Many cost-sensitive ARM Cortex-M devices like the M0+ do not have a hardware floating point unit, and some like the M4 only has an optional single-precision floating point unit (FPU). As outlined in “Be aware: Floating Point Operations on ARM Cortex-M4F“, using floating point operations without a hardware unit can be costly.

Erich Styger suggests looking at the disassembly for sure will tell you if the hardware is handling the float or double operation or not.

To find out if a binary (object file, ELF/Dwarf file) is using hardware or software for the floating point operation, the GNU readelf utility can dump the necessary information. This is especially helpful for checking binaries which I do not build myself.

The only caveat is that readelf will not tell you if floating point data types are used or not: for this I still need to produce disassembly files and grep for things like __aeabi_dmul.

See more in the blog post here.