DIY FP - Implementing floating point math on a microcontroller without a hardware FPU
If you want to do it yourself, I'd say just do it.

I guess you wont find too many resources or tutorial because there is not much to it.

Here is an outline:


adding/subtracting:
if exponents differ too much (more than the mantissa has bits): 
just return the value with larger exponent (if this is the subtrahend: negate)

if exponents are similar: 
shift the mantissa of smaller value by difference of exponents and 
add to/subtract from other mantissa (using fixed point arithmetic)
if result is not 0: shift mantissa up until MSBit of result is 1 and decrement exponent the same amount 
multiplication/division:
multiply/divide mantissas (using fixed point arithmetic)
and add/subtract exponents