Decimal floating point to binary floating point

[Dan]

I've been writing firmware for a hobby calculator project using BCD. Today I was looking at the datasheet for the ARM Cortex M4 (for the TI Tiva C Launchpad microcontroller) and was impressed to see a hardware implementation of +,-,*,/ and square root for floating point numbers in IEEE754 single precision format.

I've seen a few tutorials on how to convert decimal numbers like 8.25 to binary floating point format and I should be able to code the algorithm but I'm not sure about an algorithm for converting larger numbers like 8.25 * 10^84 to binary floating point, i.e. I'm not sure what's the best way to deal with the 10^84 part.

Now 10^84 = 2^84 * 5^84 but then you have to deal with 5^84.

I want to code an algorithm that converts decimal floating point numbers entered by the user to binary floating point numbers in order to exploit the Cortex floating point instructions.