This is actually pretty common. There was a time when not every CPU had a FPU and floating point operations were emulated in software if required. Or doing 64 bit integer operations on a 32 bit CPU. Or doing arbitrary precision arithmetics on todays CPUs. You do it just like in school, piece by piece, but instead of single digits you use the largest registers available. If you really like it slow you could of course also just use plain strings to represent numbers and do all math on a char by char, digit by digit basis.
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This is actually pretty common. There was a time when not every CPU had a FPU and floating point operations were emulated in software if required. Or doing 64 bit integer operations on a 32 bit CPU. Or doing arbitrary precision arithmetics on todays CPUs. You do it just like in school, piece by piece, but instead of single digits you use the largest registers available. If you really like it slow you could of course also just use plain strings to represent numbers and do all math on a char by char, digit by digit basis.