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I’d like to write a deadsimple bignum class using a series of (unsigned) integers. I can loosely see how addition and subtraction would work, but division and multiplication is another story. I know 32-bit compilers can emuate 64-bit int’s by splitting the int64 in two int32’s. I’m looking for an efficient method to do that.
I’d like to have C++ code, not assembly. Speed is no primary concern, but the most efficient solution without assemble is always nice to have.
Perhaps this can serve as a starting point. It implements up to 2,048-bit unsigned integers, using a base-65,536 representation. This means each digit fits in 16 bits, and we can trivially detect overflow (even when multiplying) by simply using 32 bits for the results.
This is C code however, but should be trivial to port to C++, or just use as an inspiration. It’s very much optimized for readability rather than speed since this is not exactly the kind of stuff I’m good at. 🙂