Making a C library for arbitrary precision numbers
Austin Z. Henley always wanted to know how bignum libraries work, re. performing math functions on arbitrary size numbers.
I had an initial theory of how bignums work: treat numbers as strings and manually perform arithmetic on the digits as you would on a piece of paper.
It is necessary to compare numbers, like a > b or a == b. We will implement a comparison function to handle greater than, less than, and equal to.
The add function will work the same as you learned in grade school. Start with the least significant digits, add them, carry the 1 if necessary, and repeat for the next column.
Following a similar pattern as addition, multiplication won’t be that difficult to implement. It too will use a grade school algorithm: multiply each digit of the first number by each digit of the second number, and then add all the results together.
You can read more in-depth in the post here and the code can be found on GitHub.
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