Hey dude,
I need some code to do some big math.
Like 12345678901234567890 x 987654321987654321
Must be in C and must be documented correctly.
Has anybody got some sourcecode?
Respect.
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Define "big". As in "how many bits does the biggest number that will every occur have".
That would amount to multiplying two 64-bit integers to get a 128-bit result. Since the compiler can natively work with 64-bit integers, this means four multiplications, some additions, and some overflow checking. Unfortunately, the latter is much easier (since it's pretty much automatic) in assembly than in C (where it requires extra checks).
Please specify your requirements more clearly. What's the bit width of the numbers you're working with, which arithmetic operations do you require, etc.