Handle arbitrary length integers in C++

Question

Can someone tell me of a good C++ library for handling (doing operations etc...) with arbitrarily large numbers (it can be a library that handles arbitrary precision floats too, but handling integers is more important)?

Please only refer to libraries that YOU used and tell me how did you managed to set it up and pick it up, maybe with a very minimalistic example or something (basically if the mentioned library lacks good documentation provide some input of your own).

For the record I'm using Windows 7 on an x64 machine, CodeBlocks as my IDE, and the latest MinGW as the compiler.

Libraries I tried:

• vlint (not enough operations, works fine for small stuff though)

• bigint (easy to set it up, compile errors and not much documentation (from which errors might be derived))

• ttmath (seemed promising, compiled some BIG example programs and ran after some fixes because of compiling errors, incomprehensible syntax because of virtually no documentantion)

• gmp (couldn't even set it up)

p.s. Removed the 'rant part of the question' that basically explained why I'm asking something that was asked a lot of times on Stackoverflow so people would read it to the end.

--> UPDATE

So i picked an answer that wasn't a direct answer to my initial question but helped me a lot to solve this and i will post some of my findings to help other c++ newbies like me to get started working with very big numbers without struggling with libraries for days like i did in an easy step by step micro-guide.

Stuff i was using (keep this in mind to follow the guide):

• Windows 7 Ultimate x64

• Amd k10 x64 (some libraries won't work with this, others will behave differently, others are custom taylored to amd k10 so this won't only help you with the library i used but possibly with others too)

• Code::Blocks 10.05 the version without MinGW included, file name "codeblocks-10.05-setup.exe" (installed on C:\Program Files (x86)\CodeBlocks)

• MinGW packages (binutils-2.15.91-20040904-1.tar.gz gcc-core-3.4.2-20040916-1.tar.gz gcc-g++-3.4.2-20040916-1.tar.gz mingw-runtime-3.11.tar.gz w32api-3.8.tar.gz) extracted on C:\MinGW

• TTMath 0.9.2 file name "ttmath-0.9.2-src.tar.gz" unzipped and copied the folder "ttmath" to the folder "C:\CPPLibs" (which is the folder where i put my c++ libraries into)

What to do to set it all up

• Go to Code:Blocks > Settings > Compiler and Debugger (My compiler was detected automatically here. If this doesn't happen with you, on "Selected Compiler" select "GNU GCC Compiler" and click "Set as Default" then on "Toolchain Exectables" on "Compilers installation directory you can choose the installation directory of the compiler or attempt to auto-detect" and with that sorted on "C++ Compiler" select or write "mingw32-g++.exe". If this happens to you just do this, on "Selected Compiler" select "GNU GCC Compiler" and click "Set as Default").

• Without leaving "Code:Blocks > Settings > Compiler and Debugger" and with the above sorted out, go to "Search Directories" and then "Compiler" click "Add" and choose the folder where you store your libraries or where you put your "ttmath" folder (in my case C:\CPPLibs) then go to "Linker" and do the same thing.

• To start coding with the "ttmath" library you have to put this line #include <ttmath/ttmath.h> before the main function (NOTE: If you use a 64bit system you WILL get a lot of errors if you don't also put this line #define TTMATH_DONT_USE_WCHAR BEFORE this line #include <ttmath/ttmath.h>, i was struggling with this crap until i found the fix that some other guy that was also struggling found and posted on the web and it worked for me) p.s. i think it's only for 64bit systems but if you do get errors just because of including the "ttmath.h" header file it's most likely because of that.

• Declaring variables that will have big integer values has to be done like so: ttmath::UInt<n> a,b,c; where "a,b,c" are your variables and "n" is the size of the numbers you can store in the variables in this form "2^(32*n)-1" for 32bit systems and this form "2^(64*n)-1" for 64bit systems

• Assigning values to variables if you do this a = 333; (and the number in place of 333 is bigger than the "long int" standard data type on c++) it won't compile because assigning values to variables like this independently of the size you specified earlier the integer can be just as big as the the "long int" standard data type on c++ (i figured this one on my own, the hard way), also even if you use a value that is smaller and it compiles alright and then you run your program and it tries to write to this variable a bigger number than the number that the mentioned "long int" standard data type can handle, then your math is going to be wrong so watch this: to assign a value to a variable the right way you have to assign it like so a = "333"; (yes i know you are pretty much treating it as a string this way but it will do operations just fine with no problems whatsoever and if you decide to "cout" the variable it will never be an exponential or scientific notation result like you get using standard integer data types without being coupled with some 'extra statements' to display the number just right)

p.s. Using this simple rules to work with integers and this library i computed fibonacci numbers up to the 100.000th number with a simple program (that took like 3min to code) in 15 to 20 seconds and the number occupied like 3 pages so besides being a practical library once you get to know how it works (that you had virtually no help before, some samples of the ttmath website are pretty misleading, but now you do have some help) it also seems pretty efficient, i confirmed that the 100.000th number is probably right because i increased the size (the "n") from 10000 to 50000 and the number retained the size and the initial and final digits were the same. This is the source code i used, i used a VERY BIG number for the integer size just to test, i didn't actually bothered to see on what lenght the program would start do do stuff wrong but i know that the lenght of up to the 10.000th fibonacci number won't surpass the lenght that i defined because before this i made the program 'cout' every result until it got to 10.000th and it was always growing. I also checked the first numbers of the sequence before when i paused the program and i was seeing the 'digits grow' and confirmed the first fibonacci numbers of the sequence and they were correct. NOTE: This source code will only display the number of the fibonacci sequence that you want to know, it will only show you the numbers "growing" if you uncomment the commented lines.

#define TTMATH_DONT_USE_WCHAR
#include <ttmath/ttmath.h>
#include <iostream>

using namespace std;
int main () {

int fibonaccinumber;
cin >> fibonaccinumber;
cin.ignore();

ttmath::UInt<10000> fibonacci1,fibonacci2,fibonacci3;
fibonacci1 = 1;
fibonacci2 = 1;
//cout << "1. " << fibonacci1 << "\n2. " << fibonacci2 << "\n";

for(int i=3;i<=fibonaccinumber;i++)
{fibonacci3 = fibonacci1 + fibonacci2;
//   cout << i << ". " << fibonacci3 << "\n";
fibonacci1=fibonacci2;
fibonacci2=fibonacci3;}

cout << "the " << fibonaccinumber << "th fibonacci number is " << fibonacci2;

string endprog;
getline(cin,endprog);
return 0;}  

I didn't tinkered with arbitrary precision floats of this lbrary yet but when i do i will continue to expand this guide if i see that people are interested in it, thanks for all the comments and answers.

Answer 1

The official site (http://www.ttmath.org/) has samples of using integers (ttmath::Int<2> a,b,c;) and floating points (ttmath::Big<1,2> a,b,c;) both. Just treat these like high precision int/float without members and everything should be fine. If the error remains, can you post the full error message, and the lines of code that it errored on?