CODEWITHSUNDEEP
cgcc
Vishwajith.K
Vishwajith.K

Reputation: 139

Is there a gcc function to add two large numbers for C?

I am trying to add two numbers in C. My code is

#define type unsigned
type add(type a, type b) {
    return a + b;
}

Code corresponding to above code in assembly makes use of a single add instruction (https://godbolt.org/ & ARM GCC 8.3.1). However when I changed the type to unsigned long long, code was bit obfuscated to understand; But, I believe it makes use of some ldm and then asks hardware to add complete vectors (or arrays). Similarly my next question was: is it possible to add two numbers where digits count in each number will be in the order of 1000s? It isn't hard to design a function and make it work, and I found many codes on internet which do this. But, I think compiler writes better code than us,

Upvotes: 0

Views: 193

Answers (1)

Ray Hamel
Ray Hamel

Reputation: 1309

No, there is no compiler support in GCC for arbitrary-precision arithmetic. You would need to use a library like GMP. If you can use C++ instead of C, you can get a more "natural" API (with arithmetic operators, etc.) by using a library like Boost Multiprecision.

GCC does support, as an extension, the types __int128 and unsigned __int128, which can be used like any other integral type, but these only provide capacity for 38 decimal digits.

Edit: Also, as an aside, don't use macros (like #define type unsigned) to rename types. Instead this should be written with the typedef keyword like so: typedef unsigned type;

Upvotes: 3

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