The Boost library has data types as part of multiprecision library, for types ranging from 128 to 1024 bits. #include <boost/multiprecision/cpp_int.hpp> using namespace boost::multiprecision; int128_t mySignedInt128 = -1; uint128_t myUnsignedInt128 = 2; int256_t mySignedInt256 = -3; uint256_t myUnsignedInt256 = 4; int512_t mySignedInt512 = -5; uint512_t myUnsignedInt512 = 6; int1024_t mySignedInt1024 = -7; uint1024_t myUnsignedInt1024 = … Read more
That corresponds to the long (or Int64), a 64-bit integer. Although if the number from the database happens to be small enough, and you accidentally use an Int32, etc., you’ll be fine. But the Int64 will definitely hold it. And the error you get if you use something smaller and the full size is needed? … Read more
Credits to http://moeffju.net/blog/using-bigint-columns-in-rails-migrations class CreateDemo < ActiveRecord::Migration def self.up create_table :demo, :id => false do |t| t.integer :id, :limit => 8 end end end See the option :id => false which disables the automatic creation of the id field The t.integer :id, :limit => 8 line will produce a 64 bit integer field
Current computers have 32 or 64-bit registers, so doing calculations on bytes is very inefficient. Also, computers work in binary, so using a base that is a power of 2 is more efficient. They’ll use base 232 or 264 like Mysticial said. Each computer word will store a digit of the number and they work … Read more
Big integers aren’t actually limited to 20 digits, they’re limited to the numbers that can be expressed in 64 bits (for example, the number 99,999,999,999,999,999,999 is not a valid big integer despite it being 20 digits long). The reason you have this limitation is that native format integers can be manipulated relatively fast by the … Read more
GMP can do bigint operations for both C and C++. The documentation on that site is a good introduction, if you use the C++ classes they behave almost exactly like built-in primitive types.
Not with built-in JSON.parse. You’ll need to parse it manually and treat values as string (if you want to do arithmetics with them there is bignumber.js) You can use Douglas Crockford JSON.js library as a base for your parser. EDIT2 ( 7 years after original answer ) – it might soon be possible to solve … Read more
Actually gcc will use the carry automatically if you write your code carefully… Current GCC can optimize hiWord += (loWord < loAdd); into add/adc (x86’s add-with-carry). This optimization was introduced in GCC5.3. With separate uint64_t chunks in 64-bit mode: https://godbolt.org/z/S2kGRz. And the same thing in 32-bit mode with uint32_t chunks: https://godbolt.org/z/9FC9vc (editor’s note: Of course … Read more
If you’re looking for a simple library, libtommath (from libtomcrypt) is probably what you want. If you’re looking to write a simple implementation yourself (either as a learning exercise or because you only need a very limited subset of bigint functionality and don’t want to tack on a dependency to a large library, namespace pollution, … Read more