Stint (Stack-based arbitrary precision integers)

stint provides efficient and convenient N-bit integers for Nim, for arbitrary sizes of N decided at compile time with an interface similar to to int64/uint64.

In addition to basic integer operations, stint also contains primtives for modular arithmetic, endian conversion, basic I/O, bit twiddling etc.

stint integers, like their intXX/uintXX counterpart in Nim are stack-based values, meaning that they are naturally allocation-free and have value-based semantics.

import stint

func addmul(a, b, c: UInt256): UInt256 =
  a * b + c

echo addmul(u256"100000000000000000000000000000", u256"1", u256"2")

Priorities

• Portability
  • 32 and 64 bit
  • ARM/x86/x86_64 extensively tested
  • Additionally RISC-V and MIPS for open hardware and low power IoT devices.
• Speed, library is carefully tuned to produce the best assembly given the current compilers. However, the library itself does not require assembly for portability.
• No heap/dynamic allocation
• Ease of use:
  • Use traditional +, -, +=, etc operators like on native types
  • converting to and from raw byte BigInts (also called octet string in IETF specs)
  • converting to and from Hex
  • converting to and from decimal strings

Non-priorities include:

• constant-time operation (not suitable for certain kinds of cryptography out of the box)
• runtime precision

See also

• constantine - modular arithmetic and elliptic curve operations focusing on cryptography and constant-time implementation
• N2472 - _ExtInt(N) - native arbitrary precision integers for C
• stew - helpers and utilities for ordinary Nim integers (endians2, bitops2 etc)

License

Licensed and distributed under either of

• MIT license: LICENSE-MIT or http://opensource.org/licenses/MIT

or

• Apache License, Version 2.0, (LICENSE-APACHEv2 or http://www.apache.org/licenses/LICENSE-2.0)

at your option. This file may not be copied, modified, or distributed except according to those terms.