BigNumberLib Package

Author: WaynePhillipsEA. Version: 1.0.4.0. On GitHub: libtom/tomsfastmath, the C library that the package wraps.

The BigNumberLib contributed package provides arbitrary-precision signed integer arithmetic for twinBASIC. Its one class, BigNumber, holds an integer of up to 4096 bits. The arithmetic is done by version 0.13.1 of the TomsFastMath (libtfm) C library, which the package links as a static library, one build for 32-bit programs and one for 64-bit programs.

A number is set and read as a string in decimal, hexadecimal, octal or binary, or is set from a Long. The class adds, subtracts, multiplies, divides and squares; takes a remainder, also of a sum, a difference, a product or a square; finds a modular inverse, a greatest common divisor and a least common multiple; shifts; and compares.

Warning 1.0.4.0

Some members give wrong results with no error, or do not return. The BigNumber page describes each:

• AssignLeastCommonMultiple of two zeros leaves the number as it was.
• Overflow is trapped by some members only. A value of more bits than the library holds, a little over 4096, gives a wrong result with no error in subtraction, squaring, the modular operations, some multiplications, and ValueOctal and ValueBinary. A remainder of a number within one word of what the library holds does not return.

Classes

• BigNumber – arbitrary-precision signed integer backed by the TomsFastMath (libtfm) C library, supporting numbers up to 4096 bits.

Test code

The package also contains BigNumberTests, a module with one Sub, RunAllTests, which runs the RunTests Sub of 22 test modules, one for each operation and each string conversion (Addition, Divide, Modulus, ShiftLeft, ValueHex, Comparisons and so on). Together they make 777 checks with Debug.Assert, which a built program skips. Run in the IDE, version 1.0.4.0 passes all of them. These modules have no pages of their own here.

BigNumber also declares a structure type, fp_int, which holds the number for the library, and a program does not use it.

Test cases

The notes and warnings of this section are checked by the test cases in BigNumberLib-tests.twinproj, a twinBASIC project. It uses BigNumberLib as a linked package: put the package’s .twinpack in %APPDATA%\twinBASIC\packages, then run the project, and each case prints whether it passes.