BigNumberLib Package
Author: WaynePhillipsEA. Version: 1.0.2.0. 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
Some members give wrong results, or do not return. Each is described under its member on the BigNumber page:
- Setting IsNegative to True does not make a number negative. AssignGreatestCommonDivisor and AssignLeastCommonMultiple leave a negative operand in the same state, with its minus sign gone.
- AssignFromLong with 0 gives a zero that is flagged negative, which IsEqualTo does not find equal to a zero read from a string. AssignSquared of zero and AssignModulus with a negative divisor can give the same zero.
- AssignModularMultiplicativeInverse does not return when the modulus is odd and the value is zero or the modulus is negative.
- Overflow is not trapped: a result of more than the library holds, a little over 4096 bits, loses its high bits, with no error.
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 1.0.2.0 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.