Decimal Type for Phobos

This code is a work in progress for a new type Decimal that follows the "General Decimal Arithmetic Specification" http://speleotrove.com/decimal/decarith.html

Example

import stdxdecimal;

void main()
{
    auto d1 = decimal("1.23");
    auto d2 = decimal("1.23E-4");
    auto d3 = decimal("1.23E4");

    assert(d1.toString() == "1.23");
    assert(d2.toString() == "0.000123");
    assert(d3.toString() == "12300");

    auto d4 = d1 + d2;
    assert(d4.toString() == "1.230123");

    auto d5 = d3 - d1;
    assert(d5.toString() == "12298.87");

    auto d6 = decimal!(HighPrecision)("1.000000000000000000000000000000000000000000000000001");
    auto d7 = decimal!(HighPrecision)("1E-51");
    auto d8 = d6 + d7;
    assert(d8.toString() == "1.000000000000000000000000000000000000000000000000002");
}

Current Features

Feature	Implemented
Construction from strings/string-like ranges	✓
Construction from number types	✓
To decimal string	✓
To scientific string	❌
To engineering string	❌
All rounding types	❌
Overflow/Underflow Behavior	❌
Subnormal Behavior	❌
Clamping Behavior	❌
Equals	✓
toHash	❌
Compare	✓
Addition	✓
Subtraction	✓
Multiply	✓
Divide	✓
Divide-Integer	❌
Modulo	❌
DivMod	❌
opOpAssign +,-,*,/,^^	❌
Unary +,-,++,--	✓
opCast int,real,bool	✓
abs	✓
ln	❌
log10	❌
exp	❌
sqrt	❌
power	❌
reduce	❌

Current Performance

Run on a 15", 2015 Macbook Pro, (rounded to the nearest ms; test values purposely avoid rounding, which is the slowest part by far)

Test	BigInt	Decimal (P = 16)	Decimal (P = 64)	Python Decimal	Python Decimal (64 Digits)
Addition (n = 5M)	594 ms	3,383 ms	6,414 ms	799 ms	741 ms
Subtraction (n = 5M)	494 ms	3,092 ms	6,028 ms	800 ms	830 ms
Multiplication (n = 5M)	156 ms	448 ms	1,797 ms	695 ms	1541 ms
Division (n = 1M)	207 ms	5,261 ms	18,283 ms	215 ms	416 ms

Run It Yourself

D: ldc2 -O -release bench.d source/stdxdecimal/package.d && ./bench

Python:

import timeit

timeit.timeit("c = a + b", setup="from decimal import Decimal; a = Decimal(10000.12); b = Decimal(5000000); c = None", number=5000000)
timeit.timeit("c = a + b", setup="from decimal import Decimal; a = Decimal(1000000000000000000000000000000000000000000000000000000000000000); b = Decimal(5000000000000000000000000000000000000000000000000000000000000000); c = None", number=5000000)
timeit.timeit("c = a - b", setup="from decimal import Decimal; a = Decimal(10000.12); b = Decimal(5000000); c = None", number=5000000)
timeit.timeit("c = a - b", setup="from decimal import Decimal; a = Decimal('10000000000000000000000000000000000000000000000000000000000000.12'); b = Decimal('5000000000000000000000000000000000000000000000000000000000000000'); c = None", number=5000000)
timeit.timeit("c = a * b", setup="from decimal import Decimal; a = Decimal(10000.12); b = Decimal(5000000); c = None", number=5000000)
timeit.timeit("c = a * b", setup="from decimal import Decimal; a = Decimal('10000000000000000000000000000000000000000000000000000000000000.12'); b = Decimal('5000000000000000000000000000000000000000000000000000000000000000'); c = None", number=5000000)
timeit.timeit("c = a / b", setup="from decimal import Decimal; a = Decimal(10000.12); b = Decimal(5000000); c = None", number=1000000)
timeit.timeit("c = a / b", setup="from decimal import Decimal; a = Decimal('10000000000000000000000000000000000000000000000000000000000000.12'); b = Decimal('5000000000000000000000000000000000000000000000000000000000000000'); c = None", number=1000000)