✨ feat(Integer): Add parity testing methods.

Author: make-github-pseudonymous-again

src/Integer.js

@@ -370,6 +370,20 @@ export class Integer {
 		return !this.iszero();
 	}
 
+	parity ( ) {
+		// TODO optimize this, there is a much faster way to test for parity
+		// when the base is a multiple of two
+		return this.modn(2) ;
+	}
+
+	iseven ( ) {
+		return this.parity().iszero() ;
+	}
+
+	isodd ( ) {
+		return !this.iseven() ;
+	}
+
 	bin ( ) {
 		return this.toString( 2 ) ;
 	}

test/src/Integer/parity.js

@@ -0,0 +1,37 @@
+import test from 'ava' ;
+import { range } from '@aureooms/js-itertools' ;
+
+import { ZZ } from '../../../src' ;
+
+function even ( t , x ) {
+	t.true(x.iseven());
+	t.false(x.isodd());
+}
+
+even.title = ( providedTitle , x ) => `parity: ${x.toString()} is even` ;
+
+function odd ( t , x ) {
+	t.true(x.isodd());
+	t.false(x.iseven());
+}
+
+odd.title = ( providedTitle , x ) => `parity: ${x.toString()} is odd` ;
+
+test( odd , ZZ.from('123456789') ) ;
+test( odd , ZZ.from('987654321') ) ;
+test( even , ZZ.from('9876543210') ) ;
+
+test( odd , ZZ.from('ff', 16) ) ;
+
+test( even , ZZ.from(2).pow(1234) ) ;
+test( odd , ZZ.from(2).pow(1234).subn(1) ) ;
+
+const N = 100 ;
+let x = ZZ.from(-N);
+
+for ( const i of range(N) ) {
+	test( even , x ) ;
+	x = x.addn(1) ;
+	test( odd , x ) ;
+	x = x.addn(1) ;
+}