FEAT: new gcd native for resolving the greatest common divisor of two integers

Author: Oldes

src/core/n-math.c

@@ -927,3 +927,25 @@ enum {SINE, COSINE, TANGENT};
 
 	return R_FALSE;
 }
+
+/***********************************************************************
+**
+*/	REBNATIVE(gcd)
+/*
+//	gcd: native [
+//		{Returns greatest common divisor}
+//		a [integer!]
+//		b [integer!]
+//	]
+***********************************************************************/
+{
+	REBINT a = VAL_INT64(D_ARG(1));
+	REBINT b = VAL_INT64(D_ARG(2));
+
+	// Euclid's algorithm
+	if (a < 0) a = -a;
+	if (b < 0) b = -b;
+	if (b) while ((a %= b) && (b %= a));
+	SET_INTEGER(D_RET, a + b);
+	return R_RET;
+}

src/tests/units/integer-test.r3

@@ -60,6 +60,17 @@ Rebol [
 
 ===end-group===
 
+
+===start-group=== "gcd"
+	--test-- "gcd"
+		--assert 6 = gcd 54 24
+		--assert 6 = gcd 24 54
+		--assert 3 = gcd 0 3
+		--assert 3 = gcd 3 0
+		--assert 3 = gcd 21 -48
+===end-group===
+
+
 ===start-group=== "multiply"
 	--test-- "0 * 1"
 		i: 0