FEAT: new lcm native for resolving the least common multiple of two…

… integers
Oldes · Dec 10, 2021 · 53b04bd · 53b04bd
1 parent 12794b3
commit 53b04bd
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Showing 3 changed files with 55 additions and 14 deletions.
diff --git a/src/core/n-math.c b/src/core/n-math.c
@@ -933,19 +933,28 @@ enum {SINE, COSINE, TANGENT};
 */	REBNATIVE(gcd)
 /*
 //	gcd: native [
-//		{Returns greatest common divisor}
+//		{Returns the greatest common divisor}
 //		a [integer!]
 //		b [integer!]
 //	]
 ***********************************************************************/
 {
-	REBINT a = VAL_INT64(D_ARG(1));
-	REBINT b = VAL_INT64(D_ARG(2));
+	SET_INTEGER(D_RET, Gcd(VAL_INT64(D_ARG(1)), VAL_INT64(D_ARG(2))));
+	return R_RET;
+}
 
-	// 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);
+/***********************************************************************
+**
+*/	REBNATIVE(lcm)
+/*
+//	lcm: native [
+//		{Returns the least common multiple}
+//		a [integer!]
+//		b [integer!]
+//	]
+***********************************************************************/
+{
+	SET_INTEGER(D_RET, Lcm(VAL_INT64(D_ARG(1)), VAL_INT64(D_ARG(2))));
 	return R_RET;
 }
+
diff --git a/src/core/t-integer.c b/src/core/t-integer.c
@@ -43,6 +43,31 @@
 	return (VAL_INT64(a) > VAL_INT64(b));
 }
 
+/***********************************************************************
+**
+*/	REBINT Gcd(REBINT a, REBINT b)
+/*
+**	Greatest common divisor (Euclid's algorithm)
+**
+***********************************************************************/
+{
+	if (a < 0) a = -a;
+	if (b < 0) b = -b;
+	if (b) while ((a %= b) && (b %= a));
+	return a + b;
+}
+
+/***********************************************************************
+**
+*/	REBINT Lcm(REBINT a, REBINT b)
+/*
+**	Least common multiple
+***********************************************************************/
+{
+	if (a == 0 && b == 0) return 0;
+	return a / Gcd(a, b) * b;
+}
+
 
 /***********************************************************************
 **

diff --git a/src/tests/units/integer-test.r3 b/src/tests/units/integer-test.r3
@@ -61,13 +61,20 @@ Rebol [
 ===end-group===
 
 
-===start-group=== "gcd"
+===start-group=== "gcd/lcm"
 	--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
+		--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
+	--test-- "lcm"
+		--assert 36 = lcm 12 18
+		--assert 36 = lcm 18 12
+		--assert  0 = lcm 0 1
+		--assert  0 = lcm 1 0
+		--assert  0 = lcm 0 0
+
 ===end-group===