* arith.c (gcd): Fix semantics. If either operand is

zero, return the other operand.
(lcm): New function.

* eval.c (eval_init): Retarget registration of gcd to
variable argument gcdv function. Register lcm.

* lib.c (gcdv, lcmv): New functions.

* lib.h (gcdv, lcm, lcmv): Declared.

* txr.1: Re-document gcd with coverage of lcm.

* txr.vim: Regenerated.

1 files changed, 16 insertions, 2 deletions

diff --git a/arith.c b/arith.c
index 76066d63..7699ad11 100644
--- a/arith.c
+++ b/arith.c
@@ -1375,8 +1375,11 @@ val gcd(val anum, val bnum)
   if (!integerp(anum) || !integerp(bnum))
     goto inval;
 
-  if (zerop(anum))
-    return zero;
+  if (anum == zero)
+    return bnum;
+
+  if (bnum == zero)
+    return anum;
 
   if (fixnump(anum))
     anum = bignum(c_num(anum));
@@ -1398,6 +1401,17 @@ bad:
             anum, bnum, nao);
 }
 
+val lcm(val anum, val bnum)
+{
+  if (anum == zero || bnum == zero) {
+    return zero;
+  } else {
+    val prod = mul(anum, bnum);
+    val gcdv = gcd(anum, bnum);
+    return abso(trunc(prod, gcdv));
+  }
+}
+
 val floorf(val num)
 {
   if (integerp(num))