Fix string multiplication by 0 (and less than 1) to emit empty string

src/builtin.c

@@ -359,10 +359,12 @@ static jv f_multiply(jq_state *jq, jv input, jv a, jv b) {
       str = b;
       num = a;
     }
-    jv res = jv_null();
+    jv res;
     double d = jv_number_value(num);
-    int n = 0.0 < d && d < 1.0 ? 1 : d;
+    if (d < 0 || isnan(d)) {
-    if (n > 0) {
+      res = jv_null();
+    } else {
+      int n = d;
       size_t alen = jv_string_length_bytes(jv_copy(str));
       res = jv_string_empty(alen * n);
       for (; n > 0; n--) {

tests/jq.test

@@ -1286,7 +1286,11 @@ indices(", ")
 
 [.[] * "abc"]
 [-1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 3.7, 10.0]
-[null,null,null,"abc","abc","abc","abcabcabc","abcabcabcabcabcabcabcabcabcabc"]
+[null,null,"","","abc","abc","abcabcabc","abcabcabcabcabcabcabcabcabcabc"]
+
+[. * (nan,-nan)]
+"abc"
+[null,null]
 
 [.[] / ","]
 ["a, bc, def, ghij, jklmn, a,b, c,d, e,f", "a,b,c,d, e,f,g,h"]