add checking of numeric indices to an array to see if they can reasonably be considered integers. Avoid undefined behaviour if out of bounds

jv.c

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdarg.h>
+#include <limits.h>
 
 #include "jv_alloc.h"
 #include "jv.h"
@@ -140,6 +141,17 @@ double jv_number_value(jv j) {
   return j.u.number;
 }
 
+int jv_is_integer(jv j){
+  if(jv_get_kind(j) != JV_KIND_NUMBER){
+    return 0;
+  }
+  double x = jv_number_value(j);
+  if(x != x || x > INT_MAX || x < INT_MIN){
+    return 0;
+  }
+
+  return x == (int)x;
+}
 
 /*
  * Arrays (internal helpers)

jv.h

@@ -60,6 +60,7 @@ jv jv_bool(int);
 
 jv jv_number(double);
 double jv_number_value(jv);
+int jv_is_integer(jv);
 
 jv jv_array();
 jv jv_array_sized(int);

jv_aux.c

@@ -51,10 +51,15 @@ jv jv_get(jv t, jv k) {
       v = jv_null();
     }
   } else if (jv_get_kind(t) == JV_KIND_ARRAY && jv_get_kind(k) == JV_KIND_NUMBER) {
-    // FIXME: don't do lookup for noninteger index
-    v = jv_array_get(t, (int)jv_number_value(k));
-    if (!jv_is_valid(v)) {
-      jv_free(v);
+    if(jv_is_integer(k)){
+      v = jv_array_get(t, (int)jv_number_value(k));
+      if (!jv_is_valid(v)) {
+        jv_free(v);
+        v = jv_null();
+      }
+    } else {
+      jv_free(t);
+      jv_free(k);
       v = jv_null();
     }
   } else if (jv_get_kind(t) == JV_KIND_ARRAY && jv_get_kind(k) == JV_KIND_OBJECT) {

tests/all.test

@@ -718,3 +718,7 @@ map(has(2))
 keys
 [42,3,35]
 [0,1,2]
+
+[][.]
+1000000000000000000
+null