better entropy estimation

skeletons/BOOLEAN.c

@@ -415,7 +415,19 @@ BOOLEAN_random_fill(const asn_TYPE_descriptor_t *td, void **sptr,
         }
     }
 
-    /* Simulate booleans that are sloppily set */
-    *st = asn_random_between(0, 1) ? asn_random_between(1, 0x7fffffff) : 0;
+    /* Simulate booleans that are sloppily set and biased. */
+    switch(asn_random_between(0, 7)) {
+    case 0:
+    case 1:
+    case 2:
+        *st = 0; break;
+    case 3: *st = -1; break;
+    case 4: *st = 1; break;
+    case 5: *st = INT_MIN; break;
+    case 6: *st = INT_MAX; break;
+    default:
+        *st = asn_random_between(INT_MIN, INT_MAX);
+        break;
+    }
     return result_ok;
 }

skeletons/asn_random_fill.c

@@ -20,10 +20,37 @@ asn_random_fill(const struct asn_TYPE_descriptor_s *td, void **struct_ptr,
     }
 }
 
+static uintmax_t
+asn__intmax_range(intmax_t lb, intmax_t ub) {
+    assert(lb <= ub);
+    if((ub < 0) == (lb < 0)) {
+        return ub - lb;
+    } else if(lb < 0) {
+        return 1 + ((uintmax_t)ub + (uintmax_t)-(lb + 1));
+    } else {
+        assert(!"Unreachable");
+        return 0;
+    }
+}
+
 intmax_t
-asn_random_between(intmax_t a, intmax_t b) {
-    assert(a <= b);
-    assert((b-a) < RAND_MAX);
-    if(a == b) return a;
-    return a + (random() % (b - a + 1));
+asn_random_between(intmax_t lb, intmax_t rb) {
+    if(lb == rb) {
+        return 0;
+    } else {
+        const uintmax_t intmax_max = ((~(uintmax_t)0) >> 1);
+        uintmax_t range = asn__intmax_range(lb, rb);
+        uintmax_t value = 0;
+        uintmax_t got_entropy = 0;
+
+        assert(RAND_MAX > 0xffffff);    /* Seen 7ffffffd! */
+        assert(range < intmax_max);
+
+        for(; got_entropy < range;) {
+            got_entropy = (got_entropy << 24) | 0xffffff;
+            value = (value << 24) | (random() % 0xffffff);
+        }
+
+        return lb + (intmax_t)(value % (range + 1));
+    }
 }