range: Introduce range_inverse_array()

This helper reverses a list of regions within a [low, high]
span, turning original regions into holes and original
holes into actual regions, covering the whole UINT64_MAX span.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Yanghang Liu <yanghliu@redhat.com>
Reviewed-by: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

include/qemu/range.h

@@ -225,4 +225,12 @@ int range_compare(Range *a, Range *b);
 
 GList *range_list_insert(GList *list, Range *data);
 
+/*
+ * Inverse an array of sorted ranges over the [low, high] span, ie.
+ * original ranges becomes holes in the newly allocated inv_ranges
+ */
+void range_inverse_array(GList *in_ranges,
+                         GList **out_ranges,
+                         uint64_t low, uint64_t high);
+
 #endif

util/range.c

@@ -66,3 +66,58 @@ GList *range_list_insert(GList *list, Range *data)
 
     return list;
 }
+
+static inline
+GList *append_new_range(GList *list, uint64_t lob, uint64_t upb)
+{
+    Range *new = g_new0(Range, 1);
+
+    range_set_bounds(new, lob, upb);
+    return g_list_append(list, new);
+}
+
+
+void range_inverse_array(GList *in, GList **rev,
+                         uint64_t low, uint64_t high)
+{
+    Range *r, *rn;
+    GList *l = in, *out = *rev;
+
+    for (l = in; l && range_upb(l->data) < low; l = l->next) {
+        continue;
+    }
+
+    if (!l) {
+        out = append_new_range(out, low, high);
+        goto exit;
+    }
+    r = (Range *)l->data;
+
+    /* first range lob is greater than min, insert a first range */
+    if (range_lob(r) > low) {
+        out = append_new_range(out, low, MIN(range_lob(r) - 1, high));
+    }
+
+    /* insert a range inbetween each original range until we reach high */
+    for (; l->next; l = l->next) {
+        r = (Range *)l->data;
+        rn = (Range *)l->next->data;
+        if (range_lob(r) >= high) {
+            goto exit;
+        }
+        if (range_compare(r, rn)) {
+            out = append_new_range(out, range_upb(r) + 1,
+                                   MIN(range_lob(rn) - 1, high));
+        }
+    }
+
+    /* last range */
+    r = (Range *)l->data;
+
+    /* last range upb is less than max, insert a last range */
+    if (range_upb(r) <  high) {
+        out = append_new_range(out, range_upb(r) + 1, high);
+    }
+exit:
+    *rev = out;
+}