Add a search_atleast operation.

[gnulib.git] / lib / gl_array_oset.c

diff --git a/lib/gl_array_oset.c b/lib/gl_array_oset.c
index 6a227b0..a6fdb06 100644 (file)
--- a/lib/gl_array_oset.c
+++ b/lib/gl_array_oset.c
@@ -105,6 +105,56 @@ gl_array_search (gl_oset_t set, const void *elt)
   return gl_array_indexof (set, elt) != (size_t)(-1);
 }
 
+static bool
+gl_array_search_atleast (gl_oset_t set,
+                        gl_setelement_threshold_fn threshold_fn,
+                        const void *threshold,
+                        const void **eltp)
+{
+  size_t count = set->count;
+
+  if (count > 0)
+    {
+      size_t low = 0;
+      size_t high = count;
+
+      /* At each loop iteration, low < high; for indices < low the values are
+        smaller than THRESHOLD; for indices >= high the values are nonexistent.
+        So, if an element >= THRESHOLD occurs in the list, it is at
+        low <= position < high.  */
+      do
+       {
+         size_t mid = low + (high - low) / 2; /* low <= mid < high */
+
+         if (! threshold_fn (set->elements[mid], threshold))
+           low = mid + 1;
+         else
+           {
+             /* We have an element >= THRESHOLD at index MID.  But we need the
+                minimal such index.  */
+             high = mid;
+             /* At each loop iteration, low <= high and
+                  compar (list->elements[high], value) >= 0,
+                and we know that the first occurrence of the element is at
+                low <= position <= high.  */
+             while (low < high)
+               {
+                 size_t mid2 = low + (high - low) / 2; /* low <= mid2 < high */
+
+                 if (! threshold_fn (set->elements[mid2], threshold))
+                   low = mid2 + 1;
+                 else
+                   high = mid2;
+               }
+             *eltp = set->elements[low];
+             return true;
+           }
+       }
+      while (low < high);
+    }
+  return false;
+}
+
 /* Ensure that set->allocated > set->count.  */
 static void
 grow (gl_oset_t set)
@@ -273,6 +323,7 @@ const struct gl_oset_implementation gl_array_oset_implementation =
     gl_array_create_empty,
     gl_array_size,
     gl_array_search,
+    gl_array_search_atleast,
     gl_array_add,
     gl_array_remove,
     gl_array_free,