cogl-bitmask: Add _cogl_bitmask_popcount

This returns a population count of all the bits that are set in the
bitmask.

There is now also a _cogl_bitmask_popcount_upto which counts the
number of bits set up to but not including the given bit index. This
will be useful to determine the number of uniform overrides to skip if
we tightly pack the values in an array.

The test-bitmask test has been modified to check these two functions.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

cogl/cogl-bitmask.c

@@ -271,3 +271,41 @@ _cogl_bitmask_set_flags_array (const CoglBitmask *bitmask,
   for (i = 0; i < array->len; i++)
     flags[i] |= g_array_index (array, unsigned long, i);
 }
+
+int
+_cogl_bitmask_popcount_in_array (const CoglBitmask *bitmask)
+{
+  const GArray *array = (const GArray *) *bitmask;
+  int pop = 0;
+  int i;
+
+  for (i = 0; i < array->len; i++)
+    pop += _cogl_util_popcountl (g_array_index (array, unsigned long, i));
+
+  return pop;
+}
+
+int
+_cogl_bitmask_popcount_upto_in_array (const CoglBitmask *bitmask,
+                                      int upto)
+{
+  const GArray *array = (const GArray *) *bitmask;
+
+  if (upto >= array->len * sizeof (unsigned long) * 8)
+    return _cogl_bitmask_popcount_in_array (bitmask);
+  else
+    {
+      unsigned long top_mask;
+      int array_index = ARRAY_INDEX (upto);
+      int bit_index = BIT_INDEX (upto);
+      int pop = 0;
+      int i;
+
+      for (i = 0; i < array_index; i++)
+        pop += _cogl_util_popcountl (g_array_index (array, unsigned long, i));
+
+      top_mask = g_array_index (array, unsigned long, array_index);
+
+      return pop + _cogl_util_popcountl (top_mask & ((1UL << bit_index) - 1));
+    }
+}

cogl/cogl-bitmask.h

@@ -28,6 +28,7 @@
 #define __COGL_BITMASK_H
 
 #include <glib.h>
+#include "cogl-util.h"
 
 G_BEGIN_DECLS
 
@@ -104,6 +105,14 @@ _cogl_bitmask_clear_all_in_array (CoglBitmask *bitmask);
 void
 _cogl_bitmask_set_flags_array (const CoglBitmask *bitmask,
                                unsigned long *flags);
+
+int
+_cogl_bitmask_popcount_in_array (const CoglBitmask *bitmask);
+
+int
+_cogl_bitmask_popcount_upto_in_array (const CoglBitmask *bitmask,
+                                      int upto);
+
 /*
  * cogl_bitmask_set_bits:
  * @dst: The bitmask to modify
@@ -254,6 +263,45 @@ _cogl_bitmask_set_flags (const CoglBitmask *bitmask,
     flags[0] |= _cogl_bitmask_to_bits (bitmask);
 }
 
+/*
+ * _cogl_bitmask_popcount:
+ * @bitmask: A pointer to a bitmask
+ *
+ * Counts the number of bits that are set in the bitmask.
+ *
+ * Return value: the number of bits set in @bitmask.
+ */
+static inline int
+_cogl_bitmask_popcount (const CoglBitmask *bitmask)
+{
+  return (_cogl_bitmask_has_array (bitmask) ?
+          _cogl_bitmask_popcount_in_array (bitmask) :
+          _cogl_util_popcountl (_cogl_bitmask_to_bits (bitmask)));
+}
+
+/*
+ * _cogl_bitmask_popcount:
+ * @Bitmask: A pointer to a bitmask
+ * @upto: The maximum bit index to consider
+ *
+ * Counts the number of bits that are set and have an index which is
+ * less than @upto.
+ *
+ * Return value: the number of bits set in @bitmask that are less than @upto.
+ */
+static inline int
+_cogl_bitmask_popcount_upto (const CoglBitmask *bitmask,
+                             int upto)
+{
+  if (_cogl_bitmask_has_array (bitmask))
+    return _cogl_bitmask_popcount_upto_in_array (bitmask, upto);
+  else if (upto >= COGL_BITMASK_MAX_DIRECT_BITS)
+    return _cogl_util_popcountl (_cogl_bitmask_to_bits (bitmask));
+  else
+    return _cogl_util_popcountl (_cogl_bitmask_to_bits (bitmask) &
+                                 ((1UL << upto) - 1));
+}
+
 G_END_DECLS
 
 #endif /* __COGL_BITMASK_H */

tests/conform/test-bitmask.c

@@ -62,12 +62,25 @@ verify_bits (const CoglBitmask *bitmask,
   for (i = 0; i < data.n_bits; i++)
     g_assert_cmpint (data.bits[i], ==, -1);
 
+  g_assert_cmpint (_cogl_bitmask_popcount (bitmask), ==, data.n_bits);
+
   for (i = 0; i < 1024; i++)
     {
+      int upto_popcount = 0;
       int j;
 
       G_VA_COPY (ap, ap_copy);
 
+      for (j = 0; j < data.n_bits; j++)
+        if (va_arg (ap, int) < i)
+          upto_popcount++;
+
+      g_assert_cmpint (_cogl_bitmask_popcount_upto (bitmask, i),
+                       ==,
+                       upto_popcount);
+
+      G_VA_COPY (ap, ap_copy);
+
       for (j = 0; j < data.n_bits; j++)
         if (va_arg (ap, int) == i)
           break;