1 files changed, 20 insertions, 0 deletions
diff --git a/source/blender/blenlib/intern/bitmap.c b/source/blender/blenlib/intern/bitmap.c
index 7fcbc31c066..2cc2fbc3e2f 100644
--- a/source/blender/blenlib/intern/bitmap.c
+++ b/source/blender/blenlib/intern/bitmap.c
@@ -11,6 +11,7 @@
 #include <string.h>
 
 #include "BLI_bitmap.h"
+#include "BLI_math_bits.h"
 #include "BLI_utildefines.h"
 
 void BLI_bitmap_set_all(BLI_bitmap *bitmap, bool set, size_t bits)
@@ -46,3 +47,22 @@ void BLI_bitmap_or_all(BLI_bitmap *dst, const BLI_bitmap *src, size_t bits)
     dst[i] |= src[i];
   }
 }
+
+int BLI_bitmap_find_first_unset(const BLI_bitmap *bitmap, const size_t bits)
+{
+  const size_t blocks_num = _BITMAP_NUM_BLOCKS(bits);
+  int result = -1;
+  /* Skip over completely set blocks. */
+  int index = 0;
+  while (index < blocks_num && bitmap[index] == ~0u) {
+    index++;
+  }
+  if (index < blocks_num) {
+    /* Found a partially used block: find the lowest unused bit. */
+    const uint m = ~bitmap[index];
+    BLI_assert(m != 0);
+    const uint bit_index = bitscan_forward_uint(m);
+    result = bit_index + (index << _BITMAP_POWER);
+  }
+  return result;
+}