kern/bitmap: new functions

Augment the interface with functions to search and iterate over zero bits.

1 files changed, 58 insertions, 0 deletions

diff --git a/kern/bitmap.c b/kern/bitmap.c
new file mode 100644
index 00000000..f1388b1d
--- /dev/null
+++ b/kern/bitmap.c
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2013 Richard Braun.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <kern/bitmap.h>
+#include <kern/limits.h>
+
+int
+bitmap_find_next_bit(volatile unsigned long *bm, int nr_bits, int bit,
+                     int complement)
+{
+    volatile unsigned long *start, *end;
+    unsigned long word;
+
+    start = bm;
+    end = bm + BITMAP_LONGS(nr_bits);
+
+    if (bit >= LONG_BIT)
+        bitmap_lookup(&bm, &bit);
+
+    word = *bm;
+
+    if (complement)
+        word = ~word;
+
+    if (bit < LONG_BIT)
+        word &= ~(bitmap_mask(bit) - 1);
+
+    for (;;) {
+        bit = __builtin_ffsl(word);
+
+        if (bit != 0)
+            return ((bm - start) * LONG_BIT) + bit - 1;
+
+        bm++;
+
+        if (bm >= end)
+            return -1;
+
+        word = *bm;
+
+        if (complement)
+            word = ~word;
+    }
+}