cutils: Add bitmask utilities to bitops

Bitmask utils handle resource tracking using a (multi-word) bitmask.

Change-Id: I2ae45df1ac8c665c29ea9cae32a757168686b96c

1 files changed, 68 insertions, 0 deletions

diff --git a/include/cutils/bitops.h b/include/cutils/bitops.h
index 1b3b762..6893985 100644
--- a/include/cutils/bitops.h
+++ b/include/cutils/bitops.h
@@ -17,10 +17,78 @@
 #ifndef __CUTILS_BITOPS_H
 #define __CUTILS_BITOPS_H
 
+#include <string.h>
+#include <strings.h>
 #include <sys/cdefs.h>
 
 __BEGIN_DECLS
 
+/*
+ * Bitmask Operations
+ *
+ * Note this doesn't provide any locking/exclusion, and isn't atomic.
+ * Additionally no bounds checking is done on the bitmask array.
+ *
+ * Example:
+ *
+ * int num_resources;
+ * unsigned int resource_bits[BITS_TO_WORDS(num_resources)];
+ * bitmask_init(resource_bits, num_resources);
+ * ...
+ * int bit = bitmask_ffz(resource_bits, num_resources);
+ * bitmask_set(resource_bits, bit);
+ * ...
+ * if (bitmask_test(resource_bits, bit)) { ... }
+ * ...
+ * bitmask_clear(resource_bits, bit);
+ *
+ */
+
+#define BITS_PER_WORD    (sizeof(unsigned int) * 8)
+#define BITS_TO_WORDS(x) (((x) + BITS_PER_WORD - 1) / BITS_PER_WORD)
+#define BIT_IN_WORD(x)   ((x) % BITS_PER_WORD)
+#define BIT_WORD(x)      ((x) / BITS_PER_WORD)
+#define BIT_MASK(x)      (1 << BIT_IN_WORD(x))
+
+static inline void bitmask_init(unsigned int *bitmask, int num_bits)
+{
+    memset(bitmask, 0, BITS_TO_WORDS(num_bits)*sizeof(unsigned int));
+}
+
+static inline int bitmask_ffz(unsigned int *bitmask, int num_bits)
+{
+    int bit, result;
+    unsigned int i;
+
+    for (i = 0; i < BITS_TO_WORDS(num_bits); i++) {
+        bit = ffs(~bitmask[i]);
+        if (bit) {
+            // ffs is 1-indexed, return 0-indexed result
+            bit--;
+            result = BITS_PER_WORD * i + bit;
+            if (result >= num_bits)
+                return -1;
+            return result;
+        }
+    }
+    return -1;
+}
+
+static inline void bitmask_set(unsigned int *bitmask, int bit)
+{
+    bitmask[BIT_WORD(bit)] |= BIT_MASK(bit);
+}
+
+static inline void bitmask_clear(unsigned int *bitmask, int bit)
+{
+    bitmask[BIT_WORD(bit)] &= ~BIT_MASK(bit);
+}
+
+static inline bool bitmask_test(unsigned int *bitmask, int bit)
+{
+    return bitmask[BIT_WORD(bit)] & BIT_MASK(bit);
+}
+
 static inline int popcount(unsigned int x)
 {
     return __builtin_popcount(x);