lib/bitmap.c: simplify bitmap_pos_to_ord

The ordinal of a set bit is simply the number of set bits before it;
counting those doesn't need to be done one bit at a time.  While at it,
update the parameters to unsigned int.

It is not completely unthinkable that gcc would see pos as compile-time
constant 0 in one of the uses of bitmap_pos_to_ord.  Since the static
inline frontend bitmap_weight doesn't handle nbits==0 correctly (it would
behave exactly as if nbits==BITS_PER_LONG), use __bitmap_weight.

Alternatively, the last line could be spelled bitmap_weight(buf, pos+1)-1,
but this is simpler.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/bitmap.c b/lib/bitmap.c
index b0d3e82..84d20b5 100644 (file)
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -744,10 +744,10 @@ EXPORT_SYMBOL(bitmap_parselist_user);
 /**
  * bitmap_pos_to_ord - find ordinal of set bit at given position in bitmap
  *     @buf: pointer to a bitmap
- *     @pos: a bit position in @buf (0 <= @pos < @bits)
- *     @bits: number of valid bit positions in @buf
+ *     @pos: a bit position in @buf (0 <= @pos < @nbits)
+ *     @nbits: number of valid bit positions in @buf
  *
- * Map the bit at position @pos in @buf (of length @bits) to the
+ * Map the bit at position @pos in @buf (of length @nbits) to the
  * ordinal of which set bit it is.  If it is not set or if @pos
  * is not a valid bit position, map to -1.
  *
@@ -759,22 +759,12 @@ EXPORT_SYMBOL(bitmap_parselist_user);
  *
  * The bit positions 0 through @bits are valid positions in @buf.
  */
-static int bitmap_pos_to_ord(const unsigned long *buf, int pos, int bits)
+static int bitmap_pos_to_ord(const unsigned long *buf, unsigned int pos, unsigned int nbits)
 {
-       int i, ord;
-
-       if (pos < 0 || pos >= bits || !test_bit(pos, buf))
+       if (pos >= nbits || !test_bit(pos, buf))
                return -1;
 
-       i = find_first_bit(buf, bits);
-       ord = 0;
-       while (i < pos) {
-               i = find_next_bit(buf, bits, i + 1);
-               ord++;
-       }
-       BUG_ON(i != pos);
-
-       return ord;
+       return __bitmap_weight(buf, pos);
 }
 
 /**