This function efficiently counts the number of bits in a block of
memory.
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
---
lib/ext2fs/bitops.c | 35 +++++++++++++++++++++++++++++++++++
lib/ext2fs/bitops.h | 1 +
lib/ext2fs/tst_bitmaps.c | 1 +
lib/ext2fs/tst_bitmaps_exp | 3 +++
4 files changed, 40 insertions(+)
diff --git a/lib/ext2fs/bitops.c b/lib/ext2fs/bitops.c
index 9322a35..7f5b66f 100644
--- a/lib/ext2fs/bitops.c
+++ b/lib/ext2fs/bitops.c
@@ -116,3 +116,38 @@ int ext2fs_test_bit64(__u64 nr, const void * addr)
return (mask & *ADDR);
}
+static unsigned int popcount8(unsigned int w)
+{
+ unsigned int res = w - ((w >> 1) & 0x55);
+ res = (res & 0x33) + ((res >> 2) & 0x33);
+ return (res + (res >> 4)) & 0x0F;
+}
+
+static unsigned int popcount32(unsigned int w)
+{
+ unsigned int res = w - ((w >> 1) & 0x55555555);
+ res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
+ res = (res + (res >> 4)) & 0x0F0F0F0F;
+ res = res + (res >> 8);
+ return (res + (res >> 16)) & 0x000000FF;
+}
+
+unsigned int ext2fs_bitcount(const void *addr, unsigned int count)
+{
+ const unsigned char *cp = addr;
+ const __u32 *p = addr;
+ unsigned int res = 0;
+
+ if ((((unsigned long) addr) & 3) == 0) {
+ while (count > 4) {
+ res += popcount32(*p++);
+ count -= 4;
+ }
+ cp = (const unsigned char *) p;
+ }
+ while (count > 0) {
+ res += popcount8(*cp++);
+ count--;
+ }
+ return res;
+}
diff --git a/lib/ext2fs/bitops.h b/lib/ext2fs/bitops.h
index 526870f..17e707c 100644
--- a/lib/ext2fs/bitops.h
+++ b/lib/ext2fs/bitops.h
@@ -686,6 +686,7 @@ extern int ext2fs_test_bit(unsigned int nr, const void * addr);
extern int ext2fs_set_bit64(__u64 nr,void * addr);
extern int ext2fs_clear_bit64(__u64 nr, void * addr);
extern int ext2fs_test_bit64(__u64 nr, const void * addr);
+extern unsigned int ext2fs_bitcount(const void *addr, unsigned int count);
#ifdef NO_INLINE_FUNCS
extern void ext2fs_fast_set_bit(unsigned int nr,void * addr);
diff --git a/lib/ext2fs/tst_bitmaps.c b/lib/ext2fs/tst_bitmaps.c
index 5da3693..2a76292 100644
--- a/lib/ext2fs/tst_bitmaps.c
+++ b/lib/ext2fs/tst_bitmaps.c
@@ -270,6 +270,7 @@ void dump_bitmap(ext2fs_generic_bitmap bmap, unsigned int start, unsigned num)
for (i=0; i < len; i++)
printf("%02x", buf[i]);
printf("\n");
+ printf("bits set: %u\n", ext2fs_bitcount(buf, len));
free(buf);
}
diff --git a/lib/ext2fs/tst_bitmaps_exp b/lib/ext2fs/tst_bitmaps_exp
index 2d406ce..893f315 100644
--- a/lib/ext2fs/tst_bitmaps_exp
+++ b/lib/ext2fs/tst_bitmaps_exp
@@ -36,6 +36,7 @@ tst_bitmaps: testb 16
Block 16 is set
tst_bitmaps: dump_bb
block bitmap: 00f80000000000000000000000000000
+bits set: 5
tst_bitmaps: ffzb 11 16
First unmarked block is 11
tst_bitmaps: ffzb 12 16
@@ -64,6 +65,7 @@ tst_bitmaps: setb 12 7
Marking blocks 12 to 18
tst_bitmaps: dump_bb
block bitmap: 00f80300000000000000000000000000
+bits set: 7
tst_bitmaps: seti 2
Setting inode 2, was clear before
tst_bitmaps: seti 5
@@ -82,6 +84,7 @@ tst_bitmaps: testi 1
Inode 1 is clear
tst_bitmaps: dump_ib
inode bitmap: 1e000000
+bits set: 4
tst_bitmaps: ffzi 1 6
First unmarked inode is 1
tst_bitmaps: ffzi 2 5
--
1.7.12.rc0.22.gcdd159b
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