libext2fs: add ext2fs_bitcount() function

This function efficiently counts the number of bits in a block of
memory.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>

lib/ext2fs/bitops.c

@@ -116,3 +116,43 @@ 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 nbytes)
+{
+	const unsigned char *cp = addr;
+	const __u32 *p;
+	unsigned int res = 0;
+
+	while (((((unsigned long) cp) & 3) != 0) && (nbytes > 0)) {
+		res += popcount8(*cp++);
+		nbytes--;
+	}
+	p = (__u32 *) cp;
+
+	while (nbytes > 4) {
+		res += popcount32(*p++);
+		nbytes -= 4;
+	}
+	cp = (const unsigned char *) p;
+
+	while (nbytes > 0) {
+		res += popcount8(*cp++);
+		nbytes--;
+	}
+	return res;
+}

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 nbytes);
 
 #ifdef NO_INLINE_FUNCS
 extern void ext2fs_fast_set_bit(unsigned int nr,void * addr);

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);
 }
 

lib/ext2fs/tst_bitmaps_cmds

@@ -53,5 +53,47 @@ cleari 5
 testi 17
 testi 6
 testi 4
+clearb 7 12
+dump_bb
+setb 1
+dump_bb
+setb 2
+dump_bb
+setb 3
+dump_bb
+setb 4
+dump_bb
+setb 5
+dump_bb
+setb 6
+dump_bb
+setb 7
+dump_bb
+setb 8
+dump_bb
+setb 10
+setb 12
+setb 14
+setb 17
+setb 19
+setb 24
+setb 26
+setb 27
+setb 30
+setb 31
+setb 32
+setb 35
+setb 39
+setb 40
+setb 44
+setb 46
+setb 47
+setb 49
+setb 51
+setb 52
+clearb 2
+clearb 3
+clearb 7
+dump_bb
 quit
 

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
@@ -110,5 +113,99 @@ tst_bitmaps: testi 6
 Inode 6 is clear
 tst_bitmaps: testi 4
 Inode 4 is clear
+tst_bitmaps: clearb 7 12
+Clearing blocks 7 to 18
+tst_bitmaps: dump_bb
+block bitmap: 00000000000000000000000000000000
+bits set: 0
+tst_bitmaps: setb 1
+Setting block 1, was clear before
+tst_bitmaps: dump_bb
+block bitmap: 01000000000000000000000000000000
+bits set: 1
+tst_bitmaps: setb 2
+Setting block 2, was clear before
+tst_bitmaps: dump_bb
+block bitmap: 03000000000000000000000000000000
+bits set: 2
+tst_bitmaps: setb 3
+Setting block 3, was clear before
+tst_bitmaps: dump_bb
+block bitmap: 07000000000000000000000000000000
+bits set: 3
+tst_bitmaps: setb 4
+Setting block 4, was clear before
+tst_bitmaps: dump_bb
+block bitmap: 0f000000000000000000000000000000
+bits set: 4
+tst_bitmaps: setb 5
+Setting block 5, was clear before
+tst_bitmaps: dump_bb
+block bitmap: 1f000000000000000000000000000000
+bits set: 5
+tst_bitmaps: setb 6
+Setting block 6, was clear before
+tst_bitmaps: dump_bb
+block bitmap: 3f000000000000000000000000000000
+bits set: 6
+tst_bitmaps: setb 7
+Setting block 7, was clear before
+tst_bitmaps: dump_bb
+block bitmap: 7f000000000000000000000000000000
+bits set: 7
+tst_bitmaps: setb 8
+Setting block 8, was clear before
+tst_bitmaps: dump_bb
+block bitmap: ff000000000000000000000000000000
+bits set: 8
+tst_bitmaps: setb 10
+Setting block 10, was clear before
+tst_bitmaps: setb 12
+Setting block 12, was clear before
+tst_bitmaps: setb 14
+Setting block 14, was clear before
+tst_bitmaps: setb 17
+Setting block 17, was clear before
+tst_bitmaps: setb 19
+Setting block 19, was clear before
+tst_bitmaps: setb 24
+Setting block 24, was clear before
+tst_bitmaps: setb 26
+Setting block 26, was clear before
+tst_bitmaps: setb 27
+Setting block 27, was clear before
+tst_bitmaps: setb 30
+Setting block 30, was clear before
+tst_bitmaps: setb 31
+Setting block 31, was clear before
+tst_bitmaps: setb 32
+Setting block 32, was clear before
+tst_bitmaps: setb 35
+Setting block 35, was clear before
+tst_bitmaps: setb 39
+Setting block 39, was clear before
+tst_bitmaps: setb 40
+Setting block 40, was clear before
+tst_bitmaps: setb 44
+Setting block 44, was clear before
+tst_bitmaps: setb 46
+Setting block 46, was clear before
+tst_bitmaps: setb 47
+Setting block 47, was clear before
+tst_bitmaps: setb 49
+Setting block 49, was clear before
+tst_bitmaps: setb 51
+Setting block 51, was clear before
+tst_bitmaps: setb 52
+Setting block 52, was clear before
+tst_bitmaps: clearb 2
+Clearing block 2, was set before
+tst_bitmaps: clearb 3
+Clearing block 3, was set before
+tst_bitmaps: clearb 7
+Clearing block 7, was set before
+tst_bitmaps: dump_bb
+block bitmap: b92a85e6c4680d000000000000000000
+bits set: 25
 tst_bitmaps: quit
 tst_bitmaps: