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/*
* linux/fs/hfs/bitops.c
*
* Copyright (C) 1996 Paul H. Hargrove
* This file may be distributed under the terms of the GNU Public License.
*
* This file contains functions to handle bitmaps in "left-to-right"
* bit-order such that the MSB of a 32-bit big-endian word is bit 0.
* (This corresponds to bit 7 of a 32-bit little-endian word.)
*
* I have tested and confirmed that the results are identical on the
* Intel x86, PowerPC and DEC Alpha processors.
*
* "XXX" in a comment is a note to myself to consider changing something.
*/
#include "hfs.h"
/*================ Global functions ================*/
/*
* hfs_find_zero_bit()
*
* Description:
* Given a block of memory, its length in bits, and a starting bit number,
* determine the number of the first zero bits (in left-to-right ordering)
* in that range.
*
* Returns >= 'size' if no zero bits are found in the range.
*
* Accesses memory in 32-bit aligned chunks of 32-bits and thus
* may read beyond the 'size'th bit.
*/
hfs_u32 hfs_find_zero_bit(const hfs_u32 *start, hfs_u32 size, hfs_u32 offset)
{
const hfs_u32 *end = start + ((size + 31) >> 5);
const hfs_u32 *curr = start + (offset >> 5);
int bit = offset % 32;
if (offset < size) {
/* scan the first partial hfs_u32 for zero bits */
if (bit != 0) {
do {
if (!hfs_test_bit(bit, curr)) {
goto done;
}
++bit;
} while (bit < 32);
bit = 0;
++curr;
}
/* scan complete hfs_u32s for the first zero bit */
while (curr < end) {
if (*curr == ~((hfs_u32)0)) {
++curr;
} else {
while (hfs_test_bit(bit, curr)) {
++bit;
}
break;
}
}
done:
bit |= (curr - start) << 5;
return bit;
} else {
return size;
}
}
/*
* hfs_count_zero_bits()
*
* Description:
* Given a block of memory, its length in bits, and a starting bit number,
* determine the number of consecutive zero bits (in left-to-right ordering)
* in that range.
*
* Accesses memory in 32-bit aligned chunks of 32-bits and thus
* may read beyond the 'size'th bit.
*/
hfs_u32 hfs_count_zero_bits(const hfs_u32 *start, hfs_u32 size, hfs_u32 offset)
{
const hfs_u32 *end = start + ((size + 31) >> 5);
const hfs_u32 *curr = start + (offset >> 5);
int bit = offset % 32;
if (offset < size) {
/* scan the first partial hfs_u32 for one bits */
if (bit != 0) {
do {
if (hfs_test_bit(bit, curr)) {
goto done;
}
++bit;
} while (bit < 32);
bit = 0;
++curr;
}
/* scan complete hfs_u32s for the first one bit */
while (curr < end) {
if (*curr == ((hfs_u32)0)) {
++curr;
} else {
while (!hfs_test_bit(bit, curr)) {
++bit;
}
break;
}
}
done:
bit |= (curr - start) << 5;
if (bit > size) {
bit = size;
}
return bit - offset;
} else {
return 0;
}
}
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