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new bd5e017ebd7 fs/mnemofs: Add portable bit primitives and cleanup hash
functions
bd5e017ebd7 is described below
commit bd5e017ebd78783a7d8dc4b8afec4dce9cdc3fae
Author: Sumit6307 <[email protected]>
AuthorDate: Tue Mar 10 01:30:59 2026 +0530
fs/mnemofs: Add portable bit primitives and cleanup hash functions
This PR addresses several portability and technical debt issues in the
mnemofs filesystem by resolving source-level TODO items.
Changes:
- Implemented a portable fallback for mfs\_clz (Count Leading Zeros) in
fs/mnemofs/mnemofs.h using a binary search approach. This ensures compatibility
with non-GCC compilers.
- Removed the redundant 8-bit mfs\_arrhash and consolidated hashing with
the existing 16-bit mfs\_hash in mnemofs\_util.c.
- Removed the related TODO comments in mnemofs.h and mnemofs\_util.c.
- Fixed NuttX style (indentation and braces) in the fallback bit primitives.
Signed-off-by: Sumit <[email protected]>
---
fs/mnemofs/mnemofs.h | 148 +++++++++++++++++++++++++++++++---------------
fs/mnemofs/mnemofs_util.c | 23 -------
2 files changed, 100 insertions(+), 71 deletions(-)
diff --git a/fs/mnemofs/mnemofs.h b/fs/mnemofs/mnemofs.h
index fa346eabc28..5a0a47c2152 100644
--- a/fs/mnemofs/mnemofs.h
+++ b/fs/mnemofs/mnemofs.h
@@ -338,73 +338,129 @@ static mfs_t inline mfs_blkremsz(FAR const struct
mfs_sb_s * const sb,
static inline mfs_t mfs_ctz(const uint32_t x)
{
if (predict_false(x == 0))
- {
-/* Special case, since we're using this for the CTZ skip list. The 0th
- * block has no pointers.
- */
-
- return 0;
- }
+ {
+ /* Special case, since we're using this for the CTZ skip list. The 0th
+ * block has no pointers.
+ */
+ return 0;
+ }
#if defined(__GNUC__)
return __builtin_ctz(x);
#else
uint32_t c;
-/* Credits:
- * http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightBinSearch
- */
+ /* Credits:
+ * http://graphics.stanford.edu/~seander/bithacks.html
+ * #ZerosOnRightBinSearch
+ */
if (x & 0x1)
- {
- /* special case for odd x (assumed to happen half of the time) */
-
- c = 0;
- }
- else
- {
- c = 1;
- if ((x & 0xffff) == 0)
- {
- x >>= 16;
- c += 16;
- }
- if ((x & 0xff) == 0)
{
- x >>= 8;
- c += 8;
- }
- if ((x & 0xf) == 0)
- {
- x >>= 4;
- c += 4;
+ /* special case for odd x (assumed to happen half of the time) */
+
+ c = 0;
}
- if ((x & 0x3) == 0)
+ else
{
- x >>= 2;
- c += 2;
+ c = 1;
+ if ((x & 0xffff) == 0)
+ {
+ x >>= 16;
+ c += 16;
+ }
+
+ if ((x & 0xff) == 0)
+ {
+ x >>= 8;
+ c += 8;
+ }
+
+ if ((x & 0xf) == 0)
+ {
+ x >>= 4;
+ c += 4;
+ }
+
+ if ((x & 0x3) == 0)
+ {
+ x >>= 2;
+ c += 2;
+ }
+
+ c -= x & 0x1;
}
- c -= x & 0x1;
- }
+
return c;
#endif
}
+/****************************************************************************
+ * Name: mfs_clz
+ *
+ * Description:
+ * Count Leading Zeros. Returns the number of leading zeros in a 32-bit
+ * integer.
+ *
+ * Input Parameters:
+ * x - 32-bit integer to check.
+ *
+ * Returned Value:
+ * The number of leading zeros.
+ *
+ ****************************************************************************/
+
static inline mfs_t mfs_clz(const uint32_t x)
{
if (predict_false(x == UINT32_MAX))
- {
-/* Special case, since we're using this for the CTZ skip list. The 0th
- * block has no pointers.
- */
-
- return 0;
- }
+ {
+ /* Special case, since we're using this for the CTZ skip list. The 0th
+ * block has no pointers.
+ */
+ return 0;
+ }
#if defined(__GNUC__)
return __builtin_clz(x);
#else
- return 0; /* TODO */
+ uint32_t n = 0;
+ uint32_t x_tmp = x;
+
+ if (x_tmp == 0)
+ {
+ return 32;
+ }
+
+ if (x_tmp <= 0x0000ffff)
+ {
+ n += 16;
+ x_tmp <<= 16;
+ }
+
+ if (x_tmp <= 0x00ffffff)
+ {
+ n += 8;
+ x_tmp <<= 8;
+ }
+
+ if (x_tmp <= 0x0fffffff)
+ {
+ n += 4;
+ x_tmp <<= 4;
+ }
+
+ if (x_tmp <= 0x3fffffff)
+ {
+ n += 2;
+ x_tmp <<= 2;
+ }
+
+ if (x_tmp <= 0x7fffffff)
+ {
+ n += 1;
+ }
+
+ return n;
#endif
}
@@ -1041,10 +1097,6 @@ int mfs_erase_nblks(FAR const struct mfs_sb_s * const
sb, const off_t blk,
*
****************************************************************************/
-uint8_t mfs_arrhash(FAR const char *arr, ssize_t len);
-
-/* TODO: Put below in place of above. */
-
uint16_t mfs_hash(FAR const char *arr, ssize_t len);
/****************************************************************************
diff --git a/fs/mnemofs/mnemofs_util.c b/fs/mnemofs/mnemofs_util.c
index b6edb9cf197..b98661ee88e 100644
--- a/fs/mnemofs/mnemofs_util.c
+++ b/fs/mnemofs/mnemofs_util.c
@@ -87,35 +87,12 @@
* Public Functions
****************************************************************************/
-uint8_t mfs_arrhash(FAR const char *arr, ssize_t len)
-{
- ssize_t l = 0;
- ssize_t r = len - 1;
- uint16_t hash = 0;
-
- /* TODO: Change the array checksum to be 16 bit long. */
-
- while (l <= r)
- {
- hash += arr[l] * arr[r] * (l + 1) * (r + 1);
- l++;
- r--;
- hash %= (1 << 8);
- }
-
- finfo("Hash calculated for size %zd to be %d.", len, hash % (1 << 8));
-
- return hash % (1 << 8);
-}
-
uint16_t mfs_hash(FAR const char *arr, ssize_t len)
{
ssize_t l = 0;
ssize_t r = len - 1;
uint32_t hash = 0;
- /* TODO: Change the array checksum to be 16 bit long. */
-
while (l <= r)
{
hash += arr[l] * arr[r] * (l + 1) * (r + 1);
