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 <sumit6307@gmail.com>

fs/mnemofs/mnemofs.h

@@ -345,14 +345,14 @@ static inline mfs_t mfs_ctz(const uint32_t x)
 
       return 0;
     }
-
 #if defined(__GNUC__)
   return __builtin_ctz(x);
 #else
   uint32_t c;
 
   /* Credits:
- * http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightBinSearch
+   * http://graphics.stanford.edu/~seander/bithacks.html
+   * #ZerosOnRightBinSearch
    */
 
   if (x & 0x1)
@@ -369,27 +369,47 @@ static inline mfs_t mfs_ctz(const uint32_t x)
           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;
     }
+
   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))
@@ -400,11 +420,47 @@ static inline mfs_t mfs_clz(const uint32_t x)
 
       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);
 
 /****************************************************************************

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);