/*
- * bitops.h
+ * bitops.h - inline functions for bit manipulation
*
- * Inline functions for bit manipulation.
+ * The following copying information applies to this specific source code file:
*
- * The author dedicates this file to the public domain.
- * You can do whatever you want with this file.
+ * Written in 2014-2016 by Eric Biggers <ebiggers3@gmail.com>
+ *
+ * To the extent possible under law, the author(s) have dedicated all copyright
+ * and related and neighboring rights to this software to the public domain
+ * worldwide via the Creative Commons Zero 1.0 Universal Public Domain
+ * Dedication (the "CC0").
+ *
+ * This software is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the CC0 for more details.
+ *
+ * You should have received a copy of the CC0 along with this software; if not
+ * see <http://creativecommons.org/publicdomain/zero/1.0/>.
*/
#ifndef _WIMLIB_BITOPS_H
#include "wimlib/compiler.h"
#include "wimlib/types.h"
-/* Find Last Set bit */
+/*
+ * Bit Scan Reverse (BSR) - find the 0-based index (relative to the least
+ * significant bit) of the *most* significant 1 bit in the input value. The
+ * input value must be nonzero!
+ */
-static inline unsigned
-fls32(u32 v)
+static forceinline unsigned
+bsr32(u32 v)
{
-#ifdef compiler_fls32
- return compiler_fls32(v);
+#ifdef compiler_bsr32
+ return compiler_bsr32(v);
#else
unsigned bit = 0;
while ((v >>= 1) != 0)
#endif
}
-static inline unsigned
-fls64(u64 v)
+static forceinline unsigned
+bsr64(u64 v)
{
-#ifdef compiler_fls64
- return compiler_fls64(v);
+#ifdef compiler_bsr64
+ return compiler_bsr64(v);
#else
unsigned bit = 0;
while ((v >>= 1) != 0)
#endif
}
-static inline unsigned
-flsw(machine_word_t v)
+static forceinline unsigned
+bsrw(machine_word_t v)
{
- STATIC_ASSERT(WORDSIZE == 4 || WORDSIZE == 8);
- if (WORDSIZE == 4)
- return fls32(v);
+ STATIC_ASSERT(WORDBITS == 32 || WORDBITS == 64);
+ if (WORDBITS == 32)
+ return bsr32(v);
else
- return fls64(v);
+ return bsr64(v);
}
-/* Find First Set bit */
+/*
+ * Bit Scan Forward (BSF) - find the 0-based index (relative to the least
+ * significant bit) of the *least* significant 1 bit in the input value. The
+ * input value must be nonzero!
+ */
-static inline unsigned
-ffs32(u32 v)
+static forceinline unsigned
+bsf32(u32 v)
{
-#ifdef compiler_ffs32
- return compiler_ffs32(v);
+#ifdef compiler_bsf32
+ return compiler_bsf32(v);
#else
unsigned bit;
for (bit = 0; !(v & 1); bit++, v >>= 1)
#endif
}
-static inline unsigned
-ffs64(u64 v)
+static forceinline unsigned
+bsf64(u64 v)
{
-#ifdef compiler_ffs64
- return compiler_ffs64(v);
+#ifdef compiler_bsf64
+ return compiler_bsf64(v);
#else
unsigned bit;
for (bit = 0; !(v & 1); bit++, v >>= 1)
#endif
}
-static inline unsigned
-ffsw(machine_word_t v)
+static forceinline unsigned
+bsfw(machine_word_t v)
{
- STATIC_ASSERT(WORDSIZE == 4 || WORDSIZE == 8);
- if (WORDSIZE == 4)
- return ffs32(v);
+ STATIC_ASSERT(WORDBITS == 32 || WORDBITS == 64);
+ if (WORDBITS == 32)
+ return bsf32(v);
else
- return ffs64(v);
+ return bsf64(v);
}
-/* Round up to nearest power of 2 */
+/* Return the log base 2 of 'n', rounded up to the nearest integer. */
+static forceinline unsigned
+ilog2_ceil(size_t n)
+{
+ if (n <= 1)
+ return 0;
+ return 1 + bsrw(n - 1);
+}
-static inline size_t
+/* Round 'n' up to the nearest power of 2 */
+static forceinline size_t
roundup_pow_of_2(size_t n)
{
- if (n <= 1)
- return 1;
- return (size_t)1 << (1 + flsw(n - 1));
+ return (size_t)1 << ilog2_ceil(n);
}
#endif /* _WIMLIB_BITOPS_H */