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Code Issues Releases Wiki Activity

util: New function raw_ctz().

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This will acquire a user in an upcoming commit.

Signed-off-by: Ben Pfaff <blp@nicira.com>
This commit is contained in:
Ben Pfaff
2012-08-21 10:47:22 -07:00
parent 3ca1de08b4
commit 0ee140fb69
2 changed files with 43 additions and 24 deletions
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42
lib/util.c
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@@ -790,38 +790,34 @@ log_2_ceil(uint32_t n)
return log_2_floor(n) + !IS_POW2(n);
}
/* Returns the number of trailing 0-bits in 'n', or 32 if 'n' is 0. */
int
ctz(uint32_t n)
{
if (!n) {
return 32;
} else {
/* Returns the number of trailing 0-bits in 'n'. Undefined if 'n' == 0. */
#if !defined(UINT_MAX) || !defined(UINT32_MAX)
#error "Someone screwed up the #includes."
#elif __GNUC__ >= 4 && UINT_MAX == UINT32_MAX
return __builtin_ctz(n);
/* Defined inline in util.h. */
#else
unsigned int k;
int count = 31;
static int
raw_ctz(uint32_t n)
{
unsigned int k;
int count = 31;
#define CTZ_STEP(X) \
k = n << (X); \
if (k) { \
count -= X; \
n = k; \
}
CTZ_STEP(16);
CTZ_STEP(8);
CTZ_STEP(4);
CTZ_STEP(2);
CTZ_STEP(1);
k = n << (X); \
if (k) { \
count -= X; \
n = k; \
}
CTZ_STEP(16);
CTZ_STEP(8);
CTZ_STEP(4);
CTZ_STEP(2);
CTZ_STEP(1);
#undef CTZ_STEP
return count;
#endif
}
return count;
}
#endif
/* Returns the number of 1-bits in 'x', between 0 and 32 inclusive. */
int

25
lib/util.h
View File

@@ -242,9 +242,32 @@ char *xreadlink(const char *filename);
char *follow_symlinks(const char *filename);
void ignore(bool x OVS_UNUSED);
/* Returns the number of trailing 0-bits in 'n'. Undefined if 'n' == 0.
*
* This compiles to a single machine instruction ("bsf") with GCC on x86. */
#if !defined(UINT_MAX) || !defined(UINT32_MAX)
#error "Someone screwed up the #includes."
#elif __GNUC__ >= 4 && UINT_MAX == UINT32_MAX
static inline int
raw_ctz(uint32_t n)
{
return __builtin_ctz(n);
}
#else
/* Defined in util.c. */
int raw_ctz(uint32_t n);
#endif
/* Returns the number of trailing 0-bits in 'n', or 32 if 'n' is 0. */
static inline int
ctz(uint32_t n)
{
return n ? raw_ctz(n) : 32;
}
int log_2_floor(uint32_t);
int log_2_ceil(uint32_t);
int ctz(uint32_t);
int popcount(uint32_t);
bool is_all_zeros(const uint8_t *, size_t);