4 #include <ccan/str/str.h>
8 #if HAVE_BUILTIN_EXPECT
10 * likely - indicate that a condition is likely to be true.
11 * @cond: the condition
13 * This uses a compiler extension where available to indicate a likely
14 * code path and optimize appropriately; it's also useful for readers
15 * to quickly identify exceptional paths through functions. The
16 * threshold for "likely" is usually considered to be between 90 and
17 * 99%; marginal cases should not be marked either way.
20 * unlikely(), likely_stats()
23 * // Returns false if we overflow.
24 * static inline bool inc_int(unsigned int *val)
32 #define likely(cond) __builtin_expect(!!(cond), 1)
35 * unlikely - indicate that a condition is unlikely to be true.
36 * @cond: the condition
38 * This uses a compiler extension where available to indicate an unlikely
39 * code path and optimize appropriately; see likely() above.
42 * likely(), likely_stats(), UNLIKELY_FUNCTION_ATTRIBUTE (compiler.h)
45 * // Prints a warning if we overflow.
46 * static inline void inc_int(unsigned int *val)
49 * if (unlikely(*val == 0))
50 * fprintf(stderr, "Overflow!");
53 #define unlikely(cond) __builtin_expect(!!(cond), 0)
55 #define likely(cond) (!!(cond))
56 #define unlikely(cond) (!!(cond))
58 #else /* DEBUG versions */
59 #define likely(cond) \
60 (_likely_trace(!!(cond), 1, stringify(cond), __FILE__, __LINE__))
61 #define unlikely(cond) \
62 (_likely_trace(!!(cond), 0, stringify(cond), __FILE__, __LINE__))
64 long _likely_trace(bool cond, bool expect,
66 const char *file, unsigned int line);
71 * likely_stats - return description of abused likely()/unlikely()
72 * @min_hits: minimum number of hits
73 * @percent: maximum percentage correct
75 * When DEBUG is defined, likely() and unlikely() trace their results: this
76 * causes a significant slowdown, but allows analysis of whether the stats
79 * This function returns a malloc'ed description of the least-correct
80 * usage of likely() or unlikely(). It ignores places which have been
81 * called less than @min_hits times, and those which were predicted
82 * correctly more than @percent of the time. It returns NULL when
83 * nothing meets those criteria.
85 * Note that this call is destructive; the returned offender is
86 * removed from the trace so that the next call to likely_stats() will
87 * return the next-worst likely()/unlikely() usage.
90 * // Print every place hit more than twice which was wrong > 5%.
91 * static void report_stats(void)
96 * while ((bad = likely_stats(2, 95)) != NULL) {
97 * printf("Suspicious likely: %s", bad);
103 const char *likely_stats(unsigned int min_hits, unsigned int percent);
105 #endif /* CCAN_LIKELY_H */