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[MINOR] time: add __usec_to_1024th to convert usecs to 1024th of second

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This function performs a fast conversion from usec to 1024th of a second,
and will be useful for many fast sub-second computations.
This commit is contained in:
Willy Tarreau 2009-03-05 00:34:01 +01:00
parent defc52da95
commit 776cd87e32
1 changed files with 12 additions and 0 deletions
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12
include/common/time.h
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@ -157,6 +157,18 @@ REGPRM2 static inline struct timeval * __tv_from_ms(struct timeval *tv, unsigned
return tv;
}
/* Return a number of 1024Hz ticks between 0 and 1023 for input number of
* usecs between 0 and 999999. This function has been optimized to remove
* any divide and multiply, as it is completely optimized away by the compiler
* on CPUs which don't have a fast multiply. Its avg error rate is 305 ppm,
* which is almost twice as low as a direct usec to ms conversion. This version
* also has the benefit of returning 1024 for 1000000.
*/
REGPRM1 static inline unsigned int __usec_to_1024th(unsigned int usec)
{
return (usec * 1073 + 742516) >> 20;
}
/**** comparison functions and macros ***********************************/