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removed branchless code

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This commit is contained in:
Logan007 2020-07-23 02:17:08 +05:45
parent 36eb807fca
commit d3e823af98
1 changed files with 5 additions and 9 deletions
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14
src/n2n.c
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@ -428,12 +428,10 @@ uint64_t time_stamp (void) {
// checks if a provided time stamp is consistent with current time and previously valid time stamps
// returns the time stamp to store as "last valid time stamp" or zero in case of invalid time stamp
// uses branchless sign extensio tricks inspired by https://www.chessprogramming.org/Avoiding_Branches
// and also https://hbfs.wordpress.com/2008/08/05/branchless-equivalents-of-simple-functions
// REVISIT during the years 2035...2038
uint64_t time_stamp_verify (uint64_t stamp, uint64_t previous_stamp) {
int64_t diff; // do not change this to unsigned for keeping the following code work
int64_t diff; // do not change to unsigned
// is it higher than previous time stamp (including allowed deviation of TIME_STAMP_JITTER)?
diff = stamp - previous_stamp + TIME_STAMP_JITTER;
@ -441,16 +439,14 @@ uint64_t time_stamp_verify (uint64_t stamp, uint64_t previous_stamp) {
// is it around current time (+/- allowed deviation TIME_STAMP_FRAME)?
diff = stamp - time_stamp();
// branchless abs()
diff = (diff + (diff >> 63)) ^ (diff >> 63);
// abs()
diff = (diff < 0 ? -diff : diff);
if(diff < TIME_STAMP_FRAME) {
// for not allowing to exploit the allowed TIME_STAMP_JITTER to "turn the clock backwards",
// return the higher value making use of branchless max()
diff = stamp - previous_stamp;
diff = stamp - (diff & (diff >> 63));
return ((uint64_t)diff);
// return the higher value, max()
return (stamp > previous_stamp ? stamp : previous_stamp);
} else {
traceEvent(TRACE_DEBUG, "time_stamp_verify found a timestamp out of allowed frame.");