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| -rw-r--r-- | DOCS/tech/mpcf.txt | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/DOCS/tech/mpcf.txt b/DOCS/tech/mpcf.txt index 3fed86fd5e..7a0076bdbd 100644 --- a/DOCS/tech/mpcf.txt +++ b/DOCS/tech/mpcf.txt @@ -413,6 +413,24 @@ convert_ts Note: this calculation MUST be done with unsigned 64 bit integers, and is equivalent to (ln*sn)/(d1*d2) but this would require a 96bit integer +compare_ts + Compares timestamps from 2 different timebases, + if a is before b then compare_ts(a, b) = -1 + if a is after b then compare_ts(a, b) = 1 + else compare_ts(a, b) = 0 + + Care must be taken that this is done exactly with no rounding errors, + simply casting to float or double and doing the obvious + a*timebase > b*timebase is not compliant or correct, neither is the + same with integers, and + a*a_timebase.num*b_timebase.den > b*b_timebase.num*a_timebase.den + will overflow. One possible implementation which shouldn't overflow + within the range of legal timestamps and timebases is: + + if (convert_ts(a, a_timebase, b_timebase) < b) return -1; + if (convert_ts(b, b_timebase, a_timebase) < a) return 1; + return 0; + msb_pts_shift amount of bits in lsb_pts MUST be <16 |