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(find_transition): Instead of a linear search try to guess the transition index, use a linear search if the result is at most 10 transitions away from the guess or binary search otherwise.

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This commit is contained in:
Ulrich Drepper 2007-03-05 19:32:03 +00:00
parent fe64626c13
commit 132526780a
1 changed files with 50 additions and 3 deletions
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53
time/tzfile.c
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@ -548,13 +548,60 @@ find_transition (time_t timer)
if (i == num_types)
i = 0;
}
else if (timer >= transitions[num_transitions - 1])
i = type_idxs[num_transitions - 1];
else
{
/* Find the first transition after TIMER, and
then pick the type of the transition before it. */
for (i = 1; i < num_transitions; ++i)
if (timer < transitions[i])
break;
size_t lo = 0;
size_t hi = num_transitions - 1;
/* Assume that DST is changing twice a year and guess initial
search spot from it.
Half of a gregorian year has on average 365.2425 * 86400 / 2
= 15778476 seconds. */
i = (transitions[num_transitions - 1] - timer) / 15778476;
if (i < num_transitions)
{
i = num_transitions - 1 - i;
if (timer < transitions[i])
{
if (i < 10 || timer >= transitions[i - 10])
{
/* Linear search. */
while (timer < transitions[i - 1])
--i;
goto found;
}
hi = i - 10;
}
else
{
if (i + 10 >= num_transitions || timer < transitions[i + 10])
{
/* Linear search. */
while (timer >= transitions[i])
++i;
goto found;
}
lo = i + 10;
}
}
/* Binary search. */
/* assert (timer >= transitions[lo] && timer < transitions[hi]); */
while (lo + 1 < hi)
{
i = (lo + hi) / 2;
if (timer < transitions[i])
hi = i;
else
lo = i;
}
i = hi;
found:
/* assert (timer >= transitions[i - 1] && timer < transitions[i]); */
i = type_idxs[i - 1];
}