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Fix edge-case behavior of pg_next_dst_boundary().

Due to rather sloppy thinking (on my part, I'm afraid) about theappropriate behavior for boundary conditions, pg_next_dst_boundary() gaveundefined, platform-dependent results when the input time is exactly thelast recorded DST transition time for the specified time zone, as a resultof fetching values one past the end of its data arrays.Change its specification to be that it always finds the next DST boundary*after* the input time, and adjust code to match that. The sole existingcaller, DetermineTimeZoneOffset, doesn't actually care about thisdistinction, since it always uses a probe time earlier than the instantthat it does care about. So it seemed best to me to change the API to makethe result=1 and result=0 cases more consistent, specifically to ensurethat the "before" outputs always describe the state at the given time,rather than hacking the code to obey the previous API comment exactly.Per bug #6605 from Sergey Burladyan. Back-patch to all supported versions.

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src/timezone
- localtime.c

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`‎src/timezone/localtime.c`

Lines changed: 12 additions & 11 deletions

Original file line number	Diff line number	Diff line change
`@@ -1292,20 +1292,21 @@ increment_overflow(int *number, int delta)`
`1292`	`1292`	`}`
`1293`	`1293`
`1294`	`1294`	`/*`
`1295`		`- * Find the next DST transition timeat orafter the given time`
	`1295`	`+ * Find the next DST transition time after the given time`
`1296`	`1296`	`*`
`1297`	`1297`	`* *timep is the input value, the other parameters are output values.`
`1298`	`1298`	`*`
`1299`	`1299`	`* When the function result is 1, *boundary is set to the time_t`
`1300`		`- * representation of the next DST transition timeat orafter *timep,`
	`1300`	`+ * representation of the next DST transition time after *timep,`
`1301`	`1301`	`* before_gmtoff and before_isdst are set to the GMT offset and isdst`
`1302`		`- * state prevailing just before that boundary, and *after_gmtoff and`
`1303`		`- * *after_isdst are set to the state prevailing just after that boundary.`
	`1302`	`+ * state prevailing just before that boundary (in particular, the state`
	`1303`	`+ * prevailing at timep), and after_gmtoff and *after_isdst are set to`
	`1304`	`+ * the state prevailing just after that boundary.`
`1304`	`1305`	`*`
`1305`		`- * When the function result is 0, there is no known DST transition at or`
	`1306`	`+ * When the function result is 0, there is no known DST transition`
`1306`	`1307`	`* after timep, but before_gmtoff and *before_isdst indicate the GMT`
`1307`	`1308`	`* offset and isdst state prevailing at *timep. (This would occur in`
`1308`		`- * DST-less time zones,for example.)`
	`1309`	`+ * DST-less time zones,or if a zone has permanently ceased using DST.)`
`1309`	`1310`	`*`
`1310`	`1311`	`* A function result of -1 indicates failure (this case does not actually`
`1311`	`1312`	`* occur in our current implementation).`
`@@ -1385,16 +1386,16 @@ pg_next_dst_boundary(const pg_time_t *timep,`
`1385`	`1386`	`returnresult;`
`1386`	`1387`	`}`
`1387`	`1388`
`1388`		`-if (t>sp->ats[sp->timecnt-1])`
	`1389`	`+if (t >=sp->ats[sp->timecnt-1])`
`1389`	`1390`	`{`
`1390`		`-/* No known transition >= t, so use last known segment's type */`
	`1391`	`+/* No known transition > t, so use last known segment's type */`
`1391`	`1392`	`i=sp->types[sp->timecnt-1];`
`1392`	`1393`	`ttisp=&sp->ttis[i];`
`1393`	`1394`	`*before_gmtoff=ttisp->tt_gmtoff;`
`1394`	`1395`	`*before_isdst=ttisp->tt_isdst;`
`1395`	`1396`	`return0;`
`1396`	`1397`	`}`
`1397`		`-if (t <=sp->ats[0])`
	`1398`	`+if (t<sp->ats[0])`
`1398`	`1399`	`{`
`1399`	`1400`	`/* For "before", use lowest-numbered standard type */`
`1400`	`1401`	`i=0;`
`@@ -1415,10 +1416,10 @@ pg_next_dst_boundary(const pg_time_t *timep,`
`1415`	`1416`	`*after_isdst=ttisp->tt_isdst;`
`1416`	`1417`	`return1;`
`1417`	`1418`	`}`
`1418`		`-/* Else search to find thecontaining segment */`
	`1419`	`+/* Else search to find theboundary following t */`
`1419`	`1420`	`{`
`1420`	`1421`	`intlo=1;`
`1421`		`-inthi=sp->timecnt;`
	`1422`	`+inthi=sp->timecnt-1;`
`1422`	`1423`
`1423`	`1424`	`while (lo<hi)`
`1424`	`1425`	`{`

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`‎src/timezone/localtime.c`

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