Prevent localtime() from potentially giving incorrect tm_isdst values.

This could happen when it was called for a time other than the present, because it set tm_isdst based on the current value of the DST flag in BRAM, which is valid only for the current time.

Now it works as follows: If localtime() is passed the time_t value that was produced by the most recent call to time(), it gives the DST setting in effect at the time of that call.  Otherwise, it sets tm_isdst to -1, indicating that the correct value is unknown.

This is about the best we can do without having a full timezone library/database. It should give the right tm_isdst value in probably the most common case, and avoids giving an incorrect value in any case (assuming the system's DST flag is right).

This fixes #18.
This commit is contained in:
Stephen Heumann 2020-02-02 12:51:58 -06:00
parent 9af1c093cb
commit 44dfc1d1d6

View File

@ -41,6 +41,9 @@ second ds 4 second 0..59
count ds 4 seconds since 1 Jan 1970
t1 ds 4 work variable
t2 ds 4 work variable
lasttime ds 4 last time_t value returned by time()
lastDST dc i2'-1' tm_isdst value for lasttime
end
****************************************************************
@ -284,6 +287,15 @@ gmtime entry
lda [t]
sta t
stx t+2
ldy #-1 default DST setting = -1 (unknown)
cmp lasttime determine DST setting, if we can
bne lb0
cpx lasttime+2
bne lb0
ldy lastDST
lb0 sty tm_isdst
lda #69 find the year
sta year
lda #1
@ -340,15 +352,6 @@ lb2a ble lb2
sta tm_mday
ph4 #tm_sec set the day of week/year
jsl mktime
pha determine if it's daylight savings
ph2 #$5E
_ReadBParam
pla
lsr A
and #$0001
eor #$0001
sta tm_isdst
lla t,tm_sec
plb
creturn 4:t
@ -499,7 +502,20 @@ time start
lda count+2
sta [tptr],Y
lb1 move4 count,tptr
lb1 lda count
sta tptr
sta lasttime
lda count+2
sta tptr+2
sta lasttime+2
pha determine if it's daylight savings
ph2 #$5E
_ReadBParam
pla
lsr A
and #$0001
eor #$0001
sta lastDST
plb
creturn 4:tptr
end