mirror of https://github.com/cc65/cc65.git
130 lines
3.3 KiB
ArmAsm
130 lines
3.3 KiB
ArmAsm
;
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; Colin Leroy-Mira, 2024
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;
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; struct tm* __fastcall__ _time_t_to_tm (const time_t t)
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;
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; Helper to gmtime and localtime. Breaks down a number of
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; seconds since Jan 1, 1970 into days, hours and seconds,
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; so that each of them fits in 16 bits; passes the
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; result to _mktime which fixes all values in the struct,
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; and returns a pointer to the struct to callers.
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;
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.export __time_t_to_tm
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.import udiv32, _mktime
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.importzp sreg, tmp3, ptr1, ptr2, ptr3, ptr4
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.include "time.inc"
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.macpack cpu
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__time_t_to_tm:
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; Divide number of seconds since epoch, in ptr1:sreg,
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; by 86400 to get the number of days since epoch, and
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; the number of seconds today in the remainder.
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; Load t as dividend (sreg is already set by the caller)
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sta ptr1
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stx ptr1+1
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; Load 86400 as divisor
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lda #$80
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sta ptr3
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lda #$51
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sta ptr3+1
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lda #$01
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sta ptr4
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lda #$00
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sta ptr4+1
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; Clear TM buf while we have zero in A
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ldx #.sizeof(tm)-1
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: sta TM,x
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dex
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bpl :-
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; Divide t/86400
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jsr udiv32
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; Store the quotient (the number of full days), and increment
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; by one as epoch starts at day 1.
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clc
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lda ptr1
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adc #1
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sta TM + tm::tm_mday
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lda ptr1+1
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adc #0
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sta TM + tm::tm_mday+1
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; Now divide the number of remaining seconds by 3600,
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; to get the number of hours, and the seconds in the
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; current hour, in neat 16-bit integers.
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; Load the previous division's remainder (in ptr2:tmp3:tmp4)
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; as dividend
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lda ptr2
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sta ptr1
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lda ptr2+1
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sta ptr1+1
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lda tmp3
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sta sreg
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; We ignore the high byte stored in tmp4 because it will be
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; zero. We'll zero sreg+1 right below, when we'll have
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; a convenient zero already in A.
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; Load divisor
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lda #<3600
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sta ptr3
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lda #>3600
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sta ptr3+1
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; Zero the two high bytes of the divisor and the high byte
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; of the dividend.
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.if .cpu .bitand CPU_ISET_65SC02
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stz ptr4
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stz ptr4+1
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stz sreg+1
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.else
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lda #$00
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sta ptr4
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sta ptr4+1
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sta sreg+1
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.endif
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; Do the division
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jsr udiv32
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; Store year
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lda #70
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sta TM + tm::tm_year
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; Store hours (the quotient of the last division)
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lda ptr1
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sta TM + tm::tm_hour
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lda ptr1+1
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sta TM + tm::tm_hour+1
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; Store seconds (the remainder of the last division)
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lda ptr2
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sta TM + tm::tm_sec
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lda ptr2+1
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sta TM + tm::tm_sec+1
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; The rest of the struct tm fields are zero. mktime
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; will take care of shifting extra seconds to minutes,
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; and extra days to months and years.
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; Call mktime
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lda #<TM
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ldx #>TM
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jsr _mktime
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; And return our pointer
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lda #<TM
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ldx #>TM
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rts
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.bss
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TM: .tag tm
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