limine/common/lib/time.c

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#include <stddef.h>
#include <stdint.h>
#include <lib/time.h>
#if defined (BIOS)
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# include <lib/real.h>
#elif defined (UEFI)
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# include <efi.h>
#endif
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#include <lib/misc.h>
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// Julian date calculation from https://en.wikipedia.org/wiki/Julian_day
static uint64_t get_jdn(uint8_t days, uint8_t months, uint16_t years) {
return (1461 * (years + 4800 + (months - 14)/12))/4 + (367 *
(months - 2 - 12 * ((months - 14)/12)))/12 -
(3 * ((years + 4900 + (months - 14)/12)/100))/4
+ days - 32075;
}
static uint64_t get_unix_epoch(uint8_t seconds, uint8_t minutes, uint8_t hours,
uint8_t days, uint8_t months, uint16_t years) {
uint64_t jdn_current = get_jdn(days, months, years);
uint64_t jdn_1970 = get_jdn(1, 1, 1970);
uint64_t jdn_diff = jdn_current - jdn_1970;
return (jdn_diff * (60 * 60 * 24)) + hours * 3600 + minutes * 60 + seconds;
}
#if defined (BIOS)
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uint64_t time(void) {
struct rm_regs r;
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again:
r = (struct rm_regs){0};
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r.eax = 0x0400;
rm_int(0x1a, &r, &r);
uint8_t day = bcd_to_int( r.edx & 0x00ff);
uint8_t month = bcd_to_int((r.edx & 0xff00) >> 8);
uint16_t year = bcd_to_int( r.ecx & 0x00ff) +
/* century */ bcd_to_int((r.ecx & 0xff00) >> 8) * 100;
r = (struct rm_regs){0};
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r.eax = 0x0200;
rm_int(0x1a, &r, &r);
uint8_t second = bcd_to_int((r.edx & 0xff00) >> 8);
uint8_t minute = bcd_to_int( r.ecx & 0x00ff);
uint8_t hour = bcd_to_int((r.ecx & 0xff00) >> 8);
// Check RTC day wraparound
r = (struct rm_regs){0};
r.eax = 0x0400;
rm_int(0x1a, &r, &r);
if (bcd_to_int(r.edx & 0x00ff) != day) {
goto again;
}
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return get_unix_epoch(second, minute, hour, day, month, year);
}
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#endif
#if defined (UEFI)
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uint64_t time(void) {
EFI_TIME time;
gRT->GetTime(&time, NULL);
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return get_unix_epoch(time.Second, time.Minute, time.Hour,
time.Day, time.Month, time.Year);
}
#endif