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/*
* VBSF - unix to DOS time conversion
* Copyright (C) 2022 Javier S. Pedro
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#ifndef UNIXTIME_H
#define UNIXTIME_H
#include <stdbool.h>
#include <stdint.h>
#include "dlog.h"
#define UNIX_EPOCH_YEAR 1970
#define DOS_EPOCH_YEAR 1980
static bool is_leap_year(unsigned year)
{
return ((year % 4) == 0 && (year % 100) != 0 || (year % 400) == 0);
}
static int days_per_year(unsigned year)
{
return is_leap_year(year) ? 366 : 365;
}
static int days_per_month(unsigned month, bool leapyear)
{
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
return 31;
case 4:
case 6:
case 9:
case 11:
return 30;
case 2:
return leapyear ? 29 : 28;
}
return 0;
}
static void timestampns_to_dos_time(uint16_t __far *dos_time, uint16_t __far *dos_date, int64_t timestampns, int32_t tzoffset)
{
// To maximize range of 32-bit ints, we'll use DOS's "2 seconds" as a unit instead of 1 second
long days_since_epoch = 0;
unsigned hours = 0, minutes = 0, seconds2 = 0;
unsigned year, month, day;
int per_year, per_month;
bool is_leap;
// Since we can only run on >= 386 anyway, let's do the initial
// 64-bit division and the rest of 32-bit divisions/modulos
// in asm using 386 32-bit instructions.
__asm {
push eax /* Preserve 32-bit regs */
push ecx
push edx
mov eax, dword ptr [timestampns]
mov edx, dword ptr [timestampns + 4]
mov ecx, 2 * 1000000000 /* nanoseconds in 2 seconds, should still fit in a dword */
idiv ecx /* 64-bit signed divison edx:eax / ecx, returns quotient in eax, remainder in edx */
/* TODO: Handle overflow, which will trigger an interrupt */
/* eax now contains seconds_since_epoch / 2 */
xor edx, edx /* Discard the remainder (less than 2 seconds) */
sub eax, [tzoffset] /* Subtract tzoffset now (which is in seconds / 2 units) */
mov ecx, (24 * 60 * 60) / 2 /* seconds in one day / 2 */
idiv ecx
/* eax now contains days_since_epoch */
/* edx contains seconds (since start of day) /2 , this now fits in a 16-bit word */
mov [days_since_epoch], eax
mov eax, edx /* eax = seconds / 2 */
xor edx, edx
mov ecx, 60 / 2 /* seconds in a minute / 2; also clears upper part of ecx, we'll start using 16-bit registers from now on */
div cx
/* ax contains minutes, dx contains remainder seconds/2 -- should be < 30 */
mov [seconds2], dx
xor dx, dx
mov cx, 60 /* minutes per hour */
div cx
/* ax contains hours (< 24), dx contains remainder minutes (< 60) */
mov [minutes], dx
mov [hours], ax
pop edx
pop ecx
pop eax
}
year = UNIX_EPOCH_YEAR;
if (days_since_epoch > 0) {
while (days_since_epoch >= (per_year = days_per_year(year))) {
days_since_epoch -= per_year;
year++;
}
} else {
while (days_since_epoch < 0) {
days_since_epoch += days_per_year(year);
year--;
}
}
month = 1;
is_leap = is_leap_year(year);
while (days_since_epoch >= (per_month = days_per_month(month, is_leap))) {
days_since_epoch -= per_month;
month++;
}
day = 1 + days_since_epoch; // (day is 1-based)
if (year < DOS_EPOCH_YEAR) {
dputs("Year is too old, will show as 0");
year = 0;
} else {
year -= DOS_EPOCH_YEAR;
}
*dos_time = ((hours << 11) & 0xF800) | ((minutes << 5) & 0x7E0) | (seconds2 & 0x1F);
*dos_date = ((year << 9) & 0xFE00) | ((month << 5) & 0x1E0) | (day & 0x1F);
}
static void timestampns_from_dos_time(int64_t *timestampns, uint16_t dos_time, uint16_t dos_date, int32_t tzoffset)
{
unsigned year = (dos_date & 0xFE00) >> 9,
month = (dos_date & 0x1E0) >> 5,
day = (dos_date & 0x1F),
hours = (dos_time & 0xF800) >> 11,
minutes = (dos_time & 0x7E0) >> 5,
seconds2 = (dos_time & 0x1F);
long days_since_epoch = 0;
long seconds2_since_day;
bool is_leap;
year += DOS_EPOCH_YEAR;
is_leap = is_leap_year(year);
while (year > UNIX_EPOCH_YEAR) {
days_since_epoch += days_per_year(--year);
}
while (year < UNIX_EPOCH_YEAR) {
days_since_epoch -= days_per_year(year++);
}
while (month > 1) {
days_since_epoch += days_per_month(--month, is_leap);
}
days_since_epoch += day - 1;
seconds2_since_day = seconds2 + (minutes * 60U/2) + (hours * 3600U/2);
__asm {
push eax
push ecx
push edx
mov eax, [days_since_epoch]
mov ecx, (24 * 60 * 60) / 2 /* seconds in one day / 2 */
imul eax, ecx
add eax, [seconds2_since_day]
/* eax now contains seconds_since_epoch / 2 */
add eax, [tzoffset] /* Add tzoffset now (which is in seconds / 2 units) */
mov ecx, 2 * 1000000000 /* nanoseconds in 2 seconds, should still fit in a dword */
imul ecx /* 64-bit signed multiply eax * ecx, returns result in edx:eax */
mov si, [timestampns]
mov dword ptr [si], eax
mov dword ptr [si + 4], edx
pop edx
pop ecx
pop eax
}
}
#endif // UNIXTIME_H
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