support setting file date/time from dos

1 files changed, 64 insertions, 0 deletions

diff --git a/unixtime.h b/unixtime.h
index 296c8ac..57846b7 100644
--- a/unixtime.h
+++ b/unixtime.h
@@ -150,4 +150,68 @@ static void timestampns_to_dos_time(uint16_t __far *dos_time, uint16_t __far *do
 	*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);
+
+	dlog_print("days_since_epoch=");
+	dlog_printd(days_since_epoch);
+	dlog_print(" seconds2_since_day=");
+	dlog_printd(seconds2_since_day);
+	dlog_endline();
+
+	__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