fat: Fix and cleanup timestamp conversion

This cleans date_dos2unix()/fat_date_unix2dos() up. New code should be
much more readable.

And this fixes those old functions. Those doesn't handle 2100
correctly. 2100 isn't leap year, but old one handles it as leap year.
Also, with this, centi sec is handled and is fixed.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 107 insertions, 41 deletions

diff --git a/fs/fat/misc.c b/fs/fat/misc.c
index 91ad9be18ff9..a191e79e66a9 100644
--- a/fs/fat/misc.c
+++ b/fs/fat/misc.c
@@ -135,65 +135,131 @@ int fat_chain_add(struct inode *inode, int new_dclus, int nr_cluster)
 
 extern struct timezone sys_tz;
 
+/*
+ * The epoch of FAT timestamp is 1980.
+ *     :  bits :     value
+ * date:  0 -  4: day   (1 -  31)
+ * date:  5 -  8: month (1 -  12)
+ * date:  9 - 15: year  (0 - 127) from 1980
+ * time:  0 -  4: sec   (0 -  29) 2sec counts
+ * time:  5 - 10: min   (0 -  59)
+ * time: 11 - 15: hour  (0 -  23)
+ */
+#define SECS_PER_MIN    60
+#define SECS_PER_HOUR   (60 * 60)
+#define SECS_PER_DAY    (SECS_PER_HOUR * 24)
+#define UNIX_SECS_1980  315532800L
+#if BITS_PER_LONG == 64
+#define UNIX_SECS_2108  4354819200L
+#endif
+/* days between 1.1.70 and 1.1.80 (2 leap days) */
+#define DAYS_DELTA      (365 * 10 + 2)
+/* 120 (2100 - 1980) isn't leap year */
+#define YEAR_2100       120
+#define IS_LEAP_YEAR(y) (!((y) & 3) && (y) != YEAR_2100)
+
 /* Linear day numbers of the respective 1sts in non-leap years. */
-static int day_n[] = {
-   /* Jan  Feb  Mar  Apr   May  Jun  Jul  Aug  Sep  Oct  Nov  Dec */
-        0,  31,  59,  90,  120, 151, 181, 212, 243, 273, 304, 334, 0, 0, 0, 0
+static time_t days_in_year[] = {
+        /* Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec */
+        0,   0,  31,  59,  90, 120, 151, 181, 212, 243, 273, 304, 334, 0, 0, 0,
 };
 
-/* Convert a MS-DOS time/date pair to a UNIX date (seconds since 1 1 70). */
-int date_dos2unix(unsigned short time, unsigned short date, int tz_utc)
+/* Convert a FAT time/date pair to a UNIX date (seconds since 1 1 70). */
+void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec *ts,
+                       __le16 __time, __le16 __date, u8 time_cs)
 {
-        int month, year, secs;
+        u16 time = le16_to_cpu(__time), date = le16_to_cpu(__date);
+        time_t second, day, leap_day, month, year;
 
-        /*
-         * first subtract and mask after that... Otherwise, if
-         * date == 0, bad things happen
-         */
-        month = ((date >> 5) - 1) & 15;
-        year = date >> 9;
-        secs = (time & 31)*2+60*((time >> 5) & 63)+(time >> 11)*3600+86400*
-            ((date & 31)-1+day_n[month]+(year/4)+year*365-((year & 3) == 0 &&
-            month < 2 ? 1 : 0)+3653);
-                        /* days since 1.1.70 plus 80's leap day */
-        if (!tz_utc)
-                secs += sys_tz.tz_minuteswest*60;
-        return secs;
+        year  = date >> 9;
+        month = max(1, (date >> 5) & 0xf);
+        day   = max(1, date & 0x1f) - 1;
+
+        leap_day = (year + 3) / 4;
+        if (year > YEAR_2100)           /* 2100 isn't leap year */
+                leap_day--;
+        if (IS_LEAP_YEAR(year) && month > 2)
+                leap_day++;
+
+        second =  (time & 0x1f) << 1;
+        second += ((time >> 5) & 0x3f) * SECS_PER_MIN;
+        second += (time >> 11) * SECS_PER_HOUR;
+        second += (year * 365 + leap_day
+                   + days_in_year[month] + day
+                   + DAYS_DELTA) * SECS_PER_DAY;
+
+        if (!sbi->options.tz_utc)
+                second += sys_tz.tz_minuteswest * SECS_PER_MIN;
+
+        if (time_cs) {
+                ts->tv_sec = second + (time_cs / 100);
+                ts->tv_nsec = (time_cs % 100) * 10000000;
+        } else {
+                ts->tv_sec = second;
+                ts->tv_nsec = 0;
+        }
 }
 
-/* Convert linear UNIX date to a MS-DOS time/date pair. */
-void fat_date_unix2dos(int unix_date, __le16 *time, __le16 *date, int tz_utc)
+/* Convert linear UNIX date to a FAT time/date pair. */
+void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec *ts,
+                       __le16 *time, __le16 *date, u8 *time_cs)
 {
-        int day, year, nl_day, month;
+        time_t second = ts->tv_sec;
+        time_t day, leap_day, month, year;
 
-        if (!tz_utc)
-                unix_date -= sys_tz.tz_minuteswest*60;
+        if (!sbi->options.tz_utc)
+                second -= sys_tz.tz_minuteswest * SECS_PER_MIN;
 
         /* Jan 1 GMT 00:00:00 1980. But what about another time zone? */
-        if (unix_date < 315532800)
-                unix_date = 315532800;
-
-        *time = cpu_to_le16((unix_date % 60)/2+(((unix_date/60) % 60) << 5)+
-            (((unix_date/3600) % 24) << 11));
-        day = unix_date/86400-3652;
-        year = day/365;
-        if ((year+3)/4+365*year > day)
+        if (second < UNIX_SECS_1980) {
+                *time = 0;
+                *date = cpu_to_le16((0 << 9) | (1 << 5) | 1);
+                if (time_cs)
+                        *time_cs = 0;
+                return;
+        }
+#if BITS_PER_LONG == 64
+        if (second >= UNIX_SECS_2108) {
+                *time = cpu_to_le16((23 << 11) | (59 << 5) | 29);
+                *date = cpu_to_le16((127 << 9) | (12 << 5) | 31);
+                if (time_cs)
+                        *time_cs = 199;
+                return;
+        }
+#endif
+
+        day = second / SECS_PER_DAY - DAYS_DELTA;
+        year = day / 365;
+        leap_day = (year + 3) / 4;
+        if (year > YEAR_2100)           /* 2100 isn't leap year */
+                leap_day--;
+        if (year * 365 + leap_day > day)
                 year--;
-        day -= (year+3)/4+365*year;
-        if (day == 59 && !(year & 3)) {
-                nl_day = day;
+        leap_day = (year + 3) / 4;
+        if (year > YEAR_2100)           /* 2100 isn't leap year */
+                leap_day--;
+        day -= year * 365 + leap_day;
+
+        if (IS_LEAP_YEAR(year) && day == days_in_year[3]) {
                 month = 2;
         } else {
-                nl_day = (year & 3) || day <= 59 ? day : day-1;
-                for (month = 0; month < 12; month++) {
-                        if (day_n[month] > nl_day)
+                if (IS_LEAP_YEAR(year) && day > days_in_year[3])
+                        day--;
+                for (month = 1; month < 12; month++) {
+                        if (days_in_year[month + 1] > day)
                                 break;
                 }
         }
-        *date = cpu_to_le16(nl_day-day_n[month-1]+1+(month << 5)+(year << 9));
-}
+        day -= days_in_year[month];
 
-EXPORT_SYMBOL_GPL(fat_date_unix2dos);
+        *time = cpu_to_le16(((second / SECS_PER_HOUR) % 24) << 11
+                            | ((second / SECS_PER_MIN) % 60) << 5
+                            | (second % SECS_PER_MIN) >> 1);
+        *date = cpu_to_le16((year << 9) | (month << 5) | (day + 1));
+        if (time_cs)
+                *time_cs = (ts->tv_sec & 1) * 100 + ts->tv_nsec / 10000000;
+}
+EXPORT_SYMBOL_GPL(fat_time_unix2fat);
 
 int fat_sync_bhs(struct buffer_head **bhs, int nr_bhs)
 {