[PATCH v2 1/2] datetime: Support dates outside of 1901..2038 range

* [PATCH v2 1/2] datetime: Support dates outside of 1901..2038 range
@ 2024-08-17 17:30 Vladimir Serbinenko
  2024-08-17 17:30 ` [PATCH v2 2/2] date_unit_test: test dates outside of 32-bit unix range Vladimir Serbinenko
                   ` (2 more replies)
  0 siblings, 3 replies; 9+ messages in thread
From: Vladimir Serbinenko @ 2024-08-17 17:30 UTC (permalink / raw)
  To: grub-devel; +Cc: Vladimir Serbinenko

Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
---
 grub-core/lib/datetime.c | 31 ++++++++++++++++++++++++-------
 include/grub/datetime.h  | 15 +++++++--------
 2 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/grub-core/lib/datetime.c b/grub-core/lib/datetime.c
index 9120128ca..e4bdc5c4f 100644
--- a/grub-core/lib/datetime.c
+++ b/grub-core/lib/datetime.c
@@ -59,6 +59,8 @@ grub_get_weekday_name (struct grub_datetime *datetime)
 #define SECPERDAY (24*SECPERHOUR)
 #define DAYSPERYEAR 365
 #define DAYSPER4YEARS (4*DAYSPERYEAR+1)
+#define DAYSPER100YEARS (100*DAYSPERYEAR+24)
+#define DAYSPER400YEARS (400*DAYSPERYEAR+97)
 
 
 void
@@ -71,7 +73,7 @@ grub_unixtime2datetime (grub_int64_t nix, struct grub_datetime *datetime)
   /* Convenience: let's have 3 consecutive non-bissextile years
      at the beginning of the counting date. So count from 1901. */
   int days_epoch;
-  /* Number of days since 1st Januar, 1901.  */
+  /* Number of days since 1st January, 1 (proleptic).  */
   unsigned days;
   /* Seconds into current day.  */
   unsigned secs_in_day;
@@ -87,9 +89,25 @@ grub_unixtime2datetime (grub_int64_t nix, struct grub_datetime *datetime)
     days_epoch = grub_divmod64 (nix, SECPERDAY, NULL);
 
   secs_in_day = nix - days_epoch * SECPERDAY;
-  days = days_epoch + 69 * DAYSPERYEAR + 17;
+  days = days_epoch + 369 * DAYSPERYEAR + 17 + 24 * 3 + 4 * DAYSPER400YEARS;
 
-  datetime->year = 1901 + 4 * (days / DAYSPER4YEARS);
+  datetime->year = 1 + 400 * (days / DAYSPER400YEARS);
+  days %= DAYSPER400YEARS;
+
+  /* On 31st December of bissextile years 365 days from the beginning
+     of the year elapsed but year isn't finished yet */
+  if (days / DAYSPER100YEARS == 4)
+    {
+      datetime->year += 396;
+      days -= 396*DAYSPERYEAR + 96;
+    }
+  else
+    {
+      datetime->year += 100 * (days / DAYSPER100YEARS);
+      days %= DAYSPER100YEARS;
+    }
+
+  datetime->year += 4 * (days / DAYSPER4YEARS);
   days %= DAYSPER4YEARS;
   /* On 31st December of bissextile years 365 days from the beginning
      of the year elapsed but year isn't finished yet */
@@ -103,11 +121,10 @@ grub_unixtime2datetime (grub_int64_t nix, struct grub_datetime *datetime)
       datetime->year += days / DAYSPERYEAR;
       days %= DAYSPERYEAR;
     }
+  int isbisextile = datetime->year % 4 == 0 && (datetime->year % 100 != 0 || datetime->year % 400 == 0);
   for (i = 0; i < 12
-	 && days >= (i==1 && datetime->year % 4 == 0
-		      ? 29 : months[i]); i++)
-    days -= (i==1 && datetime->year % 4 == 0
-			    ? 29 : months[i]);
+	 && days >= (i==1 && isbisextile ? 29 : months[i]); i++)
+    days -= (i==1 && isbisextile ? 29 : months[i]);
   datetime->month = i + 1;
   datetime->day = 1 + days;
   datetime->hour = (secs_in_day / SECPERHOUR);
diff --git a/include/grub/datetime.h b/include/grub/datetime.h
index bcec636f0..9289b0d00 100644
--- a/include/grub/datetime.h
+++ b/include/grub/datetime.h
@@ -54,7 +54,7 @@ void grub_unixtime2datetime (grub_int64_t nix,
 static inline int
 grub_datetime2unixtime (const struct grub_datetime *datetime, grub_int64_t *nix)
 {
-  grub_int32_t ret;
+  grub_int64_t ret;
   int y4, ay;
   const grub_uint16_t monthssum[12]
     = { 0,
@@ -75,15 +75,11 @@ grub_datetime2unixtime (const struct grub_datetime *datetime, grub_int64_t *nix)
   const int SECPERHOUR = 60 * SECPERMIN;
   const int SECPERDAY = 24 * SECPERHOUR;
   const int SECPERYEAR = 365 * SECPERDAY;
-  const int SECPER4YEARS = 4 * SECPERYEAR + SECPERDAY;
+  const grub_int64_t SECPER4YEARS = 4 * SECPERYEAR + SECPERDAY;
 
-  if (datetime->year > 2038 || datetime->year < 1901)
-    return 0;
   if (datetime->month > 12 || datetime->month < 1)
     return 0;
 
-  /* In the period of validity of unixtime all years divisible by 4
-     are bissextile*/
   /* Convenience: let's have 3 consecutive non-bissextile years
      at the beginning of the epoch. So count from 1973 instead of 1970 */
   ret = 3 * SECPERYEAR + SECPERDAY;
@@ -94,13 +90,16 @@ grub_datetime2unixtime (const struct grub_datetime *datetime, grub_int64_t *nix)
   ret += y4 * SECPER4YEARS;
   ret += ay * SECPERYEAR;
 
+  ret -= ((datetime->year - 1) / 100 - (datetime->year - 1) / 400 - 15) * SECPERDAY;
+
   ret += monthssum[datetime->month - 1] * SECPERDAY;
-  if (ay == 3 && datetime->month >= 3)
+  int isbisextile = ay == 3 && (datetime->year % 100 != 0 || datetime->year % 400 == 0);
+  if (isbisextile && datetime->month >= 3)
     ret += SECPERDAY;
 
   ret += (datetime->day - 1) * SECPERDAY;
   if ((datetime->day > months[datetime->month - 1]
-       && (!ay || datetime->month != 2 || datetime->day != 29))
+       && !(isbisextile && datetime->month == 2 && datetime->day == 29))
       || datetime->day < 1)
     return 0;
 
-- 
2.39.2


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