On Mon, Aug 25, 2025 at 10:17:37PM -0500, Andrew Hamilton wrote:
> Support dates outside of 1901..2038.
>
> Fixes: https://savannah.gnu.org/bugs/?63894
> Fixes: https://savannah.gnu.org/bugs/?66301
>
> Signed-off-by: Vladimir Serbinenko <[email protected]>
> Signed-off-by: Andrew Hamilton <[email protected]>
> ---
> grub-core/lib/datetime.c | 64 ++++++++++++++++++++++++++++++++--------
> include/grub/datetime.h | 27 ++++++++++++-----
> 2 files changed, 71 insertions(+), 20 deletions(-)
>
> diff --git a/grub-core/lib/datetime.c b/grub-core/lib/datetime.c
> index 8f0922fb0..a0f84d989 100644
> --- a/grub-core/lib/datetime.c
> +++ b/grub-core/lib/datetime.c
> @@ -64,7 +64,10 @@ grub_get_weekday_name (struct grub_datetime *datetime)
> #define SECPERDAY (24*SECPERHOUR)
> #define DAYSPERYEAR 365
> #define DAYSPER4YEARS (4*DAYSPERYEAR+1)
> -
> +/* 24 leap years in 100 years */
> +#define DAYSPER100YEARS (100 * DAYSPERYEAR + 24)
> +/* 97 leap years in 400 years */
> +#define DAYSPER400YEARS (400 * DAYSPERYEAR + 97)
>
> void
> grub_unixtime2datetime (grub_int64_t nix, struct grub_datetime *datetime)
> @@ -76,10 +79,12 @@ 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;
> + /* Tracks whether this is a leap year. */
> + bool is_bisextile;
>
> /* Transform C divisions and modulos to mathematical ones */
> if (nix < 0)
> @@ -92,27 +97,62 @@ 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;
> + /*
> + * 1970 is Unix Epoch. Adjust to a year 1 epoch:
> + * Leap year logic:
> + * - Years evenly divisible by 400 are leap years
> + * - Otherwise, if divisible by 100 are not leap years
> + * - Otherwise, if divisible by 4 are leap years
> + * There are four 400-year periods (1600 years worth of days with leap
> days)
> + * There are three 100-year periods worth of leap days (3*24)
> + * There are 369 years in addition to the four 400 year periods
> + * There are 17 leap days in 69 years (beyond the three 100 year periods)
> + */
> + days = days_epoch + 369 * DAYSPERYEAR + 17 + 24 * 3 + 4 * DAYSPER400YEARS;
> +
> + datetime->year = 1 + 400 * (days / DAYSPER400YEARS);
> + days %= DAYSPER400YEARS;
>
> - datetime->year = 1901 + 4 * (days / DAYSPER4YEARS);
> + /*
> + * On 31st December of bissextile (leap) years 365 days from the beginning
> + * of the year elapsed but year isn't finished yet - every 400 years
> + * 396 is 4 years less than 400 year leap cycle
> + * 96 is 1 day less than number of leap days in 400 years
> + */
> + 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 */
> + /*
> + * On 31st December of bissextile (leap) years 365 days from the beginning
> + * of the year elapsed but year isn't finished yet - every 4 years
> + */
> if (days / DAYSPERYEAR == 4)
> {
> datetime->year += 3;
> - days -= 3*DAYSPERYEAR;
> + days -= 3 * DAYSPERYEAR;
> }
> else
> {
> datetime->year += days / DAYSPERYEAR;
> days %= DAYSPERYEAR;
> }
> - 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]);
> +
> + is_bisextile = datetime->year % 4 == 0
> + && (datetime->year % 100 != 0 || datetime->year % 400 == 0);
Even if it works it is not fully correct...
is_bisextile = (datetime->year % 4 == 0 &&
(datetime->year % 100 != 0 || datetime->year % 400 == 0)) ?
true : false;
> + for (i = 0;
> + i < 12 && days >= ((i == 1 && is_bisextile == true) ? 29 : months[i]);
> + i++)
> + days -= ((i == 1 && is_bisextile == true) ? 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..ff847e847 100644
> --- a/include/grub/datetime.h
> +++ b/include/grub/datetime.h
> @@ -54,8 +54,9 @@ 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;
> + bool is_bisextile;
> const grub_uint16_t monthssum[12]
> = { 0,
> 31,
> @@ -75,15 +76,11 @@ 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 +91,27 @@ grub_datetime2unixtime (const struct grub_datetime
> *datetime, grub_int64_t *nix)
> ret += y4 * SECPER4YEARS;
> ret += ay * SECPERYEAR;
>
> + /*
> + * Correct above calculation (which assumes every 4 years is a leap year)
> + * to remove those "false leap years" that are divisible by 100 but not
> 400.
> + * Since this logic starts with seconds since 1973, 15 is used because:
> + * - (1973 - 1) / 100 = 19 (floor due to integer math)
> + * - (1973 - 1) / 400 = 4 (floor due to integer math)
> + * - 19 - 4 - 15 = 0 (we want to start with no "false leap years" at time
> + * zero of 1973)
> + */
> + ret -= ((datetime->year - 1) / 100 - (datetime->year - 1) / 400 - 15)
> + * SECPERDAY;
> +
> ret += monthssum[datetime->month - 1] * SECPERDAY;
> - if (ay == 3 && datetime->month >= 3)
> + is_bisextile = ay == 3
> + && (datetime->year % 100 != 0 || datetime->year % 400 == 0);
Again...
is_bisextile = (ay == 3 && (datetime->year % 100 != 0 || datetime->year % 400
== 0)) ? true : false;
> + if (is_bisextile && datetime->month >= 3)
is_bisextile == true && ...
> ret += SECPERDAY;
>
> ret += (datetime->day - 1) * SECPERDAY;
> if ((datetime->day > months[datetime->month - 1]
> - && (!ay || datetime->month != 2 || datetime->day != 29))
> + && !(is_bisextile && datetime->month == 2 && datetime->day == 29))
is_bisextile == true && ...
... and I would drop "is_" from variable name...
Daniel
_______________________________________________
Grub-devel mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/grub-devel
