gmtime_r: Use faster algorithm by Howard Hinnant
* libc/time/gmtime_r.c (gmtime_r): use faster algorithm from civil_from_days() by Howard Hinnant Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Freddie Chopin
Corinna Vinschen
parent
b81a830f1a
commit
325926031b
|
|
@ -1,3 +1,8 @@
|
|||
2015-06-15 Freddie Chopin <freddie_chopin@op.pl>
|
||||
|
||||
* libc/time/gmtime_r.c (gmtime_r): use faster algorithm from
|
||||
civil_from_days() by Howard Hinnant
|
||||
|
||||
2015-06-01 Hale Wang <hale.wang@arm.com>
|
||||
|
||||
* libc/machine/arm/aeabi_memmove-arm.S (__aeabi_memmove): Update the
|
||||
|
|
|
|||
|
|
@ -9,6 +9,8 @@
|
|||
* - Fixed bug in calculations for dates after year 2069 or before year 1901. Ideas for
|
||||
* solution taken from musl's __secs_to_tm() - 07/12/2014, Freddie Chopin
|
||||
* <freddie_chopin@op.pl>
|
||||
* - Use faster algorithm from civil_from_days() by Howard Hinnant - 12/06/2014,
|
||||
* Freddie Chopin <freddie_chopin@op.pl>
|
||||
*
|
||||
* Converts the calendar time pointed to by tim_p into a broken-down time
|
||||
* expressed as local time. Returns a pointer to a structure containing the
|
||||
|
|
@ -17,20 +19,21 @@
|
|||
|
||||
#include "local.h"
|
||||
|
||||
/* move epoch from 01.01.1970 to 01.03.2000 - this is the first day of new
|
||||
* 400-year long cycle, right after additional day of leap year. This adjustment
|
||||
* is required only for date calculation, so instead of modifying time_t value
|
||||
* (which would require 64-bit operations to work correctly) it's enough to
|
||||
* adjust the calculated number of days since epoch. */
|
||||
#define EPOCH_ADJUSTMENT_DAYS 11017
|
||||
/* Move epoch from 01.01.1970 to 01.03.0000 (yes, Year 0) - this is the first
|
||||
* day of a 400-year long "era", right after additional day of leap year.
|
||||
* This adjustment is required only for date calculation, so instead of
|
||||
* modifying time_t value (which would require 64-bit operations to work
|
||||
* correctly) it's enough to adjust the calculated number of days since epoch.
|
||||
*/
|
||||
#define EPOCH_ADJUSTMENT_DAYS 719468L
|
||||
/* year to which the adjustment was made */
|
||||
#define ADJUSTED_EPOCH_YEAR 2000
|
||||
/* 1st March of 2000 is Wednesday */
|
||||
#define ADJUSTED_EPOCH_YEAR 0
|
||||
/* 1st March of year 0 is Wednesday */
|
||||
#define ADJUSTED_EPOCH_WDAY 3
|
||||
/* there are 97 leap years in 400-year periods. ((400 - 97) * 365 + 97 * 366) */
|
||||
#define DAYS_PER_400_YEARS 146097L
|
||||
#define DAYS_PER_ERA 146097L
|
||||
/* there are 24 leap years in 100-year periods. ((100 - 24) * 365 + 24 * 366) */
|
||||
#define DAYS_PER_100_YEARS 36524L
|
||||
#define DAYS_PER_CENTURY 36524L
|
||||
/* there is one leap year every 4 years */
|
||||
#define DAYS_PER_4_YEARS (3 * 365 + 366)
|
||||
/* number of days in a non-leap year */
|
||||
|
|
@ -39,6 +42,8 @@
|
|||
#define DAYS_IN_JANUARY 31
|
||||
/* number of days in non-leap February */
|
||||
#define DAYS_IN_FEBRUARY 28
|
||||
/* number of years per era */
|
||||
#define YEARS_PER_ERA 400
|
||||
|
||||
struct tm *
|
||||
_DEFUN (gmtime_r, (tim_p, res),
|
||||
|
|
@ -47,12 +52,11 @@ _DEFUN (gmtime_r, (tim_p, res),
|
|||
{
|
||||
long days, rem;
|
||||
_CONST time_t lcltime = *tim_p;
|
||||
int year, month, yearday, weekday;
|
||||
int years400, years100, years4, remainingyears;
|
||||
int yearleap;
|
||||
_CONST int *ip;
|
||||
int era, weekday, year;
|
||||
unsigned erayear, yearday, month, day;
|
||||
unsigned long eraday;
|
||||
|
||||
days = ((long)lcltime) / SECSPERDAY - EPOCH_ADJUSTMENT_DAYS;
|
||||
days = ((long)lcltime) / SECSPERDAY + EPOCH_ADJUSTMENT_DAYS;
|
||||
rem = ((long)lcltime) % SECSPERDAY;
|
||||
if (rem < 0)
|
||||
{
|
||||
|
|
@ -71,65 +75,25 @@ _DEFUN (gmtime_r, (tim_p, res),
|
|||
weekday += DAYSPERWEEK;
|
||||
res->tm_wday = weekday;
|
||||
|
||||
/* compute year & day of year */
|
||||
years400 = days / DAYS_PER_400_YEARS;
|
||||
days -= years400 * DAYS_PER_400_YEARS;
|
||||
/* simplify by making the values positive */
|
||||
if (days < 0)
|
||||
{
|
||||
days += DAYS_PER_400_YEARS;
|
||||
--years400;
|
||||
}
|
||||
/* compute year, month, day & day of year */
|
||||
/* for description of this algorithm see
|
||||
* http://howardhinnant.github.io/date_algorithms.html#civil_from_days */
|
||||
era = (days >= 0 ? days : days - (DAYS_PER_ERA - 1)) / DAYS_PER_ERA;
|
||||
eraday = days - era * DAYS_PER_ERA; /* [0, 146096] */
|
||||
erayear = (eraday - eraday / (DAYS_PER_4_YEARS - 1) + eraday / DAYS_PER_CENTURY -
|
||||
eraday / (DAYS_PER_ERA - 1)) / 365; /* [0, 399] */
|
||||
yearday = eraday - (DAYS_PER_YEAR * erayear + erayear / 4 - erayear / 100); /* [0, 365] */
|
||||
month = (5 * yearday + 2) / 153; /* [0, 11] */
|
||||
day = yearday - (153 * month + 2) / 5 + 1; /* [1, 31] */
|
||||
month += month < 10 ? 2 : -10;
|
||||
year = ADJUSTED_EPOCH_YEAR + erayear + era * YEARS_PER_ERA + (month <= 1);
|
||||
|
||||
years100 = days / DAYS_PER_100_YEARS;
|
||||
if (years100 == 4) /* required for proper day of year calculation */
|
||||
--years100;
|
||||
days -= years100 * DAYS_PER_100_YEARS;
|
||||
years4 = days / DAYS_PER_4_YEARS;
|
||||
days -= years4 * DAYS_PER_4_YEARS;
|
||||
remainingyears = days / DAYS_PER_YEAR;
|
||||
if (remainingyears == 4) /* required for proper day of year calculation */
|
||||
--remainingyears;
|
||||
days -= remainingyears * DAYS_PER_YEAR;
|
||||
|
||||
year = ADJUSTED_EPOCH_YEAR + years400 * 400 + years100 * 100 + years4 * 4 +
|
||||
remainingyears;
|
||||
|
||||
/* If remainingyears is zero, it means that the years were completely
|
||||
* "consumed" by modulo calculations by 400, 100 and 4, so the year is:
|
||||
* 1. a multiple of 4, but not a multiple of 100 or 400 - it's a leap year,
|
||||
* 2. a multiple of 4 and 100, but not a multiple of 400 - it's not a leap
|
||||
* year,
|
||||
* 3. a multiple of 4, 100 and 400 - it's a leap year.
|
||||
* If years4 is non-zero, it means that the year is not a multiple of 100 or
|
||||
* 400 (case 1), so it's a leap year. If years100 is zero (and years4 is zero
|
||||
* - due to short-circuiting), it means that the year is a multiple of 400
|
||||
* (case 3), so it's also a leap year. */
|
||||
yearleap = remainingyears == 0 && (years4 != 0 || years100 == 0);
|
||||
|
||||
/* adjust back to 1st January */
|
||||
yearday = days + DAYS_IN_JANUARY + DAYS_IN_FEBRUARY + yearleap;
|
||||
if (yearday >= DAYS_PER_YEAR + yearleap)
|
||||
{
|
||||
yearday -= DAYS_PER_YEAR + yearleap;
|
||||
++year;
|
||||
}
|
||||
res->tm_yday = yearday;
|
||||
res->tm_yday = yearday >= DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY ?
|
||||
yearday - (DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY) :
|
||||
yearday + DAYS_IN_JANUARY + DAYS_IN_FEBRUARY + isleap(erayear);
|
||||
res->tm_year = year - YEAR_BASE;
|
||||
|
||||
/* Because "days" is the number of days since 1st March, the additional leap
|
||||
* day (29th of February) is the last possible day, so it doesn't matter much
|
||||
* whether the year is actually leap or not. */
|
||||
ip = __month_lengths[1];
|
||||
month = 2;
|
||||
while (days >= ip[month])
|
||||
{
|
||||
days -= ip[month];
|
||||
if (++month >= MONSPERYEAR)
|
||||
month = 0;
|
||||
}
|
||||
res->tm_mon = month;
|
||||
res->tm_mday = days + 1;
|
||||
res->tm_mday = day;
|
||||
|
||||
res->tm_isdst = 0;
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue