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gmtime_r: Use faster algorithm by Howard Hinnant

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* 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
2015-06-15 12:00:59 +02:00
committed by Corinna Vinschen
parent b81a830f1a
commit 325926031b
2 changed files with 40 additions and 71 deletions
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5
newlib/ChangeLog
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@@ -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

106
newlib/libc/time/gmtime_r.c
View File

@@ -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;