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Make PRMJ_basetime faster by making it close to O(1) in the year instead of

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O(N).  Bug 360484, r=shaver
This commit is contained in:
bzbarsky%mit.edu 2006-11-13 21:33:06 +00:00
parent 5a8b3013c7
commit 701b361f78
1 changed files with 72 additions and 23 deletions
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95
js/src/prmjtime.c
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@ -72,15 +72,15 @@ extern int gettimeofday(struct timeval *tv);
#endif /* XP_UNIX */
#define IS_LEAP(year) \
(year != 0 && ((((year & 0x3) == 0) && \
((year - ((year/100) * 100)) != 0)) || \
(year - ((year/400) * 400)) == 0))
#define PRMJ_YEAR_DAYS 365L
#define PRMJ_FOUR_YEARS_DAYS (4 * PRMJ_YEAR_DAYS + 1)
#define PRMJ_CENTURY_DAYS (25 * PRMJ_FOUR_YEARS_DAYS - 1)
#define PRMJ_FOUR_CENTURIES_DAYS (4 * PRMJ_CENTURY_DAYS + 1)
#define PRMJ_HOUR_SECONDS 3600L
#define PRMJ_DAY_SECONDS (24L * PRMJ_HOUR_SECONDS)
#define PRMJ_YEAR_SECONDS (PRMJ_DAY_SECONDS * 365L)
#define PRMJ_YEAR_SECONDS (PRMJ_DAY_SECONDS * PRMJ_YEAR_DAYS)
#define PRMJ_MAX_UNIX_TIMET 2145859200L /*time_t value equiv. to 12/31/2037 */
/* function prototypes */
static void PRMJ_basetime(JSInt64 tsecs, PRMJTime *prtm);
/*
@ -351,9 +351,29 @@ PRMJ_basetime(JSInt64 tsecs, PRMJTime *prtm)
JSInt64 result2;
JSInt64 base;
/* Some variables for intermediate result storage to make computing isleap
easier/faster */
JSInt32 fourCenturyBlocks;
JSInt32 centuriesLeft;
JSInt32 fourYearBlocksLeft;
JSInt32 yearsLeft;
/* Since leap years work by 400/100/4 year intervals, precompute the length
of those in seconds if they start at the beginning of year 1. */
JSInt64 fourYears;
JSInt64 century;
JSInt64 fourCenturies;
JSLL_I2L(fourYears, PRMJ_FOUR_YEARS_DAYS);
JSLL_MUL(fourYears, fourYears, PRMJ_DAY_SECONDS);
JSLL_I2L(century, PRMJ_CENTURY_DAYS);
JSLL_MUL(century, century, PRMJ_DAY_SECONDS);
JSLL_I2L(fourCenturies, PRMJ_FOUR_CENTURIES_DAYS);
JSLL_MUL(fourCenturies, fourCenturies, PRMJ_DAY_SECONDS);
JSLL_UI2L(result,0);
JSLL_UI2L(result1,0);
JSLL_UI2L(result2,0);
/* get the base time via UTC */
base = PRMJ_ToExtendedTime(0);
@ -361,24 +381,53 @@ PRMJ_basetime(JSInt64 tsecs, PRMJTime *prtm)
JSLL_DIV(base,base,result);
JSLL_ADD(tsecs,tsecs,base);
JSLL_UI2L(result, PRMJ_YEAR_SECONDS);
JSLL_UI2L(result1,PRMJ_DAY_SECONDS);
JSLL_ADD(result2,result,result1);
/* Compute our |year|, |isleap|, and part of |days|. When this part is
done, |year| should hold the year our date falls in (number of whole
years elapsed before our date), isleap should hold 1 if the year the
date falls in is a leap year and 0 otherwise. */
/* get the year */
while ((isleap == 0) ? !JSLL_CMP(tsecs,<,result) : !JSLL_CMP(tsecs,<,result2)) {
/* subtract a year from tsecs */
JSLL_SUB(tsecs,tsecs,result);
days += 365;
/* is it a leap year ? */
if(IS_LEAP(year)){
JSLL_SUB(tsecs,tsecs,result1);
days++;
}
year++;
isleap = IS_LEAP(year);
/* First do year 0; it's special and nonleap. */
JSLL_UI2L(result, PRMJ_YEAR_SECONDS);
if (!JSLL_CMP(tsecs,<,result)) {
days = PRMJ_YEAR_DAYS;
year = 1;
JSLL_SUB(tsecs, tsecs, result);
}
/* Now use those constants we computed above */
JSLL_UDIVMOD(&result1, &result2, tsecs, fourCenturies);
JSLL_L2I(fourCenturyBlocks, result1);
year += fourCenturyBlocks * 400;
days += fourCenturyBlocks * PRMJ_FOUR_CENTURIES_DAYS;
tsecs = result2;
JSLL_UDIVMOD(&result1, &result2, tsecs, century);
JSLL_L2I(centuriesLeft, result1);
year += centuriesLeft * 100;
days += centuriesLeft * PRMJ_CENTURY_DAYS;
tsecs = result2;
JSLL_UDIVMOD(&result1, &result2, tsecs, fourYears);
JSLL_L2I(fourYearBlocksLeft, result1);
year += fourYearBlocksLeft * 4;
days += fourYearBlocksLeft * PRMJ_FOUR_YEARS_DAYS;
tsecs = result2;
/* Recall that |result| holds PRMJ_YEAR_SECONDS */
JSLL_UDIVMOD(&result1, &result2, tsecs, result);
JSLL_L2I(yearsLeft, result1);
year += yearsLeft;
days += yearsLeft * PRMJ_YEAR_DAYS;
tsecs = result2;
/* now compute isleap. Note that we don't have to use %, since we've
already computed those remainders. Also note that they're all offset by
1 because of the 1 for year 0. */
isleap =
(yearsLeft == 3) && (fourYearBlocksLeft != 24 || centuriesLeft == 3);
JS_ASSERT(isleap ==
((year % 4 == 0) && (year % 100 != 0 || year % 400 == 0)));
JSLL_UI2L(result1,PRMJ_DAY_SECONDS);
JSLL_DIV(result,tsecs,result1);