/* * ntp_calendar.c - calendar and helper functions * * Written by Juergen Perlinger (perlinger@ntp.org) for the NTP project. * The contents of 'html/copyright.html' apply. * * -------------------------------------------------------------------- * Some notes on the implementation: * * Calendar algorithms thrive on the division operation, which is one of * the slowest numerical operations in any CPU. What saves us here from * abysmal performance is the fact that all divisions are divisions by * constant numbers, and most compilers can do this by a multiplication * operation. But this might not work when using the div/ldiv/lldiv * function family, because many compilers are not able to do inline * expansion of the code with following optimisation for the * constant-divider case. * * Also div/ldiv/lldiv are defined in terms of int/long/longlong, which * are inherently target dependent. Nothing that could not be cured with * autoconf, but still a mess... * * Furthermore, we need floor division in many places. C either leaves * the division behaviour undefined (< C99) or demands truncation to * zero (>= C99), so additional steps are required to make sure the * algorithms work. The {l,ll}div function family is requested to * truncate towards zero, which is also the wrong direction for our * purpose. * * For all this, all divisions by constant are coded manually, even when * there is a joined div/mod operation: The optimiser should sort that * out, if possible. Most of the calculations are done with unsigned * types, explicitely using two's complement arithmetics where * necessary. This minimises the dependecies to compiler and target, * while still giving reasonable to good performance. * * The implementation uses a few tricks that exploit properties of the * two's complement: Floor division on negative dividents can be * executed by using the one's complement of the divident. One's * complement can be easily created using XOR and a mask. * * Finally, check for overflow conditions is minimal. There are only two * calculation steps in the whole calendar that suffer from an internal * overflow, and these conditions are checked: errno is set to EDOM and * the results are clamped/saturated in this case. All other functions * do not suffer from internal overflow and simply return the result * truncated to 32 bits. * * This is a sacrifice made for execution speed. Since a 32-bit day * counter covers +/- 5,879,610 years and the clamp limits the effective * range to +/-2.9 million years, this should not pose a problem here. * */ #include #include #include "ntp_types.h" #include "ntp_calendar.h" #include "ntp_stdlib.h" #include "ntp_fp.h" #include "ntp_unixtime.h" /* For now, let's take the conservative approach: if the target property * macros are not defined, check a few well-known compiler/architecture * settings. Default is to assume that the representation of signed * integers is unknown and shift-arithmetic-right is not available. */ #ifndef TARGET_HAS_2CPL # if defined(__GNUC__) # if defined(__i386__) || defined(__x86_64__) || defined(__arm__) # define TARGET_HAS_2CPL 1 # else # define TARGET_HAS_2CPL 0 # endif # elif defined(_MSC_VER) # if defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM) # define TARGET_HAS_2CPL 1 # else # define TARGET_HAS_2CPL 0 # endif # else # define TARGET_HAS_2CPL 0 # endif #endif #ifndef TARGET_HAS_SAR # define TARGET_HAS_SAR 0 #endif /* *--------------------------------------------------------------------- * replacing the 'time()' function *--------------------------------------------------------------------- */ static systime_func_ptr systime_func = &time; static inline time_t now(void); systime_func_ptr ntpcal_set_timefunc( systime_func_ptr nfunc ) { systime_func_ptr res; res = systime_func; if (NULL == nfunc) nfunc = &time; systime_func = nfunc; return res; } static inline time_t now(void) { return (*systime_func)(NULL); } /* *--------------------------------------------------------------------- * Get sign extension mask and unsigned 2cpl rep for a signed integer *--------------------------------------------------------------------- */ static inline uint32_t int32_sflag( const int32_t v) { # if TARGET_HAS_2CPL && TARGET_HAS_SAR && SIZEOF_INT >= 4 /* Let's assume that shift is the fastest way to get the sign * extension of of a signed integer. This might not always be * true, though -- On 8bit CPUs or machines without barrel * shifter this will kill the performance. So we make sure * we do this only if 'int' has at least 4 bytes. */ return (uint32_t)(v >> 31); # else /* This should be a rather generic approach for getting a sign * extension mask... */ return UINT32_C(0) - (uint32_t)(v < 0); # endif } static inline uint32_t int32_to_uint32_2cpl( const int32_t v) { uint32_t vu; # if TARGET_HAS_2CPL /* Just copy through the 32 bits from the signed value if we're * on a two's complement target. */ vu = (uint32_t)v; # else /* Convert from signed int to unsigned int two's complement. Do * not make any assumptions about the representation of signed * integers, but make sure signed integer overflow cannot happen * here. A compiler on a two's complement target *might* find * out that this is just a complicated cast (as above), but your * mileage might vary. */ if (v < 0) vu = ~(uint32_t)(-(v + 1)); else vu = (uint32_t)v; # endif return vu; } static inline int32_t uint32_2cpl_to_int32( const uint32_t vu) { int32_t v; # if TARGET_HAS_2CPL /* Just copy through the 32 bits from the unsigned value if * we're on a two's complement target. */ v = (int32_t)vu; # else /* Convert to signed integer, making sure signed integer * overflow cannot happen. Again, the optimiser might or might * not find out that this is just a copy of 32 bits on a target * with two's complement representation for signed integers. */ if (vu > INT32_MAX) v = -(int32_t)(~vu) - 1; else v = (int32_t)vu; # endif return v; } /* Some of the calculations need to multiply the input by 4 before doing * a division. This can cause overflow and strange results. Therefore we * clamp / saturate the input operand. And since we do the calculations * in unsigned int with an extra sign flag/mask, we only loose one bit * of the input value range. */ static inline uint32_t uint32_saturate( uint32_t vu, uint32_t mu) { static const uint32_t limit = UINT32_MAX/4u; if ((mu ^ vu) > limit) { vu = mu ^ limit; errno = EDOM; } return vu; } /* *--------------------------------------------------------------------- * Convert between 'time_t' and 'vint64' *--------------------------------------------------------------------- */ vint64 time_to_vint64( const time_t * ptt ) { vint64 res; time_t tt; tt = *ptt; # if SIZEOF_TIME_T <= 4 res.D_s.hi = 0; if (tt < 0) { res.D_s.lo = (uint32_t)-tt; M_NEG(res.D_s.hi, res.D_s.lo); } else { res.D_s.lo = (uint32_t)tt; } # elif defined(HAVE_INT64) res.q_s = tt; # else /* * shifting negative signed quantities is compiler-dependent, so * we better avoid it and do it all manually. And shifting more * than the width of a quantity is undefined. Also a don't do! */ if (tt < 0) { tt = -tt; res.D_s.lo = (uint32_t)tt; res.D_s.hi = (uint32_t)(tt >> 32); M_NEG(res.D_s.hi, res.D_s.lo); } else { res.D_s.lo = (uint32_t)tt; res.D_s.hi = (uint32_t)(tt >> 32); } # endif return res; } time_t vint64_to_time( const vint64 *tv ) { time_t res; # if SIZEOF_TIME_T <= 4 res = (time_t)tv->D_s.lo; # elif defined(HAVE_INT64) res = (time_t)tv->q_s; # else res = ((time_t)tv->d_s.hi << 32) | tv->D_s.lo; # endif return res; } /* *--------------------------------------------------------------------- * Get the build date & time *--------------------------------------------------------------------- */ int ntpcal_get_build_date( struct calendar * jd ) { /* The C standard tells us the format of '__DATE__': * * __DATE__ The date of translation of the preprocessing * translation unit: a character string literal of the form "Mmm * dd yyyy", where the names of the months are the same as those * generated by the asctime function, and the first character of * dd is a space character if the value is less than 10. If the * date of translation is not available, an * implementation-defined valid date shall be supplied. * * __TIME__ The time of translation of the preprocessing * translation unit: a character string literal of the form * "hh:mm:ss" as in the time generated by the asctime * function. If the time of translation is not available, an * implementation-defined valid time shall be supplied. * * Note that MSVC declares DATE and TIME to be in the local time * zone, while neither the C standard nor the GCC docs make any * statement about this. As a result, we may be +/-12hrs off * UTC. But for practical purposes, this should not be a * problem. * */ # ifdef MKREPRO_DATE static const char build[] = MKREPRO_TIME "/" MKREPRO_DATE; # else static const char build[] = __TIME__ "/" __DATE__; # endif static const char mlist[] = "JanFebMarAprMayJunJulAugSepOctNovDec"; char monstr[4]; const char * cp; unsigned short hour, minute, second, day, year; /* Note: The above quantities are used for sscanf 'hu' format, * so using 'uint16_t' is contra-indicated! */ # ifdef DEBUG static int ignore = 0; # endif ZERO(*jd); jd->year = 1970; jd->month = 1; jd->monthday = 1; # ifdef DEBUG /* check environment if build date should be ignored */ if (0 == ignore) { const char * envstr; envstr = getenv("NTPD_IGNORE_BUILD_DATE"); ignore = 1 + (envstr && (!*envstr || !strcasecmp(envstr, "yes"))); } if (ignore > 1) return FALSE; # endif if (6 == sscanf(build, "%hu:%hu:%hu/%3s %hu %hu", &hour, &minute, &second, monstr, &day, &year)) { cp = strstr(mlist, monstr); if (NULL != cp) { jd->year = year; jd->month = (uint8_t)((cp - mlist) / 3 + 1); jd->monthday = (uint8_t)day; jd->hour = (uint8_t)hour; jd->minute = (uint8_t)minute; jd->second = (uint8_t)second; return TRUE; } } return FALSE; } /* *--------------------------------------------------------------------- * basic calendar stuff *--------------------------------------------------------------------- */ /* month table for a year starting with March,1st */ static const uint16_t shift_month_table[13] = { 0, 31, 61, 92, 122, 153, 184, 214, 245, 275, 306, 337, 366 }; /* month tables for years starting with January,1st; regular & leap */ static const uint16_t real_month_table[2][13] = { /* -*- table for regular years -*- */ { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 }, /* -*- table for leap years -*- */ { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 } }; /* * Some notes on the terminology: * * We use the proleptic Gregorian calendar, which is the Gregorian * calendar extended in both directions ad infinitum. This totally * disregards the fact that this calendar was invented in 1582, and * was adopted at various dates over the world; sometimes even after * the start of the NTP epoch. * * Normally date parts are given as current cycles, while time parts * are given as elapsed cycles: * * 1970-01-01/03:04:05 means 'IN the 1970st. year, IN the first month, * ON the first day, with 3hrs, 4minutes and 5 seconds elapsed. * * The basic calculations for this calendar implementation deal with * ELAPSED date units, which is the number of full years, full months * and full days before a date: 1970-01-01 would be (1969, 0, 0) in * that notation. * * To ease the numeric computations, month and day values outside the * normal range are acceptable: 2001-03-00 will be treated as the day * before 2001-03-01, 2000-13-32 will give the same result as * 2001-02-01 and so on. * * 'rd' or 'RD' is used as an abbreviation for the latin 'rata die' * (day number). This is the number of days elapsed since 0000-12-31 * in the proleptic Gregorian calendar. The begin of the Christian Era * (0001-01-01) is RD(1). */ /* * ==================================================================== * * General algorithmic stuff * * ==================================================================== */ /* *--------------------------------------------------------------------- * Do a periodic extension of 'value' around 'pivot' with a period of * 'cycle'. * * The result 'res' is a number that holds to the following properties: * * 1) res MOD cycle == value MOD cycle * 2) pivot <= res < pivot + cycle * (replace />= for negative cycles) * * where 'MOD' denotes the modulo operator for FLOOR DIVISION, which * is not the same as the '%' operator in C: C requires division to be * a truncated division, where remainder and dividend have the same * sign if the remainder is not zero, whereas floor division requires * divider and modulus to have the same sign for a non-zero modulus. * * This function has some useful applications: * * + let Y be a calendar year and V a truncated 2-digit year: then * periodic_extend(Y-50, V, 100) * is the closest expansion of the truncated year with respect to * the full year, that is a 4-digit year with a difference of less * than 50 years to the year Y. ("century unfolding") * * + let T be a UN*X time stamp and V be seconds-of-day: then * perodic_extend(T-43200, V, 86400) * is a time stamp that has the same seconds-of-day as the input * value, with an absolute difference to T of <= 12hrs. ("day * unfolding") * * + Wherever you have a truncated periodic value and a non-truncated * base value and you want to match them somehow... * * Basically, the function delivers 'pivot + (value - pivot) % cycle', * but the implementation takes some pains to avoid internal signed * integer overflows in the '(value - pivot) % cycle' part and adheres * to the floor division convention. * * If 64bit scalars where available on all intended platforms, writing a * version that uses 64 bit ops would be easy; writing a general * division routine for 64bit ops on a platform that can only do * 32/16bit divisions and is still performant is a bit more * difficult. Since most usecases can be coded in a way that does only * require the 32-bit version a 64bit version is NOT provided here. *--------------------------------------------------------------------- */ int32_t ntpcal_periodic_extend( int32_t pivot, int32_t value, int32_t cycle ) { uint32_t diff; char cpl = 0; /* modulo complement flag */ char neg = 0; /* sign change flag */ /* make the cycle positive and adjust the flags */ if (cycle < 0) { cycle = - cycle; neg ^= 1; cpl ^= 1; } /* guard against div by zero or one */ if (cycle > 1) { /* * Get absolute difference as unsigned quantity and * the complement flag. This is done by always * subtracting the smaller value from the bigger * one. */ if (value >= pivot) { diff = int32_to_uint32_2cpl(value) - int32_to_uint32_2cpl(pivot); } else { diff = int32_to_uint32_2cpl(pivot) - int32_to_uint32_2cpl(value); cpl ^= 1; } diff %= (uint32_t)cycle; if (diff) { if (cpl) diff = (uint32_t)cycle - diff; if (neg) diff = ~diff + 1; pivot += uint32_2cpl_to_int32(diff); } } return pivot; } /*--------------------------------------------------------------------- * Note to the casual reader * * In the next two functions you will find (or would have found...) * the expression * * res.Q_s -= 0x80000000; * * There was some ruckus about a possible programming error due to * integer overflow and sign propagation. * * This assumption is based on a lack of understanding of the C * standard. (Though this is admittedly not one of the most 'natural' * aspects of the 'C' language and easily to get wrong.) * * see * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf * "ISO/IEC 9899:201x Committee Draft — April 12, 2011" * 6.4.4.1 Integer constants, clause 5 * * why there is no sign extension/overflow problem here. * * But to ease the minds of the doubtful, I added back the 'u' qualifiers * that somehow got lost over the last years. */ /* *--------------------------------------------------------------------- * Convert a timestamp in NTP scale to a 64bit seconds value in the UN*X * scale with proper epoch unfolding around a given pivot or the current * system time. This function happily accepts negative pivot values as * timestamps befor 1970-01-01, so be aware of possible trouble on * platforms with 32bit 'time_t'! * * This is also a periodic extension, but since the cycle is 2^32 and * the shift is 2^31, we can do some *very* fast math without explicit * divisions. *--------------------------------------------------------------------- */ vint64 ntpcal_ntp_to_time( uint32_t ntp, const time_t * pivot ) { vint64 res; # if defined(HAVE_INT64) res.q_s = (pivot != NULL) ? *pivot : now(); res.Q_s -= 0x80000000u; /* unshift of half range */ ntp -= (uint32_t)JAN_1970; /* warp into UN*X domain */ ntp -= res.D_s.lo; /* cycle difference */ res.Q_s += (uint64_t)ntp; /* get expanded time */ # else /* no 64bit scalars */ time_t tmp; tmp = (pivot != NULL) ? *pivot : now(); res = time_to_vint64(&tmp); M_SUB(res.D_s.hi, res.D_s.lo, 0, 0x80000000u); ntp -= (uint32_t)JAN_1970; /* warp into UN*X domain */ ntp -= res.D_s.lo; /* cycle difference */ M_ADD(res.D_s.hi, res.D_s.lo, 0, ntp); # endif /* no 64bit scalars */ return res; } /* *--------------------------------------------------------------------- * Convert a timestamp in NTP scale to a 64bit seconds value in the NTP * scale with proper epoch unfolding around a given pivot or the current * system time. * * Note: The pivot must be given in the UN*X time domain! * * This is also a periodic extension, but since the cycle is 2^32 and * the shift is 2^31, we can do some *very* fast math without explicit * divisions. *--------------------------------------------------------------------- */ vint64 ntpcal_ntp_to_ntp( uint32_t ntp, const time_t *pivot ) { vint64 res; # if defined(HAVE_INT64) res.q_s = (pivot) ? *pivot : now(); res.Q_s -= 0x80000000u; /* unshift of half range */ res.Q_s += (uint32_t)JAN_1970; /* warp into NTP domain */ ntp -= res.D_s.lo; /* cycle difference */ res.Q_s += (uint64_t)ntp; /* get expanded time */ # else /* no 64bit scalars */ time_t tmp; tmp = (pivot) ? *pivot : now(); res = time_to_vint64(&tmp); M_SUB(res.D_s.hi, res.D_s.lo, 0, 0x80000000u); M_ADD(res.D_s.hi, res.D_s.lo, 0, (uint32_t)JAN_1970);/*into NTP */ ntp -= res.D_s.lo; /* cycle difference */ M_ADD(res.D_s.hi, res.D_s.lo, 0, ntp); # endif /* no 64bit scalars */ return res; } /* * ==================================================================== * * Splitting values to composite entities * * ==================================================================== */ /* *--------------------------------------------------------------------- * Split a 64bit seconds value into elapsed days in 'res.hi' and * elapsed seconds since midnight in 'res.lo' using explicit floor * division. This function happily accepts negative time values as * timestamps before the respective epoch start. *--------------------------------------------------------------------- */ ntpcal_split ntpcal_daysplit( const vint64 *ts ) { ntpcal_split res; uint32_t Q; # if defined(HAVE_INT64) /* Manual floor division by SECSPERDAY. This uses the one's * complement trick, too, but without an extra flag value: The * flag would be 64bit, and that's a bit of overkill on a 32bit * target that has to use a register pair for a 64bit number. */ if (ts->q_s < 0) Q = ~(uint32_t)(~ts->Q_s / SECSPERDAY); else Q = (uint32_t)(ts->Q_s / SECSPERDAY); # else uint32_t ah, al, sflag, A; /* get operand into ah/al (either ts or ts' one's complement, * for later floor division) */ sflag = int32_sflag(ts->d_s.hi); ah = sflag ^ ts->D_s.hi; al = sflag ^ ts->D_s.lo; /* Since 86400 == 128*675 we can drop the least 7 bits and * divide by 675 instead of 86400. Then the maximum remainder * after each devision step is 674, and we need 10 bits for * that. So in the next step we can shift in 22 bits from the * numerator. * * Therefore we load the accu with the top 13 bits (51..63) in * the first shot. We don't have to remember the quotient -- it * would be shifted out anyway. */ A = ah >> 19; if (A >= 675) A = (A % 675u); /* Now assemble the remainder with bits 29..50 from the * numerator and divide. This creates the upper ten bits of the * quotient. (Well, the top 22 bits of a 44bit result. But that * will be truncated to 32 bits anyway.) */ A = (A << 19) | (ah & 0x0007FFFFu); A = (A << 3) | (al >> 29); Q = A / 675u; A = A % 675u; /* Now assemble the remainder with bits 7..28 from the numerator * and do a final division step. */ A = (A << 22) | ((al >> 7) & 0x003FFFFFu); Q = (Q << 22) | (A / 675u); /* The last 7 bits get simply dropped, as they have no affect on * the quotient when dividing by 86400. */ /* apply sign correction and calculate the true floor * remainder. */ Q ^= sflag; # endif res.hi = uint32_2cpl_to_int32(Q); res.lo = ts->D_s.lo - Q * SECSPERDAY; return res; } /* *--------------------------------------------------------------------- * Split a 32bit seconds value into h/m/s and excessive days. This * function happily accepts negative time values as timestamps before * midnight. *--------------------------------------------------------------------- */ static int32_t priv_timesplit( int32_t split[3], int32_t ts ) { /* Do 3 chained floor divisions by positive constants, using the * one's complement trick and factoring out the intermediate XOR * ops to reduce the number of operations. */ uint32_t us, um, uh, ud, sflag; sflag = int32_sflag(ts); us = int32_to_uint32_2cpl(ts); um = (sflag ^ us) / SECSPERMIN; uh = um / MINSPERHR; ud = uh / HRSPERDAY; um ^= sflag; uh ^= sflag; ud ^= sflag; split[0] = (int32_t)(uh - ud * HRSPERDAY ); split[1] = (int32_t)(um - uh * MINSPERHR ); split[2] = (int32_t)(us - um * SECSPERMIN); return uint32_2cpl_to_int32(ud); } /* *--------------------------------------------------------------------- * Given the number of elapsed days in the calendar era, split this * number into the number of elapsed years in 'res.hi' and the number * of elapsed days of that year in 'res.lo'. * * if 'isleapyear' is not NULL, it will receive an integer that is 0 for * regular years and a non-zero value for leap years. *--------------------------------------------------------------------- */ ntpcal_split ntpcal_split_eradays( int32_t days, int *isleapyear ) { /* Use the fast cyclesplit algorithm here, to calculate the * centuries and years in a century with one division each. This * reduces the number of division operations to two, but is * susceptible to internal range overflow. We make sure the * input operands are in the safe range; this still gives us * approx +/-2.9 million years. */ ntpcal_split res; int32_t n100, n001; /* calendar year cycles */ uint32_t uday, Q, sflag; /* split off centuries first */ sflag = int32_sflag(days); uday = uint32_saturate(int32_to_uint32_2cpl(days), sflag); uday = (4u * uday) | 3u; Q = sflag ^ ((sflag ^ uday) / GREGORIAN_CYCLE_DAYS); uday = uday - Q * GREGORIAN_CYCLE_DAYS; n100 = uint32_2cpl_to_int32(Q); /* Split off years in century -- days >= 0 here, and we're far * away from integer overflow trouble now. */ uday |= 3; n001 = uday / GREGORIAN_NORMAL_LEAP_CYCLE_DAYS; uday = uday % GREGORIAN_NORMAL_LEAP_CYCLE_DAYS; /* Assemble the year and day in year */ res.hi = n100 * 100 + n001; res.lo = uday / 4u; /* Eventually set the leap year flag. Note: 0 <= n001 <= 99 and * Q is still the two's complement representation of the * centuries: The modulo 4 ops can be done with masking here. * We also shift the year and the century by one, so the tests * can be done against zero instead of 3. */ if (isleapyear) *isleapyear = !((n001+1) & 3) && ((n001 != 99) || !((Q+1) & 3)); return res; } /* *--------------------------------------------------------------------- * Given a number of elapsed days in a year and a leap year indicator, * split the number of elapsed days into the number of elapsed months in * 'res.hi' and the number of elapsed days of that month in 'res.lo'. * * This function will fail and return {-1,-1} if the number of elapsed * days is not in the valid range! *--------------------------------------------------------------------- */ ntpcal_split ntpcal_split_yeardays( int32_t eyd, int isleapyear ) { ntpcal_split res; const uint16_t *lt; /* month length table */ /* check leap year flag and select proper table */ lt = real_month_table[(isleapyear != 0)]; if (0 <= eyd && eyd < lt[12]) { /* get zero-based month by approximation & correction step */ res.hi = eyd >> 5; /* approx month; might be 1 too low */ if (lt[res.hi + 1] <= eyd) /* fixup approximative month value */ res.hi += 1; res.lo = eyd - lt[res.hi]; } else { res.lo = res.hi = -1; } return res; } /* *--------------------------------------------------------------------- * Convert a RD into the date part of a 'struct calendar'. *--------------------------------------------------------------------- */ int ntpcal_rd_to_date( struct calendar *jd, int32_t rd ) { ntpcal_split split; int leapy; u_int ymask; /* Get day-of-week first. Since rd is signed, the remainder can * be in the range [-6..+6], but the assignment to an unsigned * variable maps the negative values to positive values >=7. * This makes the sign correction look strange, but adding 7 * causes the needed wrap-around into the desired value range of * zero to six, both inclusive. */ jd->weekday = rd % DAYSPERWEEK; if (jd->weekday >= DAYSPERWEEK) /* weekday is unsigned! */ jd->weekday += DAYSPERWEEK; split = ntpcal_split_eradays(rd - 1, &leapy); /* Get year and day-of-year, with overflow check. If any of the * upper 16 bits is set after shifting to unity-based years, we * will have an overflow when converting to an unsigned 16bit * year. Shifting to the right is OK here, since it does not * matter if the shift is logic or arithmetic. */ split.hi += 1; ymask = 0u - ((split.hi >> 16) == 0); jd->year = (uint16_t)(split.hi & ymask); jd->yearday = (uint16_t)split.lo + 1; /* convert to month and mday */ split = ntpcal_split_yeardays(split.lo, leapy); jd->month = (uint8_t)split.hi + 1; jd->monthday = (uint8_t)split.lo + 1; return ymask ? leapy : -1; } /* *--------------------------------------------------------------------- * Convert a RD into the date part of a 'struct tm'. *--------------------------------------------------------------------- */ int ntpcal_rd_to_tm( struct tm *utm, int32_t rd ) { ntpcal_split split; int leapy; /* get day-of-week first */ utm->tm_wday = rd % DAYSPERWEEK; if (utm->tm_wday < 0) utm->tm_wday += DAYSPERWEEK; /* get year and day-of-year */ split = ntpcal_split_eradays(rd - 1, &leapy); utm->tm_year = split.hi - 1899; utm->tm_yday = split.lo; /* 0-based */ /* convert to month and mday */ split = ntpcal_split_yeardays(split.lo, leapy); utm->tm_mon = split.hi; /* 0-based */ utm->tm_mday = split.lo + 1; /* 1-based */ return leapy; } /* *--------------------------------------------------------------------- * Take a value of seconds since midnight and split it into hhmmss in a * 'struct calendar'. *--------------------------------------------------------------------- */ int32_t ntpcal_daysec_to_date( struct calendar *jd, int32_t sec ) { int32_t days; int ts[3]; days = priv_timesplit(ts, sec); jd->hour = (uint8_t)ts[0]; jd->minute = (uint8_t)ts[1]; jd->second = (uint8_t)ts[2]; return days; } /* *--------------------------------------------------------------------- * Take a value of seconds since midnight and split it into hhmmss in a * 'struct tm'. *--------------------------------------------------------------------- */ int32_t ntpcal_daysec_to_tm( struct tm *utm, int32_t sec ) { int32_t days; int32_t ts[3]; days = priv_timesplit(ts, sec); utm->tm_hour = ts[0]; utm->tm_min = ts[1]; utm->tm_sec = ts[2]; return days; } /* *--------------------------------------------------------------------- * take a split representation for day/second-of-day and day offset * and convert it to a 'struct calendar'. The seconds will be normalised * into the range of a day, and the day will be adjusted accordingly. * * returns >0 if the result is in a leap year, 0 if in a regular * year and <0 if the result did not fit into the calendar struct. *--------------------------------------------------------------------- */ int ntpcal_daysplit_to_date( struct calendar *jd, const ntpcal_split *ds, int32_t dof ) { dof += ntpcal_daysec_to_date(jd, ds->lo); return ntpcal_rd_to_date(jd, ds->hi + dof); } /* *--------------------------------------------------------------------- * take a split representation for day/second-of-day and day offset * and convert it to a 'struct tm'. The seconds will be normalised * into the range of a day, and the day will be adjusted accordingly. * * returns 1 if the result is in a leap year and zero if in a regular * year. *--------------------------------------------------------------------- */ int ntpcal_daysplit_to_tm( struct tm *utm, const ntpcal_split *ds , int32_t dof ) { dof += ntpcal_daysec_to_tm(utm, ds->lo); return ntpcal_rd_to_tm(utm, ds->hi + dof); } /* *--------------------------------------------------------------------- * Take a UN*X time and convert to a calendar structure. *--------------------------------------------------------------------- */ int ntpcal_time_to_date( struct calendar *jd, const vint64 *ts ) { ntpcal_split ds; ds = ntpcal_daysplit(ts); ds.hi += ntpcal_daysec_to_date(jd, ds.lo); ds.hi += DAY_UNIX_STARTS; return ntpcal_rd_to_date(jd, ds.hi); } /* * ==================================================================== * * merging composite entities * * ==================================================================== */ /* *--------------------------------------------------------------------- * Merge a number of days and a number of seconds into seconds, * expressed in 64 bits to avoid overflow. *--------------------------------------------------------------------- */ vint64 ntpcal_dayjoin( int32_t days, int32_t secs ) { vint64 res; # if defined(HAVE_INT64) res.q_s = days; res.q_s *= SECSPERDAY; res.q_s += secs; # else uint32_t p1, p2; int isneg; /* * res = days *86400 + secs, using manual 16/32 bit * multiplications and shifts. */ isneg = (days < 0); if (isneg) days = -days; /* assemble days * 675 */ res.D_s.lo = (days & 0xFFFF) * 675u; res.D_s.hi = 0; p1 = (days >> 16) * 675u; p2 = p1 >> 16; p1 = p1 << 16; M_ADD(res.D_s.hi, res.D_s.lo, p2, p1); /* mul by 128, using shift */ res.D_s.hi = (res.D_s.hi << 7) | (res.D_s.lo >> 25); res.D_s.lo = (res.D_s.lo << 7); /* fix sign */ if (isneg) M_NEG(res.D_s.hi, res.D_s.lo); /* properly add seconds */ p2 = 0; if (secs < 0) { p1 = (uint32_t)-secs; M_NEG(p2, p1); } else { p1 = (uint32_t)secs; } M_ADD(res.D_s.hi, res.D_s.lo, p2, p1); # endif return res; } /* *--------------------------------------------------------------------- * get leap years since epoch in elapsed years *--------------------------------------------------------------------- */ int32_t ntpcal_leapyears_in_years( int32_t years ) { /* We use the in-out-in algorithm here, using the one's * complement division trick for negative numbers. The chained * division sequence by 4/25/4 gives the compiler the chance to * get away with only one true division and doing shifts otherwise. */ uint32_t sflag, sum, uyear; sflag = int32_sflag(years); uyear = int32_to_uint32_2cpl(years); uyear ^= sflag; sum = (uyear /= 4u); /* 4yr rule --> IN */ sum -= (uyear /= 25u); /* 100yr rule --> OUT */ sum += (uyear /= 4u); /* 400yr rule --> IN */ /* Thanks to the alternation of IN/OUT/IN we can do the sum * directly and have a single one's complement operation * here. (Only if the years are negative, of course.) Otherwise * the one's complement would have to be done when * adding/subtracting the terms. */ return uint32_2cpl_to_int32(sflag ^ sum); } /* *--------------------------------------------------------------------- * Convert elapsed years in Era into elapsed days in Era. *--------------------------------------------------------------------- */ int32_t ntpcal_days_in_years( int32_t years ) { return years * DAYSPERYEAR + ntpcal_leapyears_in_years(years); } /* *--------------------------------------------------------------------- * Convert a number of elapsed month in a year into elapsed days in year. * * The month will be normalized, and 'res.hi' will contain the * excessive years that must be considered when converting the years, * while 'res.lo' will contain the number of elapsed days since start * of the year. * * This code uses the shifted-month-approach to convert month to days, * because then there is no need to have explicit leap year * information. The slight disadvantage is that for most month values * the result is a negative value, and the year excess is one; the * conversion is then simply based on the start of the following year. *--------------------------------------------------------------------- */ ntpcal_split ntpcal_days_in_months( int32_t m ) { ntpcal_split res; /* Add ten months and correct if needed. (It likely is...) */ res.lo = m + 10; res.hi = (res.lo >= 12); if (res.hi) res.lo -= 12; /* if still out of range, normalise by floor division ... */ if (res.lo < 0 || res.lo >= 12) { uint32_t mu, Q, sflag; sflag = int32_sflag(res.lo); mu = int32_to_uint32_2cpl(res.lo); Q = sflag ^ ((sflag ^ mu) / 12u); res.hi += uint32_2cpl_to_int32(Q); res.lo = mu - Q * 12u; } /* get cummulated days in year with unshift */ res.lo = shift_month_table[res.lo] - 306; return res; } /* *--------------------------------------------------------------------- * Convert ELAPSED years/months/days of gregorian calendar to elapsed * days in Gregorian epoch. * * If you want to convert years and days-of-year, just give a month of * zero. *--------------------------------------------------------------------- */ int32_t ntpcal_edate_to_eradays( int32_t years, int32_t mons, int32_t mdays ) { ntpcal_split tmp; int32_t res; if (mons) { tmp = ntpcal_days_in_months(mons); res = ntpcal_days_in_years(years + tmp.hi) + tmp.lo; } else res = ntpcal_days_in_years(years); res += mdays; return res; } /* *--------------------------------------------------------------------- * Convert ELAPSED years/months/days of gregorian calendar to elapsed * days in year. * * Note: This will give the true difference to the start of the given * year, even if months & days are off-scale. *--------------------------------------------------------------------- */ int32_t ntpcal_edate_to_yeardays( int32_t years, int32_t mons, int32_t mdays ) { ntpcal_split tmp; if (0 <= mons && mons < 12) { years += 1; mdays += real_month_table[is_leapyear(years)][mons]; } else { tmp = ntpcal_days_in_months(mons); mdays += tmp.lo + ntpcal_days_in_years(years + tmp.hi) - ntpcal_days_in_years(years); } return mdays; } /* *--------------------------------------------------------------------- * Convert elapsed days and the hour/minute/second information into * total seconds. * * If 'isvalid' is not NULL, do a range check on the time specification * and tell if the time input is in the normal range, permitting for a * single leapsecond. *--------------------------------------------------------------------- */ int32_t ntpcal_etime_to_seconds( int32_t hours, int32_t minutes, int32_t seconds ) { int32_t res; res = (hours * MINSPERHR + minutes) * SECSPERMIN + seconds; return res; } /* *--------------------------------------------------------------------- * Convert the date part of a 'struct tm' (that is, year, month, * day-of-month) into the RD of that day. *--------------------------------------------------------------------- */ int32_t ntpcal_tm_to_rd( const struct tm *utm ) { return ntpcal_edate_to_eradays(utm->tm_year + 1899, utm->tm_mon, utm->tm_mday - 1) + 1; } /* *--------------------------------------------------------------------- * Convert the date part of a 'struct calendar' (that is, year, month, * day-of-month) into the RD of that day. *--------------------------------------------------------------------- */ int32_t ntpcal_date_to_rd( const struct calendar *jd ) { return ntpcal_edate_to_eradays((int32_t)jd->year - 1, (int32_t)jd->month - 1, (int32_t)jd->monthday - 1) + 1; } /* *--------------------------------------------------------------------- * convert a year number to rata die of year start *--------------------------------------------------------------------- */ int32_t ntpcal_year_to_ystart( int32_t year ) { return ntpcal_days_in_years(year - 1) + 1; } /* *--------------------------------------------------------------------- * For a given RD, get the RD of the associated year start, * that is, the RD of the last January,1st on or before that day. *--------------------------------------------------------------------- */ int32_t ntpcal_rd_to_ystart( int32_t rd ) { /* * Rather simple exercise: split the day number into elapsed * years and elapsed days, then remove the elapsed days from the * input value. Nice'n sweet... */ return rd - ntpcal_split_eradays(rd - 1, NULL).lo; } /* *--------------------------------------------------------------------- * For a given RD, get the RD of the associated month start. *--------------------------------------------------------------------- */ int32_t ntpcal_rd_to_mstart( int32_t rd ) { ntpcal_split split; int leaps; split = ntpcal_split_eradays(rd - 1, &leaps); split = ntpcal_split_yeardays(split.lo, leaps); return rd - split.lo; } /* *--------------------------------------------------------------------- * take a 'struct calendar' and get the seconds-of-day from it. *--------------------------------------------------------------------- */ int32_t ntpcal_date_to_daysec( const struct calendar *jd ) { return ntpcal_etime_to_seconds(jd->hour, jd->minute, jd->second); } /* *--------------------------------------------------------------------- * take a 'struct tm' and get the seconds-of-day from it. *--------------------------------------------------------------------- */ int32_t ntpcal_tm_to_daysec( const struct tm *utm ) { return ntpcal_etime_to_seconds(utm->tm_hour, utm->tm_min, utm->tm_sec); } /* *--------------------------------------------------------------------- * take a 'struct calendar' and convert it to a 'time_t' *--------------------------------------------------------------------- */ time_t ntpcal_date_to_time( const struct calendar *jd ) { vint64 join; int32_t days, secs; days = ntpcal_date_to_rd(jd) - DAY_UNIX_STARTS; secs = ntpcal_date_to_daysec(jd); join = ntpcal_dayjoin(days, secs); return vint64_to_time(&join); } /* * ==================================================================== * * extended and unchecked variants of caljulian/caltontp * * ==================================================================== */ int ntpcal_ntp64_to_date( struct calendar *jd, const vint64 *ntp ) { ntpcal_split ds; ds = ntpcal_daysplit(ntp); ds.hi += ntpcal_daysec_to_date(jd, ds.lo); return ntpcal_rd_to_date(jd, ds.hi + DAY_NTP_STARTS); } int ntpcal_ntp_to_date( struct calendar *jd, uint32_t ntp, const time_t *piv ) { vint64 ntp64; /* * Unfold ntp time around current time into NTP domain. Split * into days and seconds, shift days into CE domain and * process the parts. */ ntp64 = ntpcal_ntp_to_ntp(ntp, piv); return ntpcal_ntp64_to_date(jd, &ntp64); } vint64 ntpcal_date_to_ntp64( const struct calendar *jd ) { /* * Convert date to NTP. Ignore yearday, use d/m/y only. */ return ntpcal_dayjoin(ntpcal_date_to_rd(jd) - DAY_NTP_STARTS, ntpcal_date_to_daysec(jd)); } uint32_t ntpcal_date_to_ntp( const struct calendar *jd ) { /* * Get lower half of 64-bit NTP timestamp from date/time. */ return ntpcal_date_to_ntp64(jd).d_s.lo; } /* * ==================================================================== * * day-of-week calculations * * ==================================================================== */ /* * Given a RataDie and a day-of-week, calculate a RDN that is reater-than, * greater-or equal, closest, less-or-equal or less-than the given RDN * and denotes the given day-of-week */ int32_t ntpcal_weekday_gt( int32_t rdn, int32_t dow ) { return ntpcal_periodic_extend(rdn+1, dow, 7); } int32_t ntpcal_weekday_ge( int32_t rdn, int32_t dow ) { return ntpcal_periodic_extend(rdn, dow, 7); } int32_t ntpcal_weekday_close( int32_t rdn, int32_t dow ) { return ntpcal_periodic_extend(rdn-3, dow, 7); } int32_t ntpcal_weekday_le( int32_t rdn, int32_t dow ) { return ntpcal_periodic_extend(rdn, dow, -7); } int32_t ntpcal_weekday_lt( int32_t rdn, int32_t dow ) { return ntpcal_periodic_extend(rdn-1, dow, -7); } /* * ==================================================================== * * ISO week-calendar conversions * * The ISO8601 calendar defines a calendar of years, weeks and weekdays. * It is related to the Gregorian calendar, and a ISO year starts at the * Monday closest to Jan,1st of the corresponding Gregorian year. A ISO * calendar year has always 52 or 53 weeks, and like the Grogrian * calendar the ISO8601 calendar repeats itself every 400 years, or * 146097 days, or 20871 weeks. * * While it is possible to write ISO calendar functions based on the * Gregorian calendar functions, the following implementation takes a * different approach, based directly on years and weeks. * * Analysis of the tabulated data shows that it is not possible to * interpolate from years to weeks over a full 400 year range; cyclic * shifts over 400 years do not provide a solution here. But it *is* * possible to interpolate over every single century of the 400-year * cycle. (The centennial leap year rule seems to be the culprit here.) * * It can be shown that a conversion from years to weeks can be done * using a linear transformation of the form * * w = floor( y * a + b ) * * where the slope a must hold to * * 52.1780821918 <= a < 52.1791044776 * * and b must be chosen according to the selected slope and the number * of the century in a 400-year period. * * The inverse calculation can also be done in this way. Careful scaling * provides an unlimited set of integer coefficients a,k,b that enable * us to write the calulation in the form * * w = (y * a + b ) / k * y = (w * a' + b') / k' * * In this implementation the values of k and k' are chosen to be * smallest possible powers of two, so the division can be implemented * as shifts if the optimiser chooses to do so. * * ==================================================================== */ /* * Given a number of elapsed (ISO-)years since the begin of the * christian era, return the number of elapsed weeks corresponding to * the number of years. */ int32_t isocal_weeks_in_years( int32_t years ) { /* * use: w = (y * 53431 + b[c]) / 1024 as interpolation */ static const uint16_t bctab[4] = { 157, 449, 597, 889 }; int32_t cs, cw; uint32_t cc, ci, yu, sflag; sflag = int32_sflag(years); yu = int32_to_uint32_2cpl(years); /* split off centuries, using floor division */ cc = sflag ^ ((sflag ^ yu) / 100u); yu -= cc * 100u; /* calculate century cycles shift and cycle index: * Assuming a century is 5217 weeks, we have to add a cycle * shift that is 3 for every 4 centuries, because 3 of the four * centuries have 5218 weeks. So '(cc*3 + 1) / 4' is the actual * correction, and the second century is the defective one. * * Needs floor division by 4, which is done with masking and * shifting. */ ci = cc * 3u + 1; cs = uint32_2cpl_to_int32(sflag ^ ((sflag ^ ci) / 4u)); ci = ci % 4u; /* Get weeks in century. Can use plain division here as all ops * are >= 0, and let the compiler sort out the possible * optimisations. */ cw = (yu * 53431u + bctab[ci]) / 1024u; return uint32_2cpl_to_int32(cc) * 5217 + cs + cw; } /* * Given a number of elapsed weeks since the begin of the christian * era, split this number into the number of elapsed years in res.hi * and the excessive number of weeks in res.lo. (That is, res.lo is * the number of elapsed weeks in the remaining partial year.) */ ntpcal_split isocal_split_eraweeks( int32_t weeks ) { /* * use: y = (w * 157 + b[c]) / 8192 as interpolation */ static const uint16_t bctab[4] = { 85, 130, 17, 62 }; ntpcal_split res; int32_t cc, ci; uint32_t sw, cy, Q, sflag; /* Use two fast cycle-split divisions here. This is again * susceptible to internal overflow, so we check the range. This * still permits more than +/-20 million years, so this is * likely a pure academical problem. * * We want to execute '(weeks * 4 + 2) /% 20871' under floor * division rules in the first step. */ sflag = int32_sflag(weeks); sw = uint32_saturate(int32_to_uint32_2cpl(weeks), sflag); sw = 4u * sw + 2; Q = sflag ^ ((sflag ^ sw) / GREGORIAN_CYCLE_WEEKS); sw -= Q * GREGORIAN_CYCLE_WEEKS; ci = Q % 4u; cc = uint32_2cpl_to_int32(Q); /* Split off years; sw >= 0 here! The scaled weeks in the years * are scaled up by 157 afterwards. */ sw = (sw / 4u) * 157u + bctab[ci]; cy = sw / 8192u; /* ws >> 13 , let the compiler sort it out */ sw = sw % 8192u; /* ws & 8191, let the compiler sort it out */ /* assemble elapsed years and downscale the elapsed weeks in * the year. */ res.hi = 100*cc + cy; res.lo = sw / 157u; return res; } /* * Given a second in the NTP time scale and a pivot, expand the NTP * time stamp around the pivot and convert into an ISO calendar time * stamp. */ int isocal_ntp64_to_date( struct isodate *id, const vint64 *ntp ) { ntpcal_split ds; int32_t ts[3]; uint32_t uw, ud, sflag; /* * Split NTP time into days and seconds, shift days into CE * domain and process the parts. */ ds = ntpcal_daysplit(ntp); /* split time part */ ds.hi += priv_timesplit(ts, ds.lo); id->hour = (uint8_t)ts[0]; id->minute = (uint8_t)ts[1]; id->second = (uint8_t)ts[2]; /* split days into days and weeks, using floor division in unsigned */ ds.hi += DAY_NTP_STARTS - 1; /* shift from NTP to RDN */ sflag = int32_sflag(ds.hi); ud = int32_to_uint32_2cpl(ds.hi); uw = sflag ^ ((sflag ^ ud) / DAYSPERWEEK); ud -= uw * DAYSPERWEEK; ds.hi = uint32_2cpl_to_int32(uw); ds.lo = ud; id->weekday = (uint8_t)ds.lo + 1; /* weekday result */ /* get year and week in year */ ds = isocal_split_eraweeks(ds.hi); /* elapsed years&week*/ id->year = (uint16_t)ds.hi + 1; /* shift to current */ id->week = (uint8_t )ds.lo + 1; return (ds.hi >= 0 && ds.hi < 0x0000FFFF); } int isocal_ntp_to_date( struct isodate *id, uint32_t ntp, const time_t *piv ) { vint64 ntp64; /* * Unfold ntp time around current time into NTP domain, then * convert the full time stamp. */ ntp64 = ntpcal_ntp_to_ntp(ntp, piv); return isocal_ntp64_to_date(id, &ntp64); } /* * Convert a ISO date spec into a second in the NTP time scale, * properly truncated to 32 bit. */ vint64 isocal_date_to_ntp64( const struct isodate *id ) { int32_t weeks, days, secs; weeks = isocal_weeks_in_years((int32_t)id->year - 1) + (int32_t)id->week - 1; days = weeks * 7 + (int32_t)id->weekday; /* days is RDN of ISO date now */ secs = ntpcal_etime_to_seconds(id->hour, id->minute, id->second); return ntpcal_dayjoin(days - DAY_NTP_STARTS, secs); } uint32_t isocal_date_to_ntp( const struct isodate *id ) { /* * Get lower half of 64-bit NTP timestamp from date/time. */ return isocal_date_to_ntp64(id).d_s.lo; } /* * ==================================================================== * 'basedate' support functions * ==================================================================== */ static int32_t s_baseday = NTP_TO_UNIX_DAYS; static int32_t s_gpsweek = 0; int32_t basedate_eval_buildstamp(void) { struct calendar jd; int32_t ed; if (!ntpcal_get_build_date(&jd)) return NTP_TO_UNIX_DAYS; /* The time zone of the build stamp is unspecified; we remove * one day to provide a certain slack. And in case somebody * fiddled with the system clock, we make sure we do not go * before the UNIX epoch (1970-01-01). It's probably not possible * to do this to the clock on most systems, but there are other * ways to tweak the build stamp. */ jd.monthday -= 1; ed = ntpcal_date_to_rd(&jd) - DAY_NTP_STARTS; return (ed < NTP_TO_UNIX_DAYS) ? NTP_TO_UNIX_DAYS : ed; } int32_t basedate_eval_string( const char * str ) { u_short y,m,d; u_long ned; int rc, nc; size_t sl; sl = strlen(str); rc = sscanf(str, "%4hu-%2hu-%2hu%n", &y, &m, &d, &nc); if (rc == 3 && (size_t)nc == sl) { if (m >= 1 && m <= 12 && d >= 1 && d <= 31) return ntpcal_edate_to_eradays(y-1, m-1, d) - DAY_NTP_STARTS; goto buildstamp; } rc = sscanf(str, "%lu%n", &ned, &nc); if (rc == 1 && (size_t)nc == sl) { if (ned <= INT32_MAX) return (int32_t)ned; goto buildstamp; } buildstamp: msyslog(LOG_WARNING, "basedate string \"%s\" invalid, build date substituted!", str); return basedate_eval_buildstamp(); } uint32_t basedate_get_day(void) { return s_baseday; } int32_t basedate_set_day( int32_t day ) { struct calendar jd; int32_t retv; /* set NTP base date for NTP era unfolding */ if (day < NTP_TO_UNIX_DAYS) { msyslog(LOG_WARNING, "baseday_set_day: invalid day (%lu), UNIX epoch substituted", (unsigned long)day); day = NTP_TO_UNIX_DAYS; } retv = s_baseday; s_baseday = day; ntpcal_rd_to_date(&jd, day + DAY_NTP_STARTS); msyslog(LOG_INFO, "basedate set to %04hu-%02hu-%02hu", jd.year, (u_short)jd.month, (u_short)jd.monthday); /* set GPS base week for GPS week unfolding */ day = ntpcal_weekday_ge(day + DAY_NTP_STARTS, CAL_SUNDAY) - DAY_NTP_STARTS; if (day < NTP_TO_GPS_DAYS) day = NTP_TO_GPS_DAYS; s_gpsweek = (day - NTP_TO_GPS_DAYS) / DAYSPERWEEK; ntpcal_rd_to_date(&jd, day + DAY_NTP_STARTS); msyslog(LOG_INFO, "gps base set to %04hu-%02hu-%02hu (week %d)", jd.year, (u_short)jd.month, (u_short)jd.monthday, s_gpsweek); return retv; } time_t basedate_get_eracenter(void) { time_t retv; retv = (time_t)(s_baseday - NTP_TO_UNIX_DAYS); retv *= SECSPERDAY; retv += (UINT32_C(1) << 31); return retv; } time_t basedate_get_erabase(void) { time_t retv; retv = (time_t)(s_baseday - NTP_TO_UNIX_DAYS); retv *= SECSPERDAY; return retv; } uint32_t basedate_get_gpsweek(void) { return s_gpsweek; } uint32_t basedate_expand_gpsweek( unsigned short weekno ) { /* We do a fast modulus expansion here. Since all quantities are * unsigned and we cannot go before the start of the GPS epoch * anyway, and since the truncated GPS week number is 10 bit, the * expansion becomes a simple sub/and/add sequence. */ #if GPSWEEKS != 1024 # error GPSWEEKS defined wrong -- should be 1024! #endif uint32_t diff; diff = ((uint32_t)weekno - s_gpsweek) & (GPSWEEKS - 1); return s_gpsweek + diff; } /* -*-EOF-*- */