128 lines
3.9 KiB
C
128 lines
3.9 KiB
C
#include "ulib.h"
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/*
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* Real ring-3 "date": the first live demo of rtc.c/sysTime's wall-clock
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* time, spawned directly by kmain.c at boot exactly like nicetest.c above
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* it -- fully synchronous, no injected keystroke or pipe rendezvous, so
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* unlike most of this kernel's live demos this one has no scheduling-
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* timing race to flake on at all.
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*
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* Deliberately duplicates (not shares) Howard Hinnant's civil-calendar
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* algorithm rtc.c already uses: this file writes its OWN forward
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* (civil -> epoch) and inverse (epoch -> civil) implementations from
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* scratch, independent of the kernel side. Decoding the epoch userTime()
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* returns and then re-encoding it back with this independent forward
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* function must reproduce the exact same number, which proves this
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* program's own encode/decode pair is a true bijection over the date it
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* actually ran on -- a real, self-verifying round trip, not a print
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* nobody checks.
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*/
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static void printErr(const char* text)
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{
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userWrite(2, text, stringLength(text));
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}
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/* Zero-padded unsigned decimal, `width` digits minimum (e.g. printPadded(7, 2)
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-> "07"). Never negative here -- every field this file ever passes in is
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already a non-negative calendar component. */
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static void printPadded(long value, int width)
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{
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char digits[16];
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int len = 0;
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long remaining = value;
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if (remaining == 0)
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digits[len++] = '0';
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while (remaining > 0) {
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digits[len++] = (char)('0' + (remaining % 10));
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remaining /= 10;
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}
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while (len < width)
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digits[len++] = '0';
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for (int i = len - 1; i >= 0; i--)
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userWrite(1, &digits[i], 1);
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}
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/* Howard Hinnant's days_from_civil -- forward direction, civil date to a
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day count relative to 1970-01-01. See rtc.c for the same algorithm used
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kernel-side; this copy is independent, not shared, on purpose (see file
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header comment). */
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static long daysFromCivil(long y, long m, long d)
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{
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y -= (m <= 2) ? 1 : 0;
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long era = (y >= 0 ? y : y - 399) / 400;
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long yoe = y - era * 400;
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long doy = (153 * (m + (m > 2 ? -3 : 9)) + 2) / 5 + d - 1;
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long doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;
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return era * 146097 + doe - 719468;
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}
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/* Howard Hinnant's civil_from_days -- the inverse direction, a day count
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back to a civil date. */
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static void civilFromDays(long z, long* outYear, long* outMonth, long* outDay)
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{
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z += 719468;
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long era = (z >= 0 ? z : z - 146096) / 146097;
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long doe = z - era * 146097;
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long yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
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long yy = yoe + era * 400;
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long doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
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long mp = (5 * doy + 2) / 153;
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long dd = doy - (153 * mp + 2) / 5 + 1;
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long mm = mp + (mp < 10 ? 3 : -9);
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*outYear = yy + (mm <= 2 ? 1 : 0);
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*outMonth = mm;
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*outDay = dd;
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}
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int main(void)
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{
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long epoch = userTime();
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if (epoch <= 0) {
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printErr("date: FAIL sysTime returned a non-positive epoch\n");
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return 1;
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}
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long days = epoch / 86400;
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long secondsOfDay = epoch % 86400;
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long hour = secondsOfDay / 3600;
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long minute = (secondsOfDay % 3600) / 60;
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long second = secondsOfDay % 60;
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long year;
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long month;
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long day;
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civilFromDays(days, &year, &month, &day);
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if (year < 2020 || year > 2099) {
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printErr("date: FAIL implausible year decoded\n");
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return 1;
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}
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printPadded(year, 4);
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userWrite(1, "-", 1);
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printPadded(month, 2);
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userWrite(1, "-", 1);
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printPadded(day, 2);
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userWrite(1, " ", 1);
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printPadded(hour, 2);
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userWrite(1, ":", 1);
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printPadded(minute, 2);
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userWrite(1, ":", 1);
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printPadded(second, 2);
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userWrite(1, "\n", 1);
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printErr("date: printed-ok\n");
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long roundTrip = daysFromCivil(year, month, day) * 86400 + hour * 3600 + minute * 60 + second;
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if (roundTrip != epoch) {
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printErr("date: FAIL roundtrip mismatch\n");
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return 1;
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}
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printErr("date: roundtrip-ok\n");
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return 0;
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}
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