/* $NetBSD: subr_time_arith.c,v 1.1 2024/12/22 23:24:20 riastradh Exp $ */ /*- * Copyright (c) 2000, 2004, 2005, 2007, 2008, 2009, 2020 * The NetBSD Foundation, Inc. * All rights reserved. * * This code is derived from software contributed to The NetBSD Foundation * by Christopher G. Demetriou, by Andrew Doran, and by Jason R. Thorpe. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ /* * Copyright (c) 1982, 1986, 1989, 1993 * The Regents of the University of California. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)kern_clock.c 8.5 (Berkeley) 1/21/94 * @(#)kern_time.c 8.4 (Berkeley) 5/26/95 */ #include __KERNEL_RCSID(0, "$NetBSD: subr_time_arith.c,v 1.1 2024/12/22 23:24:20 riastradh Exp $"); #include #include #include #include #if defined(_KERNEL) #include #include #include #elif defined(_TIME_TESTING) #include #include #include extern int hz; extern long tick; #define KASSERT assert #endif /* * Compute number of ticks in the specified amount of time. */ int tvtohz(const struct timeval *tv) { unsigned long ticks; long sec, usec; /* * If the number of usecs in the whole seconds part of the time * difference fits in a long, then the total number of usecs will * fit in an unsigned long. Compute the total and convert it to * ticks, rounding up and adding 1 to allow for the current tick * to expire. Rounding also depends on unsigned long arithmetic * to avoid overflow. * * Otherwise, if the number of ticks in the whole seconds part of * the time difference fits in a long, then convert the parts to * ticks separately and add, using similar rounding methods and * overflow avoidance. This method would work in the previous * case, but it is slightly slower and assumes that hz is integral. * * Otherwise, round the time difference down to the maximum * representable value. * * If ints are 32-bit, then the maximum value for any timeout in * 10ms ticks is 248 days. */ sec = tv->tv_sec; usec = tv->tv_usec; KASSERT(usec >= 0); KASSERT(usec < 1000000); /* catch overflows in conversion time_t->int */ if (tv->tv_sec > INT_MAX) return INT_MAX; if (tv->tv_sec < 0) return 0; if (sec < 0 || (sec == 0 && usec == 0)) { /* * Would expire now or in the past. Return 0 ticks. * This is different from the legacy tvhzto() interface, * and callers need to check for it. */ ticks = 0; } else if (sec <= (LONG_MAX / 1000000)) ticks = (((sec * 1000000) + (unsigned long)usec + (tick - 1)) / tick) + 1; else if (sec <= (LONG_MAX / hz)) ticks = (sec * hz) + (((unsigned long)usec + (tick - 1)) / tick) + 1; else ticks = LONG_MAX; if (ticks > INT_MAX) ticks = INT_MAX; return ((int)ticks); } /* * Check that a proposed value to load into the .it_value or * .it_interval part of an interval timer is acceptable, and * fix it to have at least minimal value (i.e. if it is less * than the resolution of the clock, round it up.). We don't * timeout the 0,0 value because this means to disable the * timer or the interval. */ int itimerfix(struct timeval *tv) { if (tv->tv_usec < 0 || tv->tv_usec >= 1000000) return EINVAL; if (tv->tv_sec < 0) return ETIMEDOUT; if (tv->tv_sec == 0 && tv->tv_usec != 0 && tv->tv_usec < tick) tv->tv_usec = tick; return 0; } int itimespecfix(struct timespec *ts) { if (ts->tv_nsec < 0 || ts->tv_nsec >= 1000000000) return EINVAL; if (ts->tv_sec < 0) return ETIMEDOUT; if (ts->tv_sec == 0 && ts->tv_nsec != 0 && ts->tv_nsec < tick * 1000) ts->tv_nsec = tick * 1000; return 0; } /* * timespecaddok(tsp, usp) * * True if tsp + usp can be computed without overflow, i.e., if it * is OK to do timespecadd(tsp, usp, ...). */ bool timespecaddok(const struct timespec *tsp, const struct timespec *usp) { enum { TIME_MIN = __type_min(time_t), TIME_MAX = __type_max(time_t) }; time_t a = tsp->tv_sec; time_t b = usp->tv_sec; bool carry; /* * Caller is responsible for guaranteeing valid timespec * inputs. Any user-controlled inputs must be validated or * adjusted. */ KASSERT(tsp->tv_nsec >= 0); KASSERT(usp->tv_nsec >= 0); KASSERT(tsp->tv_nsec < 1000000000L); KASSERT(usp->tv_nsec < 1000000000L); __CTASSERT(1000000000L <= __type_max(long) - 1000000000L); /* * Fail if a + b + carry overflows TIME_MAX, or if a + b * overflows TIME_MIN because timespecadd adds the carry after * computing a + b. * * Break it into two mutually exclusive and exhaustive cases: * I. a >= 0 * II. a < 0 */ carry = (tsp->tv_nsec + usp->tv_nsec >= 1000000000L); if (a >= 0) { /* * Case I: a >= 0. If b < 0, then b + 1 <= 0, so * * a + b + 1 <= a + 0 <= TIME_MAX, * * and * * a + b >= 0 + b = b >= TIME_MIN, * * so this can't overflow. * * If b >= 0, then a + b + carry >= a + b >= 0, so * negative results and thus results below TIME_MIN are * impossible; we need only avoid * * a + b + carry > TIME_MAX, * * which we will do by rejecting if * * b > TIME_MAX - a - carry, * * which in turn is incidentally always false if b < 0 * so we don't need extra logic to discriminate on the * b >= 0 and b < 0 cases. * * Since 0 <= a <= TIME_MAX, we know * * 0 <= TIME_MAX - a <= TIME_MAX, * * and hence * * -1 <= TIME_MAX - a - 1 < TIME_MAX. * * So we can compute TIME_MAX - a - carry (i.e., either * TIME_MAX - a or TIME_MAX - a - 1) safely without * overflow. */ if (b > TIME_MAX - a - carry) return false; } else { /* * Case II: a < 0. If b >= 0, then since a + 1 <= 0, * we have * * a + b + 1 <= b <= TIME_MAX, * * and * * a + b >= a >= TIME_MIN, * * so this can't overflow. * * If b < 0, then the intermediate a + b is negative * and the outcome a + b + 1 is nonpositive, so we need * only avoid * * a + b < TIME_MIN, * * which we will do by rejecting if * * a < TIME_MIN - b. * * (Reminder: The carry is added afterward in * timespecadd, so to avoid overflow it is not enough * to merely reject a + b + carry < TIME_MIN.) * * It is safe to compute the difference TIME_MIN - b * because b is negative, so the result lies in * (TIME_MIN, 0]. */ if (b < 0 && a < TIME_MIN - b) return false; } return true; } /* * timespecsubok(tsp, usp) * * True if tsp - usp can be computed without overflow, i.e., if it * is OK to do timespecsub(tsp, usp, ...). */ bool timespecsubok(const struct timespec *tsp, const struct timespec *usp) { enum { TIME_MIN = __type_min(time_t), TIME_MAX = __type_max(time_t) }; time_t a = tsp->tv_sec, b = usp->tv_sec; bool borrow; /* * Caller is responsible for guaranteeing valid timespec * inputs. Any user-controlled inputs must be validated or * adjusted. */ KASSERT(tsp->tv_nsec >= 0); KASSERT(usp->tv_nsec >= 0); KASSERT(tsp->tv_nsec < 1000000000L); KASSERT(usp->tv_nsec < 1000000000L); __CTASSERT(1000000000L <= __type_max(long) - 1000000000L); /* * Fail if a - b - borrow overflows TIME_MIN, or if a - b * overflows TIME_MAX because timespecsub subtracts the borrow * after computing a - b. * * Break it into two mutually exclusive and exhaustive cases: * I. a < 0 * II. a >= 0 */ borrow = (tsp->tv_nsec - usp->tv_nsec < 0); if (a < 0) { /* * Case I: a < 0. If b < 0, then -b - 1 >= 0, so * * a - b - 1 >= a + 0 >= TIME_MIN, * * and, since a <= -1, provided that TIME_MIN <= * -TIME_MAX - 1 so that TIME_MAX <= -TIME_MIN - 1 (in * fact, equality holds, under the assumption of * two's-complement arithmetic), * * a - b <= -1 - b = -b - 1 <= TIME_MAX, * * so this can't overflow. */ __CTASSERT(TIME_MIN <= -TIME_MAX - 1); /* * If b >= 0, then a - b - borrow <= a - b < 0, so * positive results and thus results above TIME_MAX are * impossible; we need only avoid * * a - b - borrow < TIME_MIN, * * which we will do by rejecting if * * a < TIME_MIN + b + borrow. * * The right-hand side is safe to evaluate for any * values of b and borrow as long as TIME_MIN + * TIME_MAX + 1 <= TIME_MAX, i.e., TIME_MIN <= -1. * (Note: If time_t were unsigned, this would fail!) * * Note: Unlike Case I in timespecaddok, this criterion * does not work for b < 0, nor can the roles of a and * b in the inequality be reversed (e.g., -b < TIME_MIN * - a + borrow) without extra cases like checking for * b = TEST_MIN. */ __CTASSERT(TIME_MIN < -1); if (b >= 0 && a < TIME_MIN + b + borrow) return false; } else { /* * Case II: a >= 0. If b >= 0, then * * a - b <= a <= TIME_MAX, * * and, provided TIME_MIN <= -TIME_MAX - 1 (in fact, * equality holds, under the assumption of * two's-complement arithmetic) * * a - b - 1 >= -b - 1 >= -TIME_MAX - 1 >= TIME_MIN, * * so this can't overflow. */ __CTASSERT(TIME_MIN <= -TIME_MAX - 1); /* * If b < 0, then a - b >= a >= 0, so negative results * and thus results below TIME_MIN are impossible; we * need only avoid * * a - b > TIME_MAX, * * which we will do by rejecting if * * a > TIME_MAX + b. * * (Reminder: The borrow is subtracted afterward in * timespecsub, so to avoid overflow it is not enough * to merely reject a - b - borrow > TIME_MAX.) * * It is safe to compute the sum TIME_MAX + b because b * is negative, so the result lies in [0, TIME_MAX). */ if (b < 0 && a > TIME_MAX + b) return false; } return true; } /* * itimer_transition(it, now, next, &overruns) * * Given: * * - it: the current state of an itimer (it_value = last expiry * time, it_interval = periodic rescheduling interval), and * * - now: the current time on the itimer's clock; * * compute: * * - next: the next time the itimer should be scheduled for, and * - overruns: the number of overruns if we're firing late. * * XXX This should maybe also say whether the itimer should expire * at all. */ void itimer_transition(const struct itimerspec *restrict it, const struct timespec *restrict now, struct timespec *restrict next, int *restrict overrunsp) { uint64_t last_val, next_val, interval, now_ns; int backwards; /* * Zero the outputs so we can test assertions in userland * without undefined behaviour. */ timespecclear(next); *overrunsp = 0; /* * Paranoia: Caller should guarantee this. */ if (!timespecisset(&it->it_interval)) { timespecclear(next); return; } backwards = (timespeccmp(&it->it_value, now, >)); /* Nonnegative interval guaranteed by itimerfix. */ KASSERT(it->it_interval.tv_sec >= 0); KASSERT(it->it_interval.tv_nsec >= 0); /* Handle the easy case of non-overflown timers first. */ if (!backwards && timespecaddok(&it->it_value, &it->it_interval)) { timespecadd(&it->it_value, &it->it_interval, next); } else { now_ns = timespec2ns(now); last_val = timespec2ns(&it->it_value); interval = timespec2ns(&it->it_interval); next_val = now_ns + (now_ns - last_val + interval - 1) % interval; if (backwards) next_val += interval; else *overrunsp = (now_ns - last_val) / interval; next->tv_sec = next_val / 1000000000; next->tv_nsec = next_val % 1000000000; } }