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55 lines
2.9 KiB
C
55 lines
2.9 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/calls/struct/timespec.h"
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#include "libc/limits.h"
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#include "libc/stdckdint.h"
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/**
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* Reduces `ts` from 1e-9 to 1e-3 granularity w/ ceil rounding.
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*
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* This function uses ceiling rounding. For example, if `ts` is one
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* nanosecond, then one millisecond will be returned. Ceil rounding
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* is needed by many interfaces, e.g. setitimer(), because the zero
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* timestamp has a special meaning.
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*
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* This function also detects overflow in which case `INT64_MAX` or
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* `INT64_MIN` may be returned. The `errno` variable isn't changed.
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*
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* @return 64-bit scalar milliseconds since epoch
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*/
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int64_t timespec_tomillis(struct timespec ts) {
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int64_t ms;
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// reduce precision from nanos to millis
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if (ts.tv_nsec <= 999000000) {
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ts.tv_nsec = (ts.tv_nsec + 999999) / 1000000;
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} else {
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ts.tv_nsec = 0;
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if (ts.tv_sec < INT64_MAX) {
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ts.tv_sec += 1;
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}
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}
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// convert to scalar result
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if (!ckd_mul(&ms, ts.tv_sec, 1000ul) && !ckd_add(&ms, ms, ts.tv_nsec)) {
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return ms;
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} else if (ts.tv_sec < 0) {
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return INT64_MIN;
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} else {
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return INT64_MAX;
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}
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}
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