98 lines
3.6 KiB
C
98 lines
3.6 KiB
C
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ This program is free software; you can redistribute it and/or modify │
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│ it under the terms of the GNU General Public License as published by │
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│ the Free Software Foundation; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ General Public License for more details. │
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│ │
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│ You should have received a copy of the GNU General Public License │
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│ along with this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/bits/bits.h"
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#include "libc/bits/initializer.h"
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#include "libc/bits/safemacros.h"
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#include "libc/calls/calls.h"
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#include "libc/dce.h"
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#include "libc/nexgen32e/rdtsc.h"
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#include "libc/nexgen32e/x86feature.h"
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#include "libc/sysv/consts/clock.h"
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#include "libc/time/time.h"
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static struct Now {
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bool once;
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uint64_t k0;
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long double r0, cpn;
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} now_;
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/**
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* Returns timestamp without needing system calls.
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* @note uses microsecond scale fallback on k8 or vm
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*/
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long double (*nowl)(void);
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static long double GetTimeSample(void) {
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uint64_t tick1, tick2;
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long double time1, time2;
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sched_yield();
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time1 = dtime(CLOCK_MONOTONIC);
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tick1 = rdtsc();
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nanosleep(&(struct timespec){0, 100000}, NULL);
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time2 = dtime(CLOCK_MONOTONIC);
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tick2 = rdtsc();
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return (time2 - time1) * 1e9 / (tick2 - tick1);
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}
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static long double MeasureNanosPerCycle(void) {
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int i;
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long double avg, samp;
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for (avg = 1.0L, i = 1; i < 5; ++i) {
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samp = GetTimeSample();
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avg += (samp - avg) / i;
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}
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return avg;
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}
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static void InitTime(void) {
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now_.cpn = MeasureNanosPerCycle();
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now_.r0 = dtime(CLOCK_REALTIME);
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now_.k0 = rdtsc();
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now_.once = true;
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}
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long double converttickstonanos(uint64_t ticks) {
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if (!now_.once) InitTime();
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return ticks * now_.cpn; /* pico scale */
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}
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long double converttickstoseconds(uint64_t ticks) {
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return 1 / 1e9 * converttickstonanos(ticks);
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}
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long double nowl$sys(void) {
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return dtime(CLOCK_REALTIME);
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}
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long double nowl$art(void) {
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uint64_t ticks;
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if (!now_.once) InitTime();
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ticks = unsignedsubtract(rdtsc(), now_.k0);
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return now_.r0 + converttickstoseconds(ticks);
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}
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INITIALIZER(301, _init_nowl, {
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if (X86_HAVE(INVTSC)) {
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nowl = nowl$art;
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} else {
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nowl = nowl$sys;
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}
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})
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