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annotate lib/timespec-sub.c @ 40057:b06060465f09

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maint: Run 'make update-copyright'
author Paul Eggert <eggert@cs.ucla.edu>
date Tue, 01 Jan 2019 00:25:11 +0100
parents 4c9d0c898076
children
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1 /* Subtract two struct timespec values.
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2
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3 Copyright (C) 2011-2019 Free Software Foundation, Inc.
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4
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5 This program is free software: you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation; either version 3 of the License, or
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8 (at your option) any later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
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17
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18 /* Written by Paul Eggert. */
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19
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20 /* Return the difference between two timespec values A and B. On
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21 overflow, return an extremal value. This assumes 0 <= tv_nsec <
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22 TIMESPEC_HZ. */
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23
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24 #include <config.h>
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25 #include "timespec.h"
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26
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27 #include "intprops.h"
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28
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29 struct timespec
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30 timespec_sub (struct timespec a, struct timespec b)
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31 {
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32 time_t rs = a.tv_sec;
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33 time_t bs = b.tv_sec;
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34 int ns = a.tv_nsec - b.tv_nsec;
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35 int rns = ns;
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36 time_t tmin = TYPE_MINIMUM (time_t);
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37 time_t tmax = TYPE_MAXIMUM (time_t);
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38
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39 if (ns < 0)
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40 {
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41 rns = ns + TIMESPEC_HZ;
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42 if (bs < tmax)
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43 bs++;
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44 else if (- TYPE_SIGNED (time_t) < rs)
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45 rs--;
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46 else
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47 goto low_overflow;
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48 }
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49
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50 /* INT_SUBTRACT_WRAPV is not appropriate since time_t might be unsigned.
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51 In theory time_t might be narrower than int, so plain
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52 INT_SUBTRACT_OVERFLOW does not suffice. */
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53 if (! INT_SUBTRACT_OVERFLOW (rs, bs) && tmin <= rs - bs && rs - bs <= tmax)
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54 rs -= bs;
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55 else
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56 {
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57 if (rs < 0)
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58 {
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59 low_overflow:
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60 rs = tmin;
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61 rns = 0;
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62 }
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63 else
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64 {
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65 rs = tmax;
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66 rns = TIMESPEC_HZ - 1;
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67 }
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68 }
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69
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70 return make_timespec (rs, rns);
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71 }