40 lines
1.2 KiB
C
40 lines
1.2 KiB
C
/* Copyright (c) 2017 LiteSpeed Technologies Inc. See LICENSE. */
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/*
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* lsquic_rtt.c -- RTT calculation
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*/
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#include <stdlib.h>
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#include <string.h>
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#include <sys/time.h>
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#include "lsquic_int_types.h"
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#include "lsquic_rtt.h"
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/* See RFC 2988 */
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#define ALPHA_SHIFT 3 /* Alpha is 1/8 */
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#define BETA_SHIFT 2 /* Beta is 1/4 */
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void
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lsquic_rtt_stats_update (struct lsquic_rtt_stats *stats,
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lsquic_time_t send_delta, lsquic_time_t lack_delta)
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{
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if (send_delta > lack_delta)
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send_delta -= lack_delta;
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if (stats->srtt) {
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stats->rttvar -= stats->rttvar >> BETA_SHIFT;
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// FIXED: subtracting unsigned (the (int) cast gets repromoted to uint64_t
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// made abs() irrelevant and allowed overflow. instead cast the difference
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// to a signed int64 and use labs() to get abs val.
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stats->rttvar += (llabs((int64_t) (send_delta - stats->srtt)))
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>> BETA_SHIFT;
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stats->srtt -= stats->srtt >> ALPHA_SHIFT;
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stats->srtt += send_delta >> ALPHA_SHIFT;
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} else {
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/* First measurement */
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stats->srtt = send_delta;
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stats->rttvar = send_delta >> 1;
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}
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}
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