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Fix Mbps pacing overflow on long replays #989

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Fix Mbps pacing overflow on long replays #989

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20 changes: 11 additions & 9 deletions src/send_packets.c
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Original file line number Diff line number Diff line change
Expand Up @@ -63,7 +63,7 @@ static void calc_sleep_time(tcpreplay_t *ctx,
sendpacket_t *sp,
COUNTER counter,
struct timespec *sent_timestamp,
COUNTER start_us,
COUNTER start_ns,
COUNTER *skip_length);
static void tcpr_sleep(tcpreplay_t *ctx, sendpacket_t *sp _U_, struct timespec *nap_this_time, struct timespec *now);
static u_char *get_next_packet(tcpreplay_opt_t *options,
Expand Down Expand Up @@ -1081,14 +1081,16 @@ calc_sleep_time(tcpreplay_t *ctx,
COUNTER tx_ns = now_ns - start_ns;

/*
* bits * 1000000000 divided by bps = nanosecond
*
* ensure there is no overflow in cases where bits_sent is very high
*/
if (bits_sent > COUNTER_OVERFLOW_RISK)
next_tx_ns = (bits_sent * 1000) / bps * 1000000;
else
next_tx_ns = (bits_sent * 1000000000) / bps;
* Calculate:
*
* next_tx_ns = bits_sent * 1000000000 / bps
*
* without multiplying the full bits_sent value by 1e9 first.
* That multiplication can overflow COUNTER on long low-rate replays,
* making next_tx_ns wrap small and causing skip_length to become huge.
*/
next_tx_ns = (bits_sent / bps) * 1000000000;
next_tx_ns += ((bits_sent % bps) * 1000000000) / bps;

if (next_tx_ns > tx_ns) {
NANOSEC_TO_TIMESPEC(next_tx_ns - tx_ns, &ctx->nap);
Expand Down