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Modify comments about the precision

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conanoc
2018-05-24 17:06:44 +09:00
committed by Christian Decker
parent b28d71a9a5
commit c20e859f05
1 changed files with 4 additions and 7 deletions
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11
lightningd/payalgo.c
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@@ -429,13 +429,10 @@ static void json_pay_getroute_reply(struct subd *gossip UNUSED,
msatoshi_sent = route[0].amount; msatoshi_sent = route[0].amount;
fee = msatoshi_sent - pay->msatoshi; fee = msatoshi_sent - pay->msatoshi;
/* FIXME: IEEE Double-precision floating point has only 53 bits /* Casting u64 to double will lose some precision. The loss of precision
* of precision. Total satoshis that can ever be created is * in feepercent will be like 3.0000..(some dots)..1 % - 3.0 %.
* slightly less than 2100000000000000. Total msatoshis that * That loss will not be representable in double. So, it's Okay to
* can ever be created is 1000 times that or * cast u64 to double for feepercent calculation. */
* 2100000000000000000, requiring 60.865 bits of precision,
* and thus losing precision in the below. Currently, OK, as,
* payments are limited to 4294967295 msatoshi. */
feepercent = ((double) fee) * 100.0 / ((double) pay->msatoshi); feepercent = ((double) fee) * 100.0 / ((double) pay->msatoshi);
fee_too_high = (feepercent > pay->maxfeepercent); fee_too_high = (feepercent > pay->maxfeepercent);
delay_too_high = (route[0].delay > pay->maxdelay); delay_too_high = (route[0].delay > pay->maxdelay);