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fixed htlc weight calculation

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pm47 2017-02-09 16:33:34 +01:00 • committed by Rusty Russell
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03-transactions.md
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@ -239,8 +239,8 @@ Thus we use a simplified formula for *expected weight*, which assumes:
This gives us the following *expected weights* (details of the computation in [Appendix A](#appendix-a-expected-weights)):
Commitment weight: 724 + 172 * num-untrimmed-htlc-outputs
HTLC-timeout weight: 634
HTLC-success weight: 671
HTLC-timeout weight: 635
HTLC-success weight: 673
Note that we refer to the "base fee" for a commitment transaction in the requirements below, which is what the funder pays. The actual fee may be higher than the amount calculated here, due to rounding and trimmed outputs.
@ -248,11 +248,11 @@ Note that we refer to the "base fee" for a commitment transaction in the require
The fee for an HTLC-timeout transaction MUST BE calculated to match:
1. Multiply `feerate-per-kw` by 634 and divide by 1000 (rounding down).
1. Multiply `feerate-per-kw` by 635 and divide by 1000 (rounding down).
The fee for an HTLC-success transaction MUST BE calculated to match:
1. Multiply `feerate-per-kw` by 671 and divide by 1000 (rounding down).
1. Multiply `feerate-per-kw` by 673 and divide by 1000 (rounding down).
The base fee for a commitment transaction MUST BE calculated to match:
@ -269,26 +269,26 @@ For example, suppose that we have a `feerate-per-kw` of 5000, a `dust-limit-sato
* 2 offered HTLCs of 5000000 and 1000000 millisatoshis (5000 and 1000 satoshis)
* 2 received HTLCs of 7000000 and 800000 millisatoshis (7000 and 800 satoshis)
The HTLC timeout transaction weight is 634, thus fee would be 3170 satoshis.
The HTLC success transaction weight is 671, thus fee would be 3355 satoshis
The HTLC timeout transaction weight is 635, thus fee would be 3175 satoshis.
The HTLC success transaction weight is 673, thus fee would be 3365 satoshis
The commitment transaction weight would be calculated as follows:
* weight starts at 724.
* The offered HTLC of 5000 satoshis is above 546 + 3170 and would result in:
* The offered HTLC of 5000 satoshis is above 546 + 3175 and would result in:
* an output of 5000 satoshi in the commitment transaction
* a HTLC timeout transaction of 5000 - 3170 satoshis which spends this output
* a HTLC timeout transaction of 5000 - 3175 satoshis which spends this output
* weight increases to 896
* The offered HTLC of 1000 satoshis is below 546 + 3710, so would be trimmed.
* The offered HTLC of 1000 satoshis is below 546 + 3175, so would be trimmed.
* The received HTLC of 7000 satoshis is above 546 + 3355 and would result in:
* The received HTLC of 7000 satoshis is above 546 + 3365 and would result in:
* an output of 7000 satoshi in the commitment transaction
* a HTLC success transaction of 7000 - 3355 satoshis which spends this output
* a HTLC success transaction of 7000 - 3365 satoshis which spends this output
* weight increases to 1068
* The received HTLC of 800 satoshis is below 546 + 3355 so would be trimmed.
* The received HTLC of 800 satoshis is below 546 + 3365 so would be trimmed.
The base commitment transaction fee would be 5340 satoshi; the actual
fee (adding the 1000 and 800 satoshi HTLCs which would have made dust
@ -588,11 +588,12 @@ Multiplying non-witness data by 4, this gives a weight of:
The *expected weight* of an HTLC transaction is calculated as follows:
accepted_htlc_script: 109 bytes
accepted_htlc_script: 111 bytes
- OP_DATA: 1 byte (remotekey length)
- remotekey: 33 bytes
- OP_SWAP: 1 byte
- OP_SIZE: 1 byte
- OP_DATA: 1 byte (32 length)
- 32: 1 byte
- OP_EQUAL: 1 byte
- OP_IF: 1 byte
@ -608,18 +609,19 @@ The *expected weight* of an HTLC transaction is calculated as follows:
- OP_CHECKMULTISIG: 1 byte
- OP_ELSE: 1 byte
- OP_DROP: 1 byte
- OP_PUSHDATA2: 1 byte (locktime length)
- locktime: 2 bytes
- OP_DATA: 1 byte (locktime length)
- locktime: 3 bytes
- OP_CHECKLOCKTIMEVERIFY: 1 byte
- OP_DROP: 1 byte
- OP_CHECKSIG: 1 byte
- OP_ENDIF: 1 byte
offered_htlc_script: 104 bytes
offered_htlc_script: 105 bytes
- OP_DATA: 1 byte (remotekey length)
- remotekey: 33 bytes
- OP_SWAP: 1 byte
- OP_SIZE: 1 byte
- OP_DATA: 1 byte (32 length)
- 32: 1 byte
- OP_EQUAL: 1 byte
- OP_NOTIF: 1 byte
@ -638,7 +640,7 @@ The *expected weight* of an HTLC transaction is calculated as follows:
- OP_CHECKSIG: 1 byte
- OP_ENDIF: 1 byte
timeout_witness: 256 bytes
timeout_witness: 257 bytes
- number_of_witness_elements: 1 byte
- nil_length: 1 byte
- sig_alice_length: 1 byte
@ -649,7 +651,7 @@ The *expected weight* of an HTLC transaction is calculated as follows:
- witness_script_length: 1 byte
- witness_script (offered_htlc_script)
success_witness: 293 bytes
success_witness: 295 bytes
- number_of_witness_elements: 1 byte
- nil_length: 1 byte
- sig_alice_length: 1 byte
@ -687,11 +689,11 @@ The *expected weight* of an HTLC transaction is calculated as follows:
- lock_time: 4 bytes
Multiplying non-witness data by 4, this gives a weight of 376. Adding
the witness data for each case (256 + 2 for HTLC-timeout, 293 + 2 for
the witness data for each case (257 + 2 for HTLC-timeout, 295 + 2 for
HTLC-success) gives a weight of:
634 (HTLC-timeout)
671 (HTLC-success)
635 (HTLC-timeout)
673 (HTLC-success)
# Appendix C: Funding Transaction Test Vectors