BIP-345: add sigops cost of 60

Author: jamesob

bip-0345.mediawiki

@@ -266,6 +266,7 @@ where
 
 After the stack is parsed, the following validation checks are performed:
 
+* Decrement the per-script sigops budget (see [https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki#user-content-Resource_limits BIP-0342]) by 60<ref>'''Why is the sigops cost for OP_VAULT set to 60?''' To determine the validity of a trigger output, OP_VAULT must perform an EC multiplication and hashing proportional to the length of the control block in order to generate the output's expected TapTweak. This has been measured to have a cost in the worst case (max length control block) of roughly twice a Schnorr verification. Because the hashing cost could be mitigated by caching midstate, the cost is 60 and not 100.</ref>; if the budget is brought below zero, script execution MUST fail and terminate immediately.
 * Let the output designated by <code><trigger-vout-idx></code> be called ''triggerOut''.
 * If the scriptPubKey of ''triggerOut'' is not a witness program of the same version and same tapleaf version as the currently executing script, script execution MUST fail and terminate immediately.
 * Let the script constructed by taking the <code><leaf-update-script-body></code> and prefixing it with minimally-encoded data pushes of the <code><n-pushes></code> leaf-update script data items be called the ''leaf-update-script''.