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script opcode count IF vs. VERIFY: diff is two ops

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v1: HASH160 <expected hash> EQUALVERIFY <Bob's Pubkey> CHECKSIG
v2: HASH160 <expected hash> EQUAL IF <Bob's Pubkey> CHECKSIG ENDIF

ignoring the push-data ops (hash, pubkey),
v1 consists of [HASH160, EQUALVERIFY, CHECKSIG] -> 3 opcodes,
v2 consists of [HASH160, EQUAL, IF, CHECKSIG, ENDIF] -> 5 opcodes,
hence the difference is two opcodes.
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theStack 2018-02-05 14:23:38 -05:00
parent 1ac8b375e6
commit cf87badbd2
1 changed files with 1 additions and 1 deletions
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@ -498,7 +498,7 @@ Bob's unlocking script is identical:
<Bob's Sig> <hash pre-image>
----
The script with +IF+ does the same thing as using an opcode with a +VERIFY+ suffix; they both operate as guard clauses. However, the +VERIFY+ construction is more efficient, using one fewer opcode.
The script with +IF+ does the same thing as using an opcode with a +VERIFY+ suffix; they both operate as guard clauses. However, the +VERIFY+ construction is more efficient, using two fewer opcodes.
So, when do we use +VERIFY+ and when do we use +IF+? If all we are trying to do is to attach a precondition (guard clause), then +VERIFY+ is better. If, however, we want to have more than one execution path (flow control), then we need an +IF...ELSE+ flow control clause.