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myarbrough@oreilly.com 2014-11-25 12:56:34 -08:00
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@ -293,9 +293,6 @@ Conditional operators evaluate a condition, producing a boolean result of TRUE o
In <<simplemath_script>>, the script +2 3 OP_ADD 5 OP_EQUAL+ demonstrates the arithmetic addition operator +OP_ADD+, adding two numbers and putting the result on the stack, followed by the conditional operator +OP_EQUAL+, which checks that the resulting sum is equal to +5+. For brevity, the +OP_+ prefix is omitted in the step-by-step example.
[[simplemath_script]]
.Bitcoin's script validation doing simple math
image::images/msbt_0502.png["TxScriptSimpleMathExample"]
The following is a slightly more complex script, which calculates ++2 + 7 – 3 + 1++. Notice that when the script contains several operators in a row, the stack allows the results of one operator to be acted upon by the next operator:
@ -324,10 +321,15 @@ The validation software combines the locking and unlocking scripts and the resul
As we saw in the step-by-step example in <<simplemath_script>>, when this script is executed, the result is +OP_TRUE+, making the transaction valid. Not only is this a valid transaction output locking script, but the resulting UTXO could be spent by anyone with the arithmetic skills to know that the number 2 satisfies the script.
[[simplemath_script]]
.Bitcoin's script validation doing simple math
image::images/msbt_0502.png["TxScriptSimpleMathExample"]
[TIP]
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Transactions are valid if the top result on the stack is TRUE (noted as +{0x01}+), any other non-zero value or if the stack is empty after script execution. Transactions are invalid if the top value on the stack is FALSE (a zero-length empty value, noted as +{}+) or if script execution is halted explicitly by an operator, such as OP_VERIFY, OP_RETURN or a conditional terminator such as OP_ENDIF. See <<tx_script_ops>> for details.(((range="endofrange", startref="ix_ch05-asciidoc14")))(((range="endofrange", startref="ix_ch05-asciidoc13")))
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==== Turing Incompleteness