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Date: Tue, 01 Apr 2025 12:25:26 +0000
To: Javier Mateos <javierpmateos@gmail.com>
From: Pieter Wuille <bitcoin-dev@wuille.net>
Cc: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
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On Monday, March 31st, 2025 at 4:41 PM, Javier Mateos <javierpmateos@gmail.com> wrote:

> The solution of splitting the string and using OP_CAT only works if the exact position of the substring is known. How would a case be handled where the substring could be in any position

Whoever produces the signature/witness for spending the coin always knows the position already, so the script can always be modified to instead take that position as an additional input.

This is a general principle: the point of scripts is verifying provided information, not computing it. As another example, this means that there is no need for a division or square root opcode if one has a multiplication opcode.

--
Pieter

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<div style=3D"font-family: Arial, sans-serif; font-size: 14px;"><div><div>
        On Monday, March 31st, 2025 at 4:41 PM, Javier Mateos &lt;javierpma=
teos@gmail.com&gt; wrote:<br>
        <blockquote type=3D"cite"><div>
              The solution of splitting the string and using OP_CAT only
 works if the exact position of the substring is known. How would a case
 be handled where the substring could be in any position</div></blockquote>=
<div><br></div><div>Whoever
 produces the signature/witness for spending the coin always knows the=20
position already, so the script can always be modified to instead take=20
that position as an additional input.</div><div><br></div><div>This is a
 general principle: the point of scripts is verifying provided=20
information, not computing it. As another example, this means that there
 is no need for a division or square root opcode if one has a=20
multiplication opcode.</div><div><br></div><div>-- <br></div><div>Pieter</d=
iv><br></div></div></div>

<p></p>

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