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Overview
Comment:Correct the rollback journal checksum algorithm description.
Timelines: family | ancestors | descendants | both | trunk
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SHA1: b69eaea91403ec48d9559db9c3635d9d7f7f0ca7
User & Date: drh 2017-02-15 22:43:23
Context
2017-02-15
22:44
Fix a harmless typo in the rollback journal checksum algorithm description. check-in: ebd7ef38cc user: drh tags: trunk
22:43
Correct the rollback journal checksum algorithm description. check-in: b69eaea914 user: drh tags: trunk
2017-02-14
20:18
Enhanced documentation for the ".separator" and ".mode quote" commands in the CLI. check-in: 95afd54c2e user: drh tags: trunk
Changes
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Changes to pages/fileformat2.in.

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<p>^(The checksum is an unsigned 32-bit integer computed as follows:</p>

<ol>
<li>Initialize the checksum to the checksum nonce value found in the
journal header at offset 12.
<li>Initialize index X to be N-200 (where N is the size of a database page
in bytes.
<li>Interpret the four bytes at offset X into the page as a 4-byte big-endian
unsigned integer.  Add the value of that integer to the checksum.
<li>Subtrace 200 from X.
<li>If X is greater than or equal to zero, go back to step 3.
</ol>)^

<p>The checksum value is used to guard against incomplete writes of
a journal page record following a power failure.  A different random nonce
is used each time a transaction is started in order to minimize the risk







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<p>^(The checksum is an unsigned 32-bit integer computed as follows:</p>

<ol>
<li>Initialize the checksum to the checksum nonce value found in the
journal header at offset 12.
<li>Initialize index X to be N-200 (where N is the size of a database page
in bytes.
<li>Interpret the byte at offset X into the page as an 8-bit unsigned integer
 and add the value of that integer to the checksum.
<li>Subtrace 200 from X.
<li>If X is greater than or equal to zero, go back to step 3.
</ol>)^

<p>The checksum value is used to guard against incomplete writes of
a journal page record following a power failure.  A different random nonce
is used each time a transaction is started in order to minimize the risk