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https://issues.apache.org/jira/browse/AVRO-2620?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16970890#comment-16970890
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ASF subversion and git services commented on AVRO-2620:
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Commit 96cfef55661fe2f29b89aa8b6813f94d06a62500 in avro's branch
refs/heads/master from Ryan Skraba
[ https://gitbox.apache.org/repos/asf?p=avro.git;h=96cfef5 ]
AVRO-2620: Use log power rule for max precision.
> Max precision on decimal/fixed LogicalType is wrong
> ---------------------------------------------------
>
> Key: AVRO-2620
> URL: https://issues.apache.org/jira/browse/AVRO-2620
> Project: Apache Avro
> Issue Type: Bug
> Components: c++, java
> Reporter: Ryan Skraba
> Assignee: Ryan Skraba
> Priority: Minor
>
> A decimal logical type with an underlying fixed bytes type is invalid if the
> precision is greater than can be contained in the fixed bytes. The
> calculation for
> [max
> precision|https://github.com/apache/avro/blob/a2098bd88361b5ff9298c462a2dccafbb0c2c508/lang/java/avro/src/main/java/org/apache/avro/LogicalTypes.java#L262]
> can return a wrong value when the fixed bytes size is greater than 128.
> For a fixed size of *129*, the {{Math.pow(2, 8 * size - 1)}} part of this
> formula will return {{Double.INFINITY}}, and the max precision will be
> considered {{Long.MAX_VALUE}}. The expected value is 310 digits precision.
> We can apply the log power rule to avoid overflow, or some bit-twiddling
> approximation (like
> [java.math.BigDecimal|https://github.com/openjdk/jdk/blob/jdk8-b120/jdk/src/share/classes/java/math/BigDecimal.java#L3779]).
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