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https://issues.apache.org/jira/browse/OAK-6164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15996899#comment-15996899
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Matt Ryan commented on OAK-6164:
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[~mduerig] I wondered about doing that also. The problem is that there will
always be a range of values for which we can't compute the next highest power
of two, for any integer type. However, it may work to accept an {{int}} as the
input but return a {{long}} as the output.
For any value in the range [0x40000001, 0x7FFFFFFF], the next highest power of
2 would be 0x80000000. Interpreted as an {{int}} value this is actually
{{Integer.MIN_VALUE}} because of the sign bit, but this of course works as a
{{long}}. So this can work for all valid positive {{int}} input values. But
if the caller were to cast the result back to an {{int}} they would then end up
with a negative number (--2147483648) even though the {{long}} value is a
positive value (2147483648).
So that's a minor problem, but I think your point is that this would be better
than not accepting all valid positive {{int}} values and throwing an exception
when the range is exceeded. I tend to agree.
I'll make another patch.
> IOUtils.nextPowerOf2() returns lower power of 2 for very high int values
> ------------------------------------------------------------------------
>
> Key: OAK-6164
> URL: https://issues.apache.org/jira/browse/OAK-6164
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: commons
> Reporter: Matt Ryan
> Assignee: Michael Dürig
> Priority: Minor
> Fix For: 1.7.0, 1.8
>
> Attachments: OAK-6164.patch.1, OAK-6164.patch.2
>
>
> In the IOUtils.nextPowerOf2() method, all int values are accepted as input.
> However, there are valid signed integer values that this method accepts as
> input, but for which a lower power of 2 value is returned.
> This occurs for values that are valid signed integer values that are greater
> than the highest possible power of two value in the signed integer range.
> Signed integer values have the maximum value of 0x7FFFFFFF, but the maximum
> possible power of two in the signed integer range is 0x40000000. (The
> current implementation incorrectly identifies the maximum possible power of
> two as 0x3FFFFFFF, due to how it is computed by doing integer division of
> 0x7FFFFFFF / 2.)
> In the current implementation any input in the range of [0x40000000,
> 0x7FFFFFFF] is a valid signed integer input, but the method will return
> 0x3FFFFFFF as the next valid max power of 2.
> Two minor things need to be fixed:
> * If the input is 0x40000000, the return value needs to be 0x40000000,
> instead of 0x3FFFFFFF which is not a valid power of 2.
> * If the input is in the range [0x40000001, 0x7FFFFFFF] I propose the method
> should instead throw an IllegalArgumentException and indicate that it is not
> possible to compute a next power of 2 for a number in that range.
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