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Bug #3521

closed

Incorrect sign-extension in EXPath binary bin:unpack(-unsigned)-integer()

Added by John Lumley over 6 years ago. Updated about 1 year ago.

Status:
Closed
Priority:
Normal
Assignee:
Category:
EXSLT extensions
Sprint/Milestone:
-
Start date:
2017-11-12
Due date:
% Done:

0%

Estimated time:
Legacy ID:
Applies to branch:
9.6, 9.7, 9.8, trunk
Fix Committed on Branch:
Fixed in Maintenance Release:
Platforms:

Description

Logged by T Hata in https://saxonica.plan.io/boards/3/topics/7053:

Errors in unpacking binary integers with high bit set:

<unpack b="8000000000000000">
   <signed>
      <int size="0">0</int>
      <int size="1">-128</int>
      <int size="2">-32768</int>
      <int size="3">-8388608</int>
      <int size="4">-1</int>
      <int size="5">-256</int>
      <int size="6">-65536</int>
      <int size="7">-16777216</int>
      <int size="8">-1</int>
   </signed>
   <unsigned>
      <int size="0">0</int>
      <int size="1">128</int>
      <int size="2">32768</int>
      <int size="3">8388608</int>
      <int size="4">2147483648</int>
      <int size="5">549755813888</int>
      <int size="6">140737488355328</int>
      <int size="7">36028797018963968</int>
      <int size="8">-9223372036854775808</int>
   </unsigned>
</unpack>

It turns out that internally an int constant, rather than a long is used during sign extension calculation, which accounts for the error at 32-bit negative. The issue at 64 bit results from the sign extension or problems of holding an unsigned long with the top bit set. This has been changed so that Big representations are used above 7 byte unpacks.

Note that one of the EXPath QT3 tests, EXPath-binary-unpack-unsigned-integer-012, which unpacks all 64 bits set, has an incorrect assertion of value == -1, whereas it should be 18446744073709551615

Actions #1

Updated by John Lumley over 6 years ago

  • Status changed from New to Resolved

Patches committed to 9.7, 9.8 and trunk.

This bug has been lying dormant fot 4.5 years!

Actions #2

Updated by O'Neil Delpratt about 1 year ago

  • Description updated (diff)
  • Status changed from Resolved to Closed

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