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Submission Summary: 0 pending, 1 declined, 0 accepted (1 total, 0.00% accepted)

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Microsoft

Submission + - Excel 2007 Multiplication Bug reverse-engineered

finnw writes: Research scientist Chris Lomont has analyzed in depth the Excel 2007 "65535" bug. Summary from the article:

This note:
  1. details how the bug works,
  2. shows the bug is a rendering bug, not a math error as many reported,
  3. shows how it was likely introduced by comparison to Excel 2002 and Excel 2000 behavior (the bug seems to have been inserted when updating an older 16-bit formatting routine to a 32-bit equivalent),
  4. explains how the just released hotfix corrects the behavior, confirming the analysis of the bug,
  5. and demonstrates why exactly twelve values out of more than 9*10^18 (approx 2^63) possible 64-bit floating-point values suffer from this bug.
One interesting point is that the affected routine appears to be written in x86 assembly language. Fortunately it doesn't appear to have caused a security hole.

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