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diffcore-break: don't divide by zero

When the source file is empty, the calculation of the merge score
results in a division by zero.  In the situation:

     == preimage ==             == postimage ==

     F (empty file)             F (a large file)
                                E (a new empty file)

it does not make sense to consider F->E as a rename, so it is better not
to break the pre- and post-image of F.

Bail out early in this case to avoid hitting the divide-by-zero.  This
causes the merge score to be left at zero.

Signed-off-by: John Keeping <>
Signed-off-by: Junio C Hamano <>
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1 parent 1599999 commit e7b00c57640fa2bf11e4218b588f51cc5a9a754e @johnkeeping johnkeeping committed with gitster Apr 3, 2013
Showing with 3 additions and 0 deletions.
  1. +3 −0 diffcore-break.c
@@ -68,6 +68,9 @@ static int should_break(struct diff_filespec *src,
if (max_size < MINIMUM_BREAK_SIZE)
return 0; /* we do not break too small filepair */
+ if (!src->size)
+ return 0; /* we do not let empty files get renamed */
if (diffcore_count_changes(src, dst,
&src->cnt_data, &dst->cnt_data,

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