Subject: [PATCH 2/4] Remove silent clamp of renameLimit

From: Elijah Newren <[email-masked]>
Date: Fri, 10 Nov 2017 09:39:54 -0800

In commit 0024a5492 (Fix the rename detection limit checking; 2007-09-14),
the renameLimit was clamped to 32767.  This appears to have been to simply
avoid integer overflow in the following computation:

   num_create * num_src <= rename_limit * rename_limit

although it also could be viewed as a hardcoded bound on the amount of CPU
time we're willing to allow users to tell git to spend on handling
renames.  An upper bound may make sense, particularly as the computation
is O(rename_limit^2), but only if the bound is documented and communicated
to the user -- neither of which were true.

In fact, the silent clamping of the renameLimit to a smaller value and
lack of reporting of the needed renameLimit when it was too large made it
appear to the user as though they had used a high enough value; however,
git would proceed to mess up the merge or cherry-pick badly based on the
lack of rename detection.  Some hardy folks, despite the lack of feedback
on the correct limit to choose, were desperate enough to repeatedly retry
their cherry-picks with increasingly larger renameLimit values (going
orders of magnitude beyond the built-in limit of 32767), but were
consistently met with the same failure.

Although large limits can make things slow, we have users who would be
ecstatic to have a small five file change be correctly cherry picked even
if they have to manually specify a large limit and it took git ten minutes
to compute it.

Signed-off-by: Elijah Newren <[email-masked]>
---
 diff.c            |  2 +-
 diffcore-rename.c | 11 ++++-------
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/diff.c b/diff.c
index 6fd288420b..c6597e3231 100644
--- a/diff.c
+++ b/diff.c
@@ -5524,7 +5524,7 @@ void diff_warn_rename_limit(const char *varname, int needed, int degraded_cc)
 		warning(_(rename_limit_warning));
 	else
 		return;
-	if (0 < needed && needed < 32767)
+	if (0 < needed)
 		warning(_(rename_limit_advice), varname, needed);
 }
 
diff --git a/diffcore-rename.c b/diffcore-rename.c
index 0d8c3d2ee4..7f9a463f5a 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -391,14 +391,10 @@ static int too_many_rename_candidates(int num_create,
 	 * growing larger than a "rename_limit" square matrix, ie:
 	 *
 	 *    num_create * num_src > rename_limit * rename_limit
-	 *
-	 * but handles the potential overflow case specially (and we
-	 * assume at least 32-bit integers)
 	 */
-	if (rename_limit <= 0 || rename_limit > 32767)
-		rename_limit = 32767;
 	if ((num_create <= rename_limit || num_src <= rename_limit) &&
-	    (num_create * num_src <= rename_limit * rename_limit))
+	    ((double)num_create * (double)num_src
+	     <= (double)rename_limit * (double)rename_limit))
 		return 0;
 
 	options->needed_rename_limit =
@@ -415,7 +411,8 @@ static int too_many_rename_candidates(int num_create,
 		num_src++;
 	}
 	if ((num_create <= rename_limit || num_src <= rename_limit) &&
-	    (num_create * num_src <= rename_limit * rename_limit))
+	    ((double)num_create * (double)num_src
+	     <= (double)rename_limit * (double)rename_limit))
 		return 2;
 	return 1;
 }
-- 
2.15.0.5.g9567be9905