diffcore-rename: simplify limit check

diffcore-rename had two different checks of the form

    if ((a < limit || b < limit) &&
        a * b <= limit * limit)

This can be simplified to

    if (st_mult(a, b) <= st_mult(limit, limit))

which makes it clearer how we are checking for overflow, and makes it
much easier to parse given the drop from 8 to 4 variable appearances.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 1d6675c040df37e9df7be83f4baaf1bcb123b902..16553ab259f166154f9b13d5acdcc006344a161b 100644 (file)
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -447,12 +447,16 @@ static int too_many_rename_candidates(int num_destinations, int num_sources,
         * growing larger than a "rename_limit" square matrix, ie:
         *
         *    num_destinations * num_sources > rename_limit * rename_limit
+        *
+        * We use st_mult() to check overflow conditions; in the
+        * exceptional circumstance that size_t isn't large enough to hold
+        * the multiplication, the system won't be able to allocate enough
+        * memory for the matrix anyway.
         */
        if (rename_limit <= 0)
                rename_limit = 32767;
-       if ((num_destinations <= rename_limit || num_sources <= rename_limit) &&
-           ((uint64_t)num_destinations * (uint64_t)num_sources
-            <= (uint64_t)rename_limit * (uint64_t)rename_limit))
+       if (st_mult(num_destinations, num_sources)
+           <= st_mult(rename_limit, rename_limit))
                return 0;
 
        options->needed_rename_limit =
@@ -468,9 +472,8 @@ static int too_many_rename_candidates(int num_destinations, int num_sources,
                        continue;
                limited_sources++;
        }
-       if ((num_destinations <= rename_limit || limited_sources <= rename_limit) &&
-           ((uint64_t)num_destinations * (uint64_t)limited_sources
-            <= (uint64_t)rename_limit * (uint64_t)rename_limit))
+       if (st_mult(num_destinations, limited_sources)
+           <= st_mult(rename_limit, rename_limit))
                return 2;
        return 1;
 }