Commit 51408489 authored by unknown's avatar unknown
Browse files

Fix for BUG#8576 

The problem was in different representations of double variables depending on
platform/compiler/compile options. In some cases double variables are represented by
64 bits (while in memory), or by 80 bits (while in FPU register). As a result equal
values are not considered "==". As many sources point out,  doubles should not be
compared by '==' for this reason. This fix subtracts the scaled minimal double
value X such that 1 + X != 1, to ensure that the inequality holds in any case.


sql/opt_range.cc:
  Do not compare double values with == because they may have different representations.
parent 17cca96e

sql/opt_range.cc

+6 −2
Original line number Diff line number Diff line
@@ -7027,8 +7027,12 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree) 
                       cur_group_key_parts, tree, cur_index_tree,

                       cur_quick_prefix_records, have_min, have_max,

                       &cur_read_cost, &cur_records);



    if (cur_read_cost < best_read_cost)

    /*

      If cur_read_cost is lower than best_read_cost use cur_index.

      Do not compare doubles directly because they may have different

      representations (64 vs. 80 bits).

    */

    if (cur_read_cost < best_read_cost - (DBL_EPSILON * cur_read_cost))

    {

      index_info= cur_index_info;

      index= cur_index;