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Fix for BUG#8576

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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.
This commit is contained in:
timour@mysql.com
2005-02-23 13:39:29 +02:00
parent 82571d6b84
commit a6bf8c6686
1 changed files with 6 additions and 2 deletions
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8
sql/opt_range.cc
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@ -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;