bk commit into 4.1 tree (gkodinov:1.2465) BUG#19200

[kgeorge]

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ChangeSet
  1.2465 06/04/28 16:08:47 gkodinov@stripped +1 -0
  Bug #19200: SELECT ... WHERE with decimal condition give wrong result
  
  It is not a good idea to compare IEEE double approximate values directly.
  While some compilers handle the comparison (apparently) correctly,
  others don't. So care should be taken and the DBL_EPSILON constant be used.
  The specific case uses 2* because each of the compared numbers may lie on
  the opposite end of the (-DBL_EPSILON,DBL_EPSILON) that surrounds the number.
  Unfortunately it's not trivial to devise a test case because there's
  different rounding that takes place during different conversions.

  sql/item_cmpfunc.cc
    1.208 06/04/28 16:08:43 gkodinov@stripped +3 -3
    The updated real comparator

# This is a BitKeeper patch.  What follows are the unified diffs for the
# set of deltas contained in the patch.  The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User:	gkodinov
# Host:	rakia.progem.bg
# Root:	/home/kgeorge/mysql/4.1/B19200

--- 1.207/sql/item_cmpfunc.cc	2006-04-21 09:47:53 +03:00
+++ 1.208/sql/item_cmpfunc.cc	2006-04-28 16:08:43 +03:00
@@ -422,9 +422,9 @@
     if (!(*b)->null_value)
     {
       owner->null_value= 0;
-      if (val1 < val2)	return -1;
-      if (val1 == val2) return 0;
-      return 1;
+      if (val1 - val2 > 2 * DBL_EPSILON) return 1;
+      if (val2 - val1 > 2 * DBL_EPSILON) return -1;
+      return 0;
     }
   }
   owner->null_value= 1;