From faad73550c157388ffb7b1606e3f896ed7b276ac Mon Sep 17 00:00:00 2001
From: unknown <ramil/ram@mysql.com/ramil.myoffice.izhnet.ru>
Date: Wed, 31 Jan 2007 09:51:05 +0400
Subject: fix for bug #19690: ORDER BY eliminates rows from the result

Depending on the queries we use different data processing methods
and can lose some data in case of double (and decimal in 4.1) fields.

The fix consists of two parts:
1. double comparison changed, now double a is equal to double b
if (a-b) is less than 5*0.1^(1 + max(a->decimals, b->decimals)).
For example, if a->decimals==1, b->decimals==2, a==b if (a-b)<0.005
2. if we use a temporary table, store double values there as is
to avoid any data conversion (rounding).


mysql-test/r/type_float.result:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - test result
mysql-test/t/type_float.test:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - test case
sql/field.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - use not_fixed flag instead of dec to check bounds.
sql/field.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - Field_Double::not_fixed flag introduced, which is set if dec == NOT_FIXED_DEC
      and is used in the ::store() to check bounds.
    - new constructor introduced (with not_fixed_arg parameter).
sql/init.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - fill log_01[] array with 0.1 powers.
sql/item_cmpfunc.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - compare_real_fixed() and compare_e_real_fixed() introduced,
      they consider double a == double b if a-b is less than 'precision',
      'precision' is set to 5*0.1^(1 + max(a->decimals, b->decimals)),
      for example, if a->decimals==1, b->decimals==2, 'precision' is 0.005
    - use the above functions if both arguments are fixed.
sql/item_cmpfunc.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - Arg_comparator::presision introduced.
    - Arg_comparator::compare_real_fixed(), Arg_comparator::compare_e_real_fixed() introduced.
sql/mysql_priv.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - log_01 array of 0.1 powers added.
sql/mysqld.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - log_01 array of 0.1 powers added.
sql/sql_select.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - if we create double field in a temporary table, set not_fixed flag
      (use proper constructor) to avoid data conversion
      in the Field_double::store(). Otherwise we can lose some data.
---
 sql/item_cmpfunc.cc | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

(limited to 'sql/item_cmpfunc.cc')

diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index 859b4e0ecc1..65f9b279a18 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -352,6 +352,17 @@ int Arg_comparator::set_compare_func(Item_bool_func2 *item, Item_result type)
         func= &Arg_comparator::compare_e_int_diff_signedness;
     }
   }
+  else if (type == REAL_RESULT)
+  {
+    if ((*a)->decimals < NOT_FIXED_DEC && (*b)->decimals < NOT_FIXED_DEC)
+    {
+      precision= 5 * log_01[max((*a)->decimals, (*b)->decimals)];
+      if (func == &Arg_comparator::compare_real)
+        func= &Arg_comparator::compare_real_fixed;
+      else if (func == &Arg_comparator::compare_e_real)
+        func= &Arg_comparator::compare_e_real_fixed;
+    }
+  }
   return 0;
 }
 
@@ -459,6 +470,44 @@ int Arg_comparator::compare_e_real()
   return test(val1 == val2);
 }
 
+
+int Arg_comparator::compare_real_fixed()
+{
+  /*
+    Fix yet another manifestation of Bug#2338. 'Volatile' will instruct
+    gcc to flush double values out of 80-bit Intel FPU registers before
+    performing the comparison.
+  */
+  volatile double val1, val2;
+  val1= (*a)->val();
+  if (!(*a)->null_value)
+  {
+    val2= (*b)->val();
+    if (!(*b)->null_value)
+    {
+      owner->null_value= 0;
+      if (val1 == val2 || fabs(val1 - val2) < precision)
+        return 0;
+      if (val1 < val2)
+        return -1;
+      return 1;
+    }
+  }
+  owner->null_value= 1;
+  return -1;
+}
+
+
+int Arg_comparator::compare_e_real_fixed()
+{
+  double val1= (*a)->val();
+  double val2= (*b)->val();
+  if ((*a)->null_value || (*b)->null_value)
+    return test((*a)->null_value && (*b)->null_value);
+  return test(val1 == val2 || fabs(val1 - val2) < precision);
+}
+
+
 int Arg_comparator::compare_int_signed()
 {
   longlong val1= (*a)->val_int();
-- 
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