Fix for bug #14268 (Bad FLOAT->DECIMAL conversion)

mysql-test/t/type_newdecimal.test

@@ -1050,3 +1050,38 @@ select cast(@non_existing_user_var/2 as DECIMAL);
 #
 --error 1427
 create table t (d decimal(0,10));
+
+#
+# Bug #14268 (bad FLOAT->DECIMAL conversion)
+#
+
+CREATE TABLE t1 (
+   my_float   FLOAT,
+   my_double  DOUBLE,
+   my_varchar VARCHAR(50),
+   my_decimal DECIMAL(65,30)
+);
+SHOW CREATE TABLE t1;
+
+let $max_power= 32;
+while ($max_power)
+{
+   eval INSERT INTO t1 SET my_float = 1.175494345e-$max_power,
+                           my_double = 1.175494345e-$max_power,
+                           my_varchar = '1.175494345e-$max_power';
+   dec $max_power;
+}
+SELECT my_float, my_double, my_varchar FROM t1;
+
+SELECT CAST(my_float   AS DECIMAL(65,30)), my_float FROM t1;
+SELECT CAST(my_double  AS DECIMAL(65,30)), my_double FROM t1;
+SELECT CAST(my_varchar AS DECIMAL(65,30)), my_varchar FROM t1;
+
+UPDATE t1 SET my_decimal = my_float;
+SELECT my_decimal, my_float   FROM t1;
+UPDATE t1 SET my_decimal = my_double;
+SELECT my_decimal, my_double  FROM t1;
+UPDATE t1 SET my_decimal = my_varchar;
+SELECT my_decimal, my_varchar FROM t1;
+
+DROP TABLE t1;

strings/decimal.c

@@ -973,7 +973,7 @@ int double2decimal(double from, decimal_t *to)
 {
   /* TODO: fix it, when we'll have dtoa */
   char s[400], *end;
-  sprintf(s, "%f", from);
+  sprintf(s, "%.16G", from);
   end= strend(s);
   return string2decimal(s, to, &end);
 }