less strict assert to take into account weird cases

mysql-test/r/type_float.result

@@ -114,6 +114,9 @@ select min(a) from t1;
 min(a)
 -0.010
 drop table t1;
+create table t1 (c20 char);
+insert into t1 (c20) values (5000.0);
+drop table t1;
 create table t1 (f float(54));
 Incorrect column specifier for column 'f'
 drop table if exists t1;

mysql-test/t/type_float.test

@@ -54,6 +54,13 @@ select a from t1 order by a;
 select min(a) from t1;
 drop table t1;
 
+#
+# float in a char(1) field
+#
+create table t1 (c20 char);
+insert into t1 (c20) values (5000.0);
+drop table t1;
+
 # Errors
 
 --error 1063

sql/field.cc

@@ -3733,15 +3733,17 @@ static void store_double_in_string_field(Field_str *field, uint32 field_length,
     use_scientific_notation= (field->ceiling < nr);
   }
   length= (uint)sprintf(buff, "%-.*g",
-                        use_scientific_notation ? max(0,field_length-5) : field_length,
+                        use_scientific_notation ? max(0,(int)field_length-5) : field_length,
                         nr);
   /*
     +1 below is because "precision" in %g above means the
     max. number of significant digits, not the output width.
     Thus the width can be larger than number of significant digits by 1
     (for decimal point)
+    the test for field_length < 5 is for extreme cases,
+    like inserting 500.0 in char(1)
   */
-  DBUG_ASSERT(length <= field_length+1);
+  DBUG_ASSERT(field_length < 5 || length <= field_length+1);
   field->store(buff, min(length, field_length));
 }