MDEV-10138 Support for decimals up to 38 digits

Decimals with float, double and decimal now works the following way:

- DECIMAL_NOT_SPECIFIED is used when declaring DECIMALS without a firm number
  of decimals.  It's only used in asserts and my_decimal_int_part.
- FLOATING_POINT_DECIMALS (31) is used to mark that a FLOAT or DOUBLE
  was defined without decimals. This is regarded as a floating point value.
- Max decimals allowed for FLOAT and DOUBLE is FLOATING_POINT_DECIMALS-1
- Clients assumes that float and double with decimals >= NOT_FIXED_DEC are
  floating point values (no decimals)
- In the .frm decimals=FLOATING_POINT_DECIMALS are used to define
  floating point for float and double (31, like before)

To ensure compatibility with old clients we do:

- When storing float and double, we change NOT_FIXED_DEC to
  FLOATING_POINT_DECIMALS.
- When creating fields from .frm we change for float and double
  FLOATING_POINT_DEC to NOT_FIXED_DEC
- When sending definition for a float/decimal field without decimals
  to the client as part of a result set we convert NOT_FIXED_DEC to
  FLOATING_POINT_DECIMALS.
- variance() and std() has changed to limit the decimals to
  FLOATING_POINT_DECIMALS -1 to not get the double converted floating point.
  (This was to preserve compatiblity)
- FLOAT and DOUBLE still have 30 as max number of decimals.

Bugs fixed:

variance() printed more decimals than we support for double values.

New behaviour:
- Strings now have 38 decimals instead of 30 when converted to decimal
- CREATE ... SELECT with a decimal with > 30 decimals will create a column
  with a smaller range than before as we are trying to preserve the number of
  decimals.


Other changes
- We are now using the obsolete bit FIELDFLAG_LEFT_FULLSCREEN to specify
  decimals > 31
- NOT_FIXED_DEC is now declared in one place
- For clients, NOT_FIXED_DEC is always 31 (to ensure compatibility).
  On the server NOT_FIXED_DEC is DECIMAL_NOT_SPECIFIED (39)
- AUTO_SEC_PART_DIGITS is taken from DECIMAL_NOT_SPECIFIED
- DOUBLE conversion functions are now using DECIMAL_NOT_SPECIFIED instead of
  NOT_FIXED_DEC

2 files changed, 4 insertions, 5 deletions

diff --git a/strings/dtoa.c b/strings/dtoa.c
index c3ab347f94c..fdf7bceddfd 100644
--- a/strings/dtoa.c
+++ b/strings/dtoa.c
@@ -90,7 +90,7 @@ size_t my_fcvt(double x, int precision, char *to, my_bool *error)
   int decpt, sign, len, i;
   char *res, *src, *end, *dst= to;
   char buf[DTOA_BUFF_SIZE];
-  DBUG_ASSERT(precision >= 0 && precision < NOT_FIXED_DEC && to != NULL);
+  DBUG_ASSERT(precision >= 0 && precision < DECIMAL_NOT_SPECIFIED && to != NULL);
   
   res= dtoa(x, 5, precision, &decpt, &sign, &end, buf, sizeof(buf));
 
diff --git a/strings/my_vsnprintf.c b/strings/my_vsnprintf.c
index 75514a90925..3cc7a4e7ea8 100644
--- a/strings/my_vsnprintf.c
+++ b/strings/my_vsnprintf.c
@@ -16,11 +16,10 @@
 
 #include "strings_def.h"
 #include <m_ctype.h>
-#include <stdarg.h>
 #include <my_sys.h>
 #include <my_base.h>
 #include <my_handler_errors.h>
-
+#include <mysql_com.h>                        /* For FLOATING_POINT_DECIMALS */
 
 #define MAX_ARGS 32                           /* max positional args count*/
 #define MAX_PRINT_INFO 32                     /* max print position count */
@@ -240,8 +239,8 @@ static char *process_dbl_arg(char *to, char *end, size_t width,
 {
   if (width == MAX_WIDTH)
     width= FLT_DIG; /* width not set, use default */
-  else if (width >= NOT_FIXED_DEC)
-    width= NOT_FIXED_DEC - 1; /* max.precision for my_fcvt() */
+  else if (width >= FLOATING_POINT_DECIMALS)
+    width= FLOATING_POINT_DECIMALS - 1; /* max.precision for my_fcvt() */
   width= MY_MIN(width, (size_t)(end-to) - 1);
   
   if (arg_type == 'f')