Bug#48370: Absolutely wrong calculations with GROUP BY and decimal fields when using IF

Bug#45261: Crash, stored procedure + decimal

Revert fix for Bug#45261 due to unforeseen bugs.

sql/my_decimal.h

@@ -48,12 +48,10 @@ C_MODE_END
   digits * number of decimal digits in one our big digit - number of decimal
   digits in one our big digit decreased by 1 (because we always put decimal
   point on the border of our big digits))
-
-  This value is 65 due to historical reasons partly due to it being used
-  as the maximum allowed precision and not the actual maximum precision.
 */
 #define DECIMAL_MAX_PRECISION (DECIMAL_MAX_POSSIBLE_PRECISION - 8*2)
 #define DECIMAL_MAX_SCALE 30
+#define DECIMAL_NOT_SPECIFIED 31
 
 /**
   maximum length of string representation (number of maximum decimal
@@ -77,6 +75,12 @@ inline uint my_decimal_size(uint precision, uint scale)
 }
 
 
+inline int my_decimal_int_part(uint precision, uint decimals)
+{
+  return precision - ((decimals == DECIMAL_NOT_SPECIFIED) ? 0 : decimals);
+}
+
+
 /**
   my_decimal class limits 'decimal_t' type to what we need in MySQL.
 
@@ -180,7 +184,7 @@ inline uint my_decimal_length_to_precision(uint length, uint scale,
 }
 
 inline uint32 my_decimal_precision_to_length_no_truncation(uint precision,
-                                                           uint scale,
+                                                           uint8 scale,
                                                            bool unsigned_flag)
 {
   /*
@@ -192,7 +196,7 @@ inline uint32 my_decimal_precision_to_length_no_truncation(uint precision,
                   (unsigned_flag || !precision ? 0 : 1));
 }
 
-inline uint32 my_decimal_precision_to_length(uint precision, uint scale,
+inline uint32 my_decimal_precision_to_length(uint precision, uint8 scale,
                                              bool unsigned_flag)
 {
   /*