Decimal representation for optional mantissa with non-constant exponent #62

Author: donmendelson

v2-0-RC1/doc/02FieldEncoding.md

@@ -323,8 +323,10 @@ The default data ranges and null indicator are listed below for each
 decimal encoding.
 
 A message schema may optionally specify a more restricted range of valid
-values for a field. For optional fields, a special mantissa value is
-used to indicate that a field value is null.
+values for a field. 
+
+For all optional decimal fields, a special mantissa value is
+used to indicate that a field value is null. For floating-point decimals, the exponent should also be set to its null indicator.
 
 | Schema attribute  | decimal                                   | decimal64                                 | decimal32                                 |
 |------------------|------------------------------------------:|------------------------------------------:|------------------------------------------:|
@@ -397,6 +399,10 @@ Wire format of decimal 123.45 with 2 significant decimal places.
 
 `3930000000000000fe`
 
+Wire format of null floating-point decimal.
+
+`ffffffffffffffffff`
+
 Wire format of decimal64 123.45 with 2 significant decimal places.
 Schema attribute exponent = -2