init

encode.go

@@ -47,7 +47,8 @@ func encode(parameterStatus *parameterStatus, x interface{}, pgtypOid oid.Oid) [
 		return strconv.AppendBool(nil, v)
 	case time.Time:
 		return formatTs(v)
-
+	case decomposer:
+		// TODO: https://github.com/sfackler/rust-postgres/issues/119#issuecomment-166669557
 	default:
 		errorf("encode: unknown type for %T", v)
 	}
@@ -593,3 +594,33 @@ func (nt NullTime) Value() (driver.Value, error) {
 	}
 	return nt.Time, nil
 }
+
+// decomposer composes or decomposes a decimal value to and from individual parts.
+// There are four separate parts: a boolean negative flag, a form byte with three possible states
+// (finite=0, infinite=1, NaN=2),  a base-2 big-endian integer
+// coefficient (also known as a significand) as a []byte, and an int32 exponent.
+// These are composed into a final value as "decimal = (neg) (form=finite) coefficient * 10 ^ exponent".
+// A zero length coefficient is a zero value.
+// If the form is not finite the coefficient and scale should be ignored.
+// The negative parameter may be set to true for any form, although implementations are not required
+// to respect the negative parameter in the non-finite form.
+//
+// Implementations may choose to signal a negative zero or negative NaN, but implementations
+// that do not support these may also ignore the negative zero or negative NaN without error.
+// If an implementation does not support Infinity it may be converted into a NaN without error.
+// If a value is set that is larger then what is supported by an implementation is attempted to
+// be set, an error must be returned.
+// Implementations must return an error if a NaN or Infinity is attempted to be set while neither
+// are supported.
+type decomposer interface {
+	// Decompose returns the internal decimal state into parts.
+	// If the provided buf has sufficient capacity, buf may be returned as the coefficient with
+	// the value set and length set as appropriate.
+	Decompose(buf []byte) (form byte, negative bool, coefficient []byte, exponent int32)
+
+	// Compose sets the internal decimal value from parts. If the value cannot be
+	// represented then an error should be returned.
+	// The coefficent should not be modified. Successive calls to compose with
+	// the same arguments should result in the same decimal value.
+	Compose(form byte, negative bool, coefficient []byte, exponent int32) error
+}