A better CREATE ... DOES>

[TG9541]

Better means faster and smaller. The new solution size and speed is about the same as an ordinary CREATE, VARIABLE or CONSTANT:

: EMPTY CREATE DOES> ;

      EMPTY    tempty
      CREATE   tcreate 
      VARIABLE tvar

: testempty  FOR P1L tempty  P1H DROP NEXT ;
: testcreate FOR P1L tcreate P1H DROP NEXT ;
: testvar    FOR P1L tvar    P1H DROP NEXT ;

The new solution is only marginally slower than a pure CREATE and on par with VARIABLE:
10 testempty 2µs:

10 testcreate 1.4µs:

10 testvariable 1.9µs:

The measurements where done with PulseView on a STM8S001J3M3 with 16MHz HSI and code compiled to Flash ROM. The pin-debug adds 2 cycles (0.25µs) to the time.

[TG9541]

Here are new measurements: the "empty" DOES> (get address of the data stored by during a word definition) has a runtime of 1.82µs. That's actually a bit faster than VARIABLE and just 0.5µs slower than CREATE.

The old CREATE ... DOES> needs 3.85µs for the same task (i.e. twice as long as the new implementation).

The simple constant value implementation : dcons CREATE , DOES> @ ; is also just a bit slower than the literal stored by CONSTANT (the literal uses the STM8 instruction TRAP and requires 3 byte, like the CALL to the word defined through dcons).

Memory requirements:

[bytes]	old	new	diff
: empty CREATE DOES> ;	22	18	4
empty a	13	7	6
STM8S001J3 binary	4697	4662	35

The old implementation needs 4 bytes more for a "defining word" and 6 bytes more for a "defined" (the new DOES> has the same memory needs as a word defined by CREATE, CONSTANT or VARIABLE). Also the STM8 eForth binary is 35 bytes smaller than before.