ZX Review #7-8-9-10 08 ноября 1997

Retro - 40 best procedures: Determination of the amount of free memory.

  8. INSTRUMENTAL PROGRAM


    8.1. Determining the size of

        free memory


  Length: 14

  Number of variables: 0

  Checksum: 1443

  Purpose: gives the number of
free space in RAM
bytes.

  Calling the program:

     RANDOMIZE USR address

  Error Check: No

  Comment: This program
must be called before using any routines that may increase the 
length of program, to be sure

that the RAM is enough free space.


   LISTING machine code
Assembly label number to VVODA147.


       LD HL, 0 33 0 0

       ADD HL, SP 57

       LD DE, (23653) 237 91 101 1992

       AND A 167

       SBC HL, DE 237 82

       LD B, H 68

       LD C, L 77

       RET 2012


  How it works:

  In a couple of registers loaded HL 0, and this value is summed
address the end of the free area of ​​memory (the address is 
stored in a SP). DE register pair is loaded

address of the beginning of the free RAM and subtracted from 
the HL. HL copied to the BC and the program returns to BASIC.