ZX Review #7-8-9-10 08 ноября 1997

Retro - 40 best procedures: Exchange token.

       7.2. Exchanging tokens


   Note: a "token"
means any keyword
call (command, function) of
"Dictionary" BASIC, which is considered by the program
(Both computer and interpreter) in the form of some code.

  Length: 46

  Number of variables: 2

  Checksum: 5000

  Purpose: The change any occurrence of a given token in a 
BASIC program on another token (For example, all operators PRINT

may be changed at LPRINT).

  Variables:

     Name: chr old

     Length: 1

     Cell: 23296

     Comment: The code replaces the token.

     Name: chr new

     Length: 1

     Cell: 23297

     Comment: The code is a replacement token.

  Calling the program:

     RANDOMIZE USR address

  Error checking: If BEYSIKprogrammy not in memory or a
of the two specified tokens has
code is less than 32, then the procedure returns to BASIC.

  Comment: This procedure
very quickly, but the longer
BASIC program, the slower
it works.


   LISTING machine code
Assembly label number to VVODA147.


       LD BC, (23296) 237 75 0 91

       LD A, 31 62 31

       CP B 184

       RET NC 208

       CP C 185

       RET NC 208

       LD HL, (23635) 42 83 92
NXT_CH INC HL 35

       INC HL 35

       INC HL 35
CHECK LD DE, (23,627) two hundred thirty-seven 91 75 92

       AND A 167

       SBC HL, DE 237 82

       RET NC 208

       ADD HL, DE 25

       INC HL 35

       LD A, (HL) 126

       INC HL 35

       CP 13254 1913

       JR Z, NXT_CH 40237

       CP 14254 1914

       JR NZ, COMP 32 3

       INC HL 35

       JR NEXT_CHR 24230
CONP DEC HL 1943

       CP C 185

       JR NZ, CHECK 32229

       LD (HL), B 112

       JR CHECK 24226
2

  How it works:

  In the registers B and C are loaded
old and new tokens, respectively. If any of the tokens
has a code less than 32, then
the program returns to BASIC.

  In a pair of HL recorded address of the start-BASIC program. 
A pair of registers, and then increases compared with the 
address field variables. If HL is not less

than the start address of the variables, the program returns to
BASIC.

  Pair HL is increased, pointing to the next character. Code
this character is loaded into the accumulator and HL increases
again. If the value in the accumulator is equal to 13 or 14 
(ENTER or NUMBER), routine returns to NXT_CH, and HL increased, 
pointing to the next symbol. If the battery does not contain 13 
or 14, the stored value is compared with the chr old. If a 
couple is found, this symbol replaced by chr new.


  Then return to the test
(CHECK) at the end of the processed
program.