CP/M/CPM_CDROM.iso/simtel/sigm/vols200/vol200/z3lib2.hlp

Text File | 1994-07-13 | 6KB | 201 lines

Introduction   ZCPR3 Flow Control
End IF         
IFEND
Raise IF       
IFT/IFF
Test IF        
IFTEST
Toggle IF      
IFELSE
:Introduction to ZCPR3 Flow Control

Basic Defintion of Flow Control:

     Al∞ commanΣ sequence≤ issued unde≥ ZCPR│ caε bσ though⌠ ì
t∩á executσá withiεá ß TRU┼ flo≈ contro∞á state«á  Tha⌠á is¼ ì
wheneve≥á ß commanΣ i≤ executeΣ unde≥ ZCPR3¼á thσá statσá oµ ì
flo≈ contro∞ i≤ TRUE«  Iµ thσ statσ oµ flo≈ contro∞ i≤ FALS┼ ì
theε n∩ command≤ excep⌠ flo≈ command≤ wil∞ bσ executeΣ unti∞ ì
the state of flow control becomes TRUE.

Background:

     Wheε ZCPR│ firs⌠ come≤ up¼ thσ statσ oµ flo≈ contro∞ i≤ ì
alway≤á TRUE«á  An∙ commanΣ issueΣ wil∞ bσ executed«á  Iµá ß ì
Flo≈áá CommanΣá Packagσá i≤á installeΣá whicΦá support≤á thσ ì
IF/ELSE/F╔ (EnΣ IF⌐ commands¼ theε thσ statσ oµ flo≈ contro∞ ì
caε bσ changeΣ b∙ use≥ commands«  Fo≥ example¼ thσ followinτ ì
terminal session illustrates:


SCR>; any command will execute now
SCR>era *.bak
No Files
SCR>dir
MYFILE  .TXT  |  OBJECT  .BIN
SCR>; we can set a flow control state to be false
SCR>IF F
 IF F
SCR>; no command will execute now
SCR>dir
SCR>else
 IF T
SCR>dir
MYFILE  .TXT  |  OBJECT  .BIN
SCR>FI
 No IF
SCR>


     Hence¼áá wheεá an∙á commanΣá i≤á executed¼á beforσá thσ ì
executioεá actuall∙ begins¼á ZCPR│ wil∞ looδ t∩ seσá iµá thσ ì
statσ oµ thσ flo≈ contro∞ i≤ TRUE«  SucΦ i≤ thσ casσ wheε wσ ì
arσá no⌠ withiε aε I╞ conditioε o≥ wheε wσ arσ withiε onσ o≥ ì
more IF conditions, all of which are TRUE.

     ZCPR│ allow≤ thσ use≥ t∩ bσ nesteΣ int∩ IF≤ u≡ t∩ eigh⌠ ì
(8⌐á level≤ deep«á  Tha⌠ is¼á thσ structurσ oµá hi≤á commanΣ ì
sequence≤á caε takσ thσ forφ oµ somethinτ likσ thσ followinτ ì
which can be nested into 8 levels of IFs:


<set of commands>
IF T
     <set of commands>
     IF T
          <set of commands>
          IF T
               <set of commands>
          FI
          <set of commands>
     ELSE
          <set of non-executed commands>
          IF T
               <set of non-executed commands>
          FI
     FI
ELSE
     <set of non-executed commands>
FI


     CommanΣá structure≤ likσ thosσ presenteΣ abovσ arσá no≈ ì
possiblσ unde≥ ZCPR3«á  Essentially¼á ZCPR│ command≤ caε no≈ ì
take the form of a programming language in their own right.

     Thσ se⌠ oµ routine≤ availablσ iε thi≤ par⌠ oµ Z3LI┬ arσ ì
useΣ t∩ providσ thσ programme≥ ß simplσ interfacσ t∩ contro∞ ì
thσ flo≈ contro∞ withiε (anΣ outside⌐ hi≤ program«á  Hσ can¼ ì
unde≥ hi≤ owε control¼á issuσ command≤ t∩:

     « ente≥ thσ nex⌠ I╞ leve∞ iε ß TRU┼ o≥ FALS┼ condition,
     . toggle the state of the current IF level,
     . drop down to the previous IF level,
     . determine the current IF level number,
     . or multiples of the above


:End IF Level


Z3LIB Routine: IFEND


Function:
     Dro≡á t∩á thσá previou≤ I╞ level«á  Iµ thσá prograφá i≤ ì
currentl∙ withiε onσ o≥ morσ IFs¼á IFEN─ wil∞ dro≡ i⌠ t∩ thσ ì
next IF level down, terminating the current IF level.

     Naturally¼á fo≥ ß transien⌠ t∩ bσ executinτ now¼á therσ ì
i≤á currentl∙á eithe≥ n∩ I╞ leve∞ o≥ therσ i≤á ßá TRU┼á flo≈ ì
contro∞á statσ (al∞ preceedinτ IF≤ arσ TRUE)«á  Iµ wσ arσ a⌠ ì
somσá I╞ level¼á callinτ IFEN─ drop≤ u≤ int∩ thσá preceedinτ ì
one.


Inputs: None


Outputs: A=0 and Zero Flag Set (Z) if no IF level
          A=0FFH and NZ if IFEND is successful



Registers Affected: PSW


Side Effects: None


Special Error Conditions: None

:Raise IF


Z3LIB Routine: IFT/IFF


Function:
     Raisσ thσ flo≈ contro∞ statσ int∩ thσ nex⌠ leve∞ oµ IF«  ì
IF╘á raise≤á thσ statσ int∩ thσ nex⌠ leve∞ anΣá set≤á i⌠á t∩ ì
TRUE¼á whilσá IF╞á raise≤ thσ statσ int∩ thσ nex⌠ leve∞á anΣ ì
sets it to FALSE.

     Thσ flo≈ contro∞ statσ caε suppor⌠ eigh⌠ (8⌐ level≤á oµ ì
IFs¼á anΣá IF╘á anΣ IF╞ returε erro≥ code≤ indicatinτ iµá aε ì
overflo≈á (anΣ subsequen⌠ failurσ t∩ ente≥ thσá nex⌠á state⌐ ì
occurred.


Inputs: None


Outputs: A=0 and Zero Flag Set (Z) if IF level overflow
          A=0FFH and NZ if IF level OK



Registers Affected: PSW


Side Effects: None


Special Error Conditions: None

:Test IF


Z3LIB Routine: IFTEST


Function:
     T∩á determinσ thσ curren⌠ I╞ level«á  IFTES╘ return≤á ß ì
valuσ froφ ░ t∩ ╕ iε thσ ┴ register¼á indicatinτ thσ curren⌠ ì
I╞ level«  Iµ A=0¼ therσ i≤ n∩ curren⌠ IF«  Thσ Zer∩ Flaτ i≤ ì
set accordingly, so the following can be done:

          ext  IFTEST
          ...
          call iftest    ;get IF level
          jz   noif      ;process if not any IF level
          cpi  8         ;test for max IF level
          jz   atmax     ;process if at max IF level
          ...


Inputs: None



Outputs: A = number of current IF level, Zero Flag set
               accordingly


Registers Affected: PSW


Side Effects: None


Special Error Conditions: None

:Toggle IF


Z3LIB Routine: IFELSE


Function:
     Togglσá thσá TRUE/FALS┼ statσ oµ thσ curren⌠ I╞á level«  ì
I╞ thσ prograφ i≤ currentl∙ withiε aε I╞ leve∞ (theε i⌠ MUS╘ ì
bσ withiε ß TRU┼ I╞ level)¼ callinτ IFELS┼ (aε odΣ numbe≥ oµ ì
times⌐ toggle≤ thσ I╞ leve∞ t∩ FALSE«á  Tw∩ call≤ t∩á IFELS┼ ì
(an∙á eveε numbe≥ oµ calls⌐ resul⌠ iε thσ I╞ leve∞ remaininτ ì
a⌠ TRUE.


Inputs: None


Outputs: A=0 and Zero Flag Set (Z) if no current IF
          A=0FFH and NZ if successful



Registers Affected: PSW


Side Effects: None


Special Error Conditions: None