TOOLS FOR STRUCTURED PROGRAMMING






Structured programming is  both  a  philosophy  and  a  methodology  for
program and system design.  As a philosophy, it requires effort to grasp
the concepts, and practice to fully comprehend its capabilities.   As  a
methology,  it  is  a  classic candidate for the development of software
tools.


Such a tool is now available for macro on the PDP-11 series.
 
	* A Structured Macro library for the PDP11.
 
 
 





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STRUCTURED MACROS FOR THE PDP11


A library of macros is available for the PDP-11 which allow the user  to
write  well  structured  control  constructs.  These constructs take the
place of all  branch  instructions  and  local  labels,  and  most  loop
counters  and  test  instructions.  They provide a more readable form of
code, and greatly assist program understandability.  The macro  file  is
available as:
 
	LB:[1,1] PDPSML.MLB
 
PDPSML was released several years ago, and has been used extensively.


In the description below, brackets (< >) are  used  to  denote  optional
parameters.

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$$$SML


The following macro initializes the use of the structured macro library.
 
		.LIBRARY /sys$library:pdpsml/
 
		.MCALL $$SML
		$$SML

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FOR - ENDF - FEXIT


The following macros provide the construct of a counting loop.
 
	FOR	VAR,FROM,TO<,BY<,SIGN<,JMP>>>
 
	  Code to be executed in the loop.
 
	ENDF	<JMP>


where:


        VAR     is the loop index.

        FROM    is the starting value for index.

        TO      is the last value for which the the loop is executed.

        BY      is the increment, which defaults to 1.

        SIGN    (-) indicates decrementing of the loop.  (Must  be  used
                in addition to negative value of BY.)

        JMP     forces long jumps to be used.

NOTE:   INDEX VARIABLE IS NOT GUARANTEED TO BE A  SPECIFIC  VALUE  AFTER
        FALLING THROUGH THE LOOP.

FEXIT   is used to prematurely exit from a FOR loop;  however,  its  use
        is discouraged.



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DOCASE - CASE - ENDC


The following macros are used  to  provide  a  multiple-valued  decision
structure.
 
	DOCASE ARG
 
	   CASE<B>	<VAL1<,VAL2<,JMP<,JMPI>>>>
 
	        Code for case true.
 
	   CASE<B>	<VAL1<,VAL2<,JMP<,JMPI>>>>
 
	        Code for case true.
 
	ENDC
 
where:


        B       is present for byte mode.

        ARG     is the decision index, which must  not  be  an  external
                reference.

        VAL1    is the lower limit for which the block is executed.

        VAL2    is the upper limit for  which  the  block  is  executed,
                defaulting to VAL1.

        JMP     forces a long jump to be used for exit of a case.

        JMPI    forces a long jump to be used to get to  the  next  case
                statement.

NOTE:   Only one case is executed, the first one for which the ARG falls
        within the bounds.

        If both VAL1 and VAL2 are missing, the always case is generated.



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IF - ELSE - ENDI


The following macros provide the TRUE/FALSE conditional construct.
 
	IF<B>	CONDITION<,JMP>
 
	   Code to be executed if condition
	   satisfied.
 
	ELSE	<JMP>
 
	   Code to be executed if condition
	   not satisfied.
 
	ENDI
 
where:


        B               is present for byte mode.

        CONDITION:=     LOGICAL
                        X,RELATION,Y
                        ,STATUS

        Logical:=       Logical variable (nonzero-TRUE, zero-FALSE)

        X:=             Variable

        Y:=             Variable
 
	RELATION:=	EQ,NE,LT,LE,GT,GE,LO,LOS,HI,HIS,SET,
			CLEAR
 
	STATUS:=	CC,CS,VC,VS,EQ,NE,LT,GT,GE,LO,LOS,HI,
			HIS,PL,MI,CARRY
 

        JMP             forces long jump to be used.



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UNTIL - ENDU - UEXIT


The following macros proviie the loop construct with conditional testing
at the bottom.
 
	UNTIL<B>	CONDITION<,JMP>
 
	  Code to be executed while condition is
	  not satisfied.
 
        ENDU    <JMP>
 
where:


        B               is present for byte mode.

        CONDITION:=     LOGICAL
                        X,RELATION,Y
                        ,STATUS

        Logical:=       Logical variable (nonzero-TRUE, zero-FALSE)

        X:=             Variable

        Y:=             Variable
 
	RELATION:=	EQ,NE,LT,LE,GT,GE,LO,LOS,HI,HIS,SET,
			CLEAR
 
	STATUS:=	CC,CS,VC,VS,EQ,NE,LT,GT,GE,LO,LOS,HI,
			HIS,PL,MI,CARRY
 

        JMP             forces long jumps to be used.


NOTE:   The UNTIL loop is always executed at least once.

UEXIT   is used to prematurely exit from an UNTIL  loop;   however,  its
        use is discouraged.



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WHILE - ENDW - WEXIT


The following macros provide the loop construct with conditional testing
at the top.
 
	WHILE<B>	CONDITION<,JMP>
 
	  Code to be executed while condition is
	  satisfied.
 
        ENDW    <JMP>
 
where:


        B               is present for byte mode.

        CONDITION:=     LOGICAL
                        X,RELATION,Y
                        ,STATUS

        Logical:=       Logical variable (nonzero-TRUE, zero-FALSE)

        X:=             Variable

        Y:=             Variable
 
	RELATION:=	EQ,NE,LT,LE,GT,GE,LO,LOS,HI,HIS,SET,
			CLEAR
 
	STATUS:=	CC,CS,VC,VS,EQ,NE,LT,GT,GE,LO,LOS,HI,
			HIS,PL,MI,CARRY
 

        JMP             forces long jump to be used.


NOTE:   The WHILE loop is never executed if the condition is false.

WEXIT   is used to prematurely exit from an WHILE  loop;   however,  its
        use is discouraged.