.sp 1.5i
.nr H1 3
.NH
Conformant Arrays
.nh
.LP
.sp
A fifth kind of parameter, besides the value, variable, procedure, and function
parameter, is the conformant array parameter (\fBISO 6.6.3.7\fR). This
parameter, undoubtedly the major addition to Pascal from the compiler writer's
point of view, has been implemented. With this kind of parameter, the required
bounds of the index-type of an actual parameter are not fixed, but are
restricted to a specified range of values. Two types of conformant array
parameters can be distinguished: variable conformant array parameters and
value conformant array parameters.
.sp
.NH 2
Variable conformant array parameters
.LP
.sp
The treatment of variable conformant array parameters is comparable with the
normal variable parameter.
Both have in common that the parameter mechanism used is \fIcall by
reference\fR.
.br
An example is:
.br
.in +5m
to sort variable length arrays of integers, the following Pascal procedure could be used:

.nf
\fBprocedure\fR bubblesort(\fBvar\fR A : \fBarray\fR[low..high : integer] \fBof\fR integer);
\fBvar\fR i, j : integer;
\fBbegin
        for\fR j := high - 1 \fBdownto\fR low \fBdo
                for\fR i := low \fBto\fR j \fBdo
                        if\fR A[i+1] < A[i] \fBthen\fI interchange A[i] and A[i+1]
\fBend\fR;
.fi
.in -5m

For every actual parameter, the base address of the array is pushed on the
stack and for every index-type-specification, exactly one array descriptor
is pushed.
.sp
.NH 2
Value conformant array parameters
.LP
.sp
The treatment of value conformant array parameters is more complex than its
variable counterpart.
.br
An example is:
.br
.in +5m
an unpacked array of characters could be printed as a string with the following program part:

.nf
\fBprocedure\fR WriteAsString( A : \fBarray\fR[low..high : integer] \fBof\fR char);
\fBvar\fR i : integer;
\fBbegin
        for\fR i := low \fBto\fR high \fBdo\fR write(A[i]);
\fBend\fR;
.fi
.in -5m

The calling procedure pushes the base address of the actual parameter and
the array descriptors belonging to it on the stack. Subsequently the procedure
using the conformant array parameter is called. Because it is a \fIcall by
value\fR, the called procedure has to create a copy of the actual parameter.
This implies that the calling procedure knows how much space on the stack
must be reserved for the parameters. If the actual-parameter is a conformant
array, the called procedure keeps track of the size of the activation record.
Hence the restrictions on the use of value conformant array parameters, as
specified in \fBISO 6.6.3.7.2\fR, are dropped.

A description of the EM code generated by the compiler is:

.nf
.ft I
load the stack adjustment sofar
load base address of array parameter
compute the size in bytes of the array
add this size to the stack adjustment
copy the array
remember the new address of the array
.ft R
.fi