Pl1 programming language pdf

It then asks from the user to enter the text to encrypt or decrypt and calls the relative internal procedures functions to perform the selected action.

The output of the action is presented to the user and the program terminates. Encrypt procedure: This is the function responsible for the encryption of data. Free Ebook Breakers Book 1.

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All internal static data is initialized as its storage is allocated. Due to the dynamic linking and loading characteristics of the Multics environment, the allocation and initialization of external static storage is rather unusual. The compiler creates a special type of link which causes the linker module of the operating system to create and initialize the external data upon first reference.

Therefore, if two programs contain references to the same item of external data, the first one to reference that data will allocate and initialize it.

The code generator scans the internal representation transforming it into machine instructions which it outputs into the text segment. During this scan the code generator allocates storage for temporaries, and maintains a history of the contents of index registers to prevent excessive loading and storing of index values.

Code generation consists of three distinct activities: address computation, operator selection and macro expansion. Address computation is the process of transforming the offset expressions of a reference node into a machine address or an instruction sequence which leads to a machine address. Operator selection is the translation of operators into n-operand macros which reflect the properties of the machine.

A one-to-one relationship often exists between the macros and instructions but many operations load long string, etc. All macros are expanded in actual code by the macro expander which uses a code pattern table macro skeletons to select the specific instruction sequences for each macro.

The length of the object program is minimized by the extensive use of out-of-line code sequences. Although the compiled code makes heavy use of out-of-line code sequences, the compiled code is not in any respect interpretive.

The object code produce for each operator is very highly tailored to the specific attributes of that operator. All out-of-line sequences are contained in a single "operator" segment which is shared by all users. The in-line code reaches on out-of-line sequence through transfer instructions, rather than through the standard subroutine mechanism. We believe that the time overhead associated with the transfers is more than redeemed by the reduction in the number of page faults caused by shorter object programs.

System performance is improved by insuring that the pages of the operator segment are always retained in storage. Each task Multics process has its own stack which is extended pushed upon entry to block and is reverted popped upon return from a block. Prior to the execution of each statement it is extended to create sufficient space for any variable length string temporaries used in that statement. Constant size temporaries are allocated at compile time and do not cause the stack to be extended for each statement.

The term prologue describes the computations which are performed after block entry and prior to the execution of the first source statement. These actions include the establishment of the condition prefix, the computation of the size of variable size automatic data, extension of the stack to allocate automatic data, and the initialization of automatic data.

Epilogues are not needed because all actions which must be undone upon exit from the block are accomplished by popping the stack. The stack is popped for each return or non-local go to statement. If the address of the data is constant, it is computed at compile time. If it is a mixture of constant and variable terms, the constant terms are combined at compile time. Descriptors are never used to address or allocate data. All string operations are done by in-line code or by "transfer" type subroutinized code.

No descriptors or calls are produced for string operations. The SUBSTR built-in function is implemented as apart of the normal addressing code and is therefore as efficient as a subscripted array reference.

A string temporary or dummy is designed in such a way that it appears to be both a varying and non-varying string. This means that the programmer does not need to be concerned with whether a string expression is varying or non-varying when he uses such an expression as an argument. The integer is used to hold the current size of the string in bits or characters. Using this data format, operations on vayring strings are just as efficient as operations on non-vayring strings. The design of the condition machinery minimizes the overhead associated with enabling and reverting on-units and transfers most of the cost to the signal statement.

All data associated with on-conditions, including the condition prefix, is allocated in the stack. The normal popping of the stack reverts all enabled on-units and restores the proper condition prefix. Stack storage associated with each block is threaded backward to the previous block. The signal statement uses this thread to search back through the stack looking for the first enabled unit for the condition being signaled.

Figure 7 shows the organization of enabled on-units in the stack. In these cases, the missing size information is assumed to be supplied by the argument which corresponds to the parameter. This missing size information is not explicitly supplied by the programmer as is the case in Fortran, rather it must be supplied by the compiler as indicated in the following example:. Since parameter A assumes the length of the argument B, the compiler must include the length of B in the argument list of the call to SUB.

The declaration of an entry name may or may not include a description of the arguments required by that entry. If such a description is not supplied, then the calling program must assume that argument descriptors are needed, and must include them in all cans to the entry.

If a complete argument description is contained in the calling program, the compiler can determine if descriptors are needed for calls to the entry. In the previous example the entry SUB was not fully declared and the compiler was forced to assume that an argument descriptor for B was required.

Since descriptors are often created by the calling procedure but not used by the called procedure, it is desirable to separate them from the argument information which is always used by the called procedure.

Since descriptors contain no addressing information, they are quite often constant and can be prepared at compile time. Mills was responsible for the design and implementation of the syntactic analyzer and the Multics system interface, B.

Wolman designed and built the code generator and operator segment, and G. Chang implemented the semantic translator. Valuable advice and ideas were provided by A. The earlier work of M.

Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. Figure 1-The internal representation of a program. The example is greatly simplified. Only the statements of procedure F are shown in detail.

Figure 6-The internal representation of a statement before and after the execution of the search function. The broken lines show the statement's operands before the search. Procedure A enabled an on-unit for condition X and called procedure B. Health Care Skills. Finance Skills. All Courses. All Practice Tests.

Question 1. Go programming language Tutorial Question Go programming language Interview Questions Question Disconnect from the data server : To prepare the program for execution, you follow one of these procedures: Preprocess, precompile, compile, link, and bind the program.

Preprocess, then compile the program with the SQL option, and then link and bind the program. F Sharp programming language Tutorial Question Data types include: Real or complex, floating-point or fixed-point, signed or unsigned binary or decimal, and numeric and editable picture data with programmer selected precision. Varying or nonvarying, character or bit or graphic, run-time adjustable or compile-time fixed length strings. Program control data supporting pointer and offset locators, adjustable or fixed size areas for grouping of dynamic allocations, entry data "function pointers" , and file, label, and format data.

Groovy programming language Interview Questions Question D Programming Language Tutorial Question F Sharp programming language Interview Questions Question For all storage classes, data may be automatically initialized when it is allocated. These functions cover: Character, Bit, and Graphic string manipulation e. Clipper programming language Interview Questions Question Answer : Conditions can be enabled in a variety of ways to have your program automatically diagnosed for Array subscripts being out of range.

String and substrings being out of range. Data exceeding declared or machine supported precisions. D Programming Language Interview Questions.

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