Portability of the C Program Language and the Unix System - Essay Example

the original c compilers could not represent the relative sizes of floating-point data and integers in a machine-independent way.
a) What architectural structures do the description of the Portable C compiler illustrate? Explain.

The structure of a mobile c compiler design was in such a way that it could be adaptable to other different machines and not only UNIX machines. The architectural structure of the portable compiler could be easily modified. The compiler contained approximately 8000 lines of code and less than 20 percent of which was machine-dependent. The maintenance work of the c compiler code is easy because the structure has a large portion of similar code in many systems like the IBM System/370. In addition Honeywell 6000, Inter-data 8/32, SEL86 or even in eclipse and DEC VAX-11/780. Its structure also consists of an intermediate file found in the interface between the passes of portable c. This file contains representations of expression trees and character illustrations of stereotyped code for epilogues and subroutine prologues.
b) What architectural structures does the description of portability of UNIX illustrate? Explain.

The structural architecture of a portable UNIX was created from the realization that the operating systems of many machines had hardware architectures that were a significant problem to the implementation of the UNIX system. The structure was to have a c compiler that could be altered without many problems and create new code for various machines. The c language was to be extended to allow many c programs to become portable to a larger range of devices and be able to identify constructions that are non-portable. It illustrates the structure of re-coding a language in this case the c language as this would allow detection of machine dependencies and isolate them. It would also enable demonstration of portability by using it in other machines.

c) Based on the paper, what were the compromises or trade-offs in the design of the Portable C compiler?
The portable c compiler had to compromise its optimality with heuristic algorithms so that it could be able to get efficient and acceptable code to be generated in a quite reasonable time. The creation of the portable c compiler had to create a balance between creating entirely machine-independent code and some lines of code that were machine dependent. The machine-dependent lines of code handled the first pass that handles lexical, syntax analysis, and symbol table management and generate machine-dependent code like epilogues and subroutines is made up of machine-dependent lines of code especially.

d) Based on the paper, what were the compromises or trade-offs in the design of UNIX?
The UNIX system was designed in c language which is mainly used in network programming. Therefore, in its design UNIX systems compromised ultimate portability for more efficiency. The Unix systems have been designed to strike a balance between powerful and convenient features, and this also has to consider the ease with which implementation of some features efficiently on different machines is achieved.

5.2. Write a Module Guide for the Portable C compiler.
The design of a portable c compiler has to be constituted of three modules.
• Storage allocation
• Stereotyped code sequence for switches, labels, and subroutine exit and entry points.
• Code production for expressions
5.3. Treating the Portable C compiler as a product family (Johnson and Ritchie, 1978)
I) what are the commonalities?
The c language belonged to the traditional procedural family that comprised BCPL, B, and C which were typified by both FORTRAN and Algol 60. The similarities of these languages include:

• They are system-programming languages.
• These languages can easily accommodate translations of relatively simple compilers.
• They use library routines for input and output and other interactions with operating systems.
• These languages are compactly described and are relatively small.
• Abstractions introduced by these languages are quickly grounded in the elaborate data types and operations given by conventional computers.
• These languages use library procedures to specify control structures like procedure closures and co-routines.
• These languages achieve portability between machines since their abstractions lay at a high level.
II)   what are the variabilities?
• B and C languages have no nested procedures at all while procedures can be nested in the BCPL language but cannot refer to non-static objects that have been defined in the containing systems.

• BCPL and C can recognize separate compilations except for the earlier versions of the B language.
• BCPL and C both provide a means through which text from a named file can be included, but the B language does not provide this.
• C, B, and BCPL languages differ very significantly in their syntax.
• Lexical and syntactic mechanisms of BCPL are regular and more elegant than the syntactic and lexical mechanisms of both the B and C languages.
• B and C language end their statements with semicolons.
• Most semicolons in BCPL are elided after statements that end in a line boundary, and this gives convenience. Read More