Joseph M. Newcomer

Tactus: toolkit-level support for synchronized interactive multimedia

Tactus addresses problems of synchronizing and controlling various interactive continuous-time media. The Tactus system consists of two main parts. The first is a server that synchronizes the presentation of multiple media, including audio, video, graphics, and MIDI at a workstation. The second is a set of extensions to a graphical user interface toolkit to help compute and/or control temporal streams of information and deliver them to the Tactus Server. Temporal toolkit objects schedule computation events that generate media. Computation is scheduled in advance of real time to overcome system latency, and timestamps are used to allow accurate synchronization by the server in spite of computation and transmission delays. Tactus supports precomputing branches of media streams to minimize latency in interactive applications.

Code generation in a machine-independent compiler

This paper presents some code generation issues in the context of the PQCC Production-Quality Compiler-Compiler project [8]. The approach taken is unusual in several ways. The machine-dependent information for selection of code sequences, register assignments, etc., has been separated throughout, in tabular form, from the machine-independent algorithms. This not only greatly simplifies the development of code generators for new machines or languages, but paves the way for automatic generation of these tables from formal machine descriptions such as ISP [1]. A parse-tree-like internal program representation is used, facilitating the use of context and data dependency information about expressions. The code generation process has been broken into several phases. This leads to simplification and better understanding of the code generation process, and also allows important improvements in the quality of generated code. The algorithms for preliminary determination of addressing modes, allocation of registers and other locations, and the code selection case analysis are discussed. The algorithms described in the paper are being implemented and used in the PQCC compiler.

A Comparison of Programming Languages for Software Engineering.

Four programming languages (Fortran, Cobol, Jovial and the proposed DoD standard) are compared in the light of modern ideas of good software engineering practice. The comparison begins by identifying a core for each language that captures the essential properties of the language and the intent of the language designers. These core languages then serve as a basis for the discussion of the language philosophies and the impact of the language on gross program organization and on the use of individual statements.

Tactus: Toolkit-Level Support for Synchronized Interactive Multimedia

Tactus addresses problems of synchronizing and controlling various interactive continuous-time media. The Tactus system consists of two main parts. The first is a server that synchronizes the presentation of multiple media, including audio, video, graphics, and MIDI, at a workstation. The second is a set of extensions to a graphical user interface toolkit to help compute and/or control temporal streams of information and deliver them to the Tactus Server. Temporal toolkit objects schedule computation events that generate media. Computation is scheduled in advance of real time to overcome system latency, and timestamps are used to allow accurate synchronization by the server in spite of computation and transmission delays. Tactus supports precomputing branches of media streams to minimize latency in interactive applications.

IDL: Past Experience and New Ideas

This paper is based on the authors experience in constructing an implementation of the Interface Description Language (IDL). The result of this experience was some insights into language design, human interfaces, and system structuring, as well as methodologies for the composition of complex tools. Certain complexities of the IDL implementation are discussed in this paper, showing that quite efficient implementaions are possible. Finally, a set of interesting directions for IDL and IDL-derived systems are suggested, including programming environment and database related work.

Tools For Automatic Compiler Generation (Panel Discussion)

As various parts of the compiling process have become better understood, it has been possible to package this understanding in tools that can be used by nonspecialists. This talk describes tools for parser generation and lexical analyzer generation which are available under the UNIX% operating system. It will also touch on some less successful attempts to package understanding of symbol table management. In addition to specific tools, the UNIX system eases many of the ancillary tasks of the compiler writer: debugging, regression testing, and constructing new versions of the compiler, to name a few. The talk will draw from practical experience in the construction of a portable compiler for the language C, which has been moved to over a dozen different machines. Since the early history of compilers, researchers have attempted to systematize and automate the production of compilers. The most successful aspect of this attempt has been syntax analysis. It is now commonplace to use a table-driven syntax analyzer which is automatically constructed from a generalized context-free grammar specifying the syntax of the source language (see, for example, [1]). Such an analyzer is easily obtained or modified, provably correct, and modular. In order to automate the production of the code-generator module of a compiler, it is desirable to take a similar approach - namely, to find techniques to construct the code generator automatically from an easily specified description of the computer architecture. We would again have the advantages that the code-generator would be provably correct, modular, and easily modified to generate code for a new kind of machine. In the talk, a technique will be presented to provide an easily specified machine description to a program which computes a table of information from which another algorithm generates probably correct code. The results, described more fully in [4], [5], [6], are based in part on earlier work reported in [7] and [8]. Other current research on this topic, described in [2] and [3], will also be discussed. The PQCC (Production-Quality Compiler-Compiler) project is an effort aimed at the automatic construction of production quality, optimizing compilers. The goal, is, with no more than a few man-months effort, to produce a compiler that is competitive in every respect with the best hand-crafted compilers available today. Input to this automatic construction process is formal descriptions of the source language and target machine. PQCC differs from nearly all previous work in this area in that we are concentrating on the semantic and machine-dependent phases of compilation—as opposed to lexical and syntactic analysis. Each phase has been formalized in a manner that permits it to be expressed in table-driven form. Thus the automatic construction of the compiler consists of deriving these tables from the semantic definitions of the language and target machine. Table-driven prototypes have just been completed for most compiler phases, and work is now proceeding on improving and automating their generation. The talk will go into some detail on one of these phases, code generation, discussing the formalization of the (table-driven) algorithms and the automatic construction of the tables from a machine description.As various parts of the compiling process have become better understood, it has been possible to package this understanding in tools that can be used by nonspecialists. This talk describes tools for parser generation and lexical analyzer generation which are available under the UNIX% operating system. It will also touch on some less successful attempts to package understanding of symbol table management. In addition to specific tools, the UNIX system eases many of the ancillary tasks of the compiler writer: debugging, regression testing, and constructing new versions of the compiler, to name a few. The talk will draw from practical experience in the construction of a portable compiler for the language C, which has been moved to over a dozen different machines. Since the early history of compilers, researchers have attempted to systematize and automate the production of compilers. The most successful aspect of this attempt has been syntax analysis. It is now commonplace to use a table-driven syntax analyzer which is automatically constructed from a generalized context-free grammar specifying the syntax of the source language (see, for example, [1]). Such an analyzer is easily obtained or modified, provably correct, and modular. In order to automate the production of the code-generator module of a compiler, it is desirable to take a similar approach - namely, to find techniques to construct the code generator automatically from an easily specified description of the computer architecture. We would again have the advantages that the code-generator would be provably correct, modular, and easily modified to generate code for a new kind of machine. In the talk, a technique will be presented to provide an easily specified machine description to a program which computes a table of information from which another algorithm generates probably correct code. The results, described more fully in [4], [5], [6], are based in part on earlier work reported in [7] and [8]. Other current research on this topic, described in [2] and [3], will also be discussed. The PQCC (Production-Quality Compiler-Compiler) project is an effort aimed at the automatic construction of production quality, optimizing compilers. The goal, is, with no more than a few man-months effort, to produce a compiler that is competitive in every respect with the best hand-crafted compilers available today. Input to this automatic construction process is formal descriptions of the source language and target machine. PQCC differs from nearly all previous work in this area in that we are concentrating on the semantic and machine-dependent phases of compilation—as opposed to lexical and syntactic analysis. Each phase has been formalized in a manner that permits it to be expressed in table-driven form. Thus the automatic construction of the compiler consists of deriving these tables from the semantic definitions of the language and target machine. Table-driven prototypes have just been completed for most compiler phases, and work is now proceeding on improving and automating their generation. The talk will go into some detail on one of these phases, code generation, discussing the formalization of the (table-driven) algorithms and the automatic construction of the tables from a machine description.