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PROGRAM EXECUTION IN THE SYMBOL 2R COMPUTER

IP.com Disclosure Number: IPCOM000127988D
Original Publication Date: 1973-Dec-31
Included in the Prior Art Database: 2005-Sep-14
Document File: 6 page(s) / 26K

Publishing Venue

Software Patent Institute

Related People

Perry C. Hutchiison: AUTHOR [+4]

Abstract

The direct hardware implementation of the SYMBOL Programming Language (SPL) is highly dependent on an unusually powerful Central Processor(CP). This paper de-scribes the principal features of the CP1s operations in executing SPL programs.

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THIS DOCUMENT IS AN APPROXIMATE REPRESENTATION OF THE ORIGINAL.

PROGRAM EXECUTION IN THE SYMBOL 2R COMPUTER

Perry C. Hutchiison Karen Ethington

October 1973

This paper was presented at the Symposium on the High-Level Language Computer Architecture University of Maryland, College Park, Maryland November 1973

INTRODUCTION

The direct hardware implementation of the SYMBOL Programming Language (SPL) is highly dependent on an unusually powerful Central Processor(CP). This paper de-scribes the principal features of the CP1s operations in executing SPL programs.

CENTRAL PROCESSOR ORGANIZATION

The CP consists of four interdepen-dent sub-processors: 1. The Instruction Sequencer(IS) scans the object string and controls the overall execution process, calling on the other three sub-processors as needed. 2. The Arithmetic Processor(AP) performs arithmetic operations and numeric compari-sons at user-specified precision (up to 99 significant decimal digits). 3. The Format Processor (F P) performs string operations, lexicographic compari-sons, and conversion operations. 4. The Reference Processor(RP) initial-izes the values of variables, performs as- signment operations, manipulates and ac-cesses data structures(2), and decodes the flag fields of Name Table Control Words (1) to recognize label and parameter refer-ences, procedure- calls, GLOBAL indirec-tion, and the occurrence of ON-events(2).

DATA TYPES AND CONVERSIONS

ble to the user. Type information is carried with the data; type is a property associated with values rather than with identifiers. Thus, a particular identifi-er may have values of different types at different times. The operators available in the CP may be categorized by the types of operands upon which they are defined and which they produce as results (see Table I). SPL recognizes only one scalar data type -- the character string. Internally, however, it has been found convenient to utilize three types: Character Strings, Packed Floating-point Numerics, and Integers (see Figure I). Character Strings are the principal internal data type and are the type used in I/O opera-tions; Numerics are required for and re-sult from arithmetic operations. (The use of the packed format for arithmetic leads to simplification of the logic in the AP -see (7).) Integers are a transient type which can appear only on the stack (see below); they are used far subscripts, I/0 unit numbers, and values which are to be assigned to LIMIT. All necessary conver-sions between these three types are per-formed by the FP as needed and are invisi-

EVALUATION OF EXPRESSIONS

Iowa State University Page 1 Dec 31, 1973

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PROGRAM EXECUTION IN THE SYMBOL 2R COMPUTER

The CP uses a last-in-first-out push-down stack in evaluating expressions, which are stored in reverse Polish form and consist of operands and operators. (Since the stack is stored in a storage string(3), its length is practically un-limited.) As it scans the object string, the IS pushes operands...