Fixed_Length_Bit_String

Index:

Abstract
Calendar
Project Development
Findings and Contributions
Links and References
Return to Europa

Abstract:

One of the components in RESOLVE is the Integer. Unlike the int in C, the Integer does not have any bitwise operations. In fact, access to simple bits is not available through RESOLVE. This component allows users to create and manipulate a string of bits (including conversion to/from Integer).

Calendar:

30 April 2002: A presentation to Europa proposed adding bitwise operations to the Integer component. Due to the strong opposition of several members, this project was begun as a replacement for integer bitwise operations.
• Spring Quarter 2002:
  • Development on all of the abstract components of Fixed_Length_Bit_String. Abstract components for individual-bit get/set; conversion to/from Integer; string-wide and, or, not, and exclusive or operations; and bit shifting left/right are completed.
  • Concrete kernel and enhanced operations mostly completed. Kernel component implements only the get/set operations. Enhanced component implements all operations.
  • Documentation completed. Fixed_Length_Bit_String component documentation was designed in the style used in "Software Component Engineering" Appendix B.
  • Addition of the Length operation, allowing users to know the length of a Fixed_Length_Bit_String after instantiation. Operation will be available in both the Kernel and Enhanced implementations. Operation has already been documented.
• Winter Quarter 2003
  • With most of the work apparently done, a presentation on the current status and contents of Fixed_Length_Bit_String was given.
  • Due to various points that were raised during the presentation, changes have been made to several abstract components. The changes have been propagated to the documentation.
  • The updated documentation is being finalized, with various layout issues being resolved.
• Spring Quarter 2003:
  • A. Karl Kornel is using this component as part of his work in CIS 560. Any bugs found during this use will be immediately integrated into the current version.
  • Two extensions have been developed to allow two-way conversion between an Integer and a substring of an already-existing Fixed_Length_Bit_String object.
• As of Winter Quarter 2005, this project is marked as completed. Revisions, corrections, and new components may be added at any time.

Project Development:

• One of the questions that came up in the project was how to internally store a string of bits. One option was to use an Array/Static_Array/Sequence of Integers. That would allow the use of an accessor instead of get/set operations. However, several problems came up. Using an entire integer to store a single bit would be a large waste of space. In addition, since the accessor returns a reference to an Integer, it would be possible to use the accessor to set values other than one and zero. Because of these problems, separate get and set operations are used to replace the accessor.
• Original plans specified an implementation of Fixed_Length_Bit_String that would have a required String_Length of 32 bits. That would allow the implementation to use a C int to store the bits, and would allow bitwise operations to be used, making the operations as fast as possible.
• Currently, the implementations of Fixed_Length_Bit_String use an Array/Static_Array of C unsigned ints. The array bounds are based on the requested string length. This eliminated the need for a special implementation, allowing for minimum operating time while allowing for any string length.
• Documentation for the component is in the same format as the component documentation in Appendix B of "Software Component Engineering". This required learning some of the finer points of Microsoft Office X to duplicate the style of the documentation, determined by analyzing some source files used to produce Appendix B. The CCD graphics were produced using sample files made in Canvas. Sample file for Office and Canvas were provided by Bruce Weide.

Findings and Contributions:

Current findings are now available in several forms. Additional information can be found in the Links and References section below.
• Code for the Fixed_Length_Bit_String component
  • Abstract component descriptions
  • Concrete components, both the Kernel and Enhanced components.
• PDF Documentation, in the format used by Software Component Engineering, Appendix B.
  • If you view PDF files in your web browser, click here to view the PDF in a new window.

Links and References:

• The current version of the documentation is available on the Sun systems at ~kornel/europa/fixed_length_bit_string. Documentation is provided in PDF and PostScript format.
• Test programs are also available on the Sun systems at ~kornel/europa/resolve_plus/Test/Fixed_Length_Bit_String. The test programs allow for testing of both implementations of Fixed_Length_Bit_String. A test program is also available to test the available extensions.
• The presentation that I gave on 23 January 2003 is available for viewing online, or in PDF form showing notes and slides or slides only.

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