Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Particular function performed
Reexamination Certificate
1994-07-19
2001-05-01
Malzahn, David H. (Department: 2121)
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Particular function performed
Reexamination Certificate
active
06226664
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to signal processing technologies and more particularly to a method and device for adding and subtracting thermometer coded data.
BACKGROUND OF THE INVENTION
In certain applications, computation of maxima and minima is extensive. For such applications, it is desirable to represent a number in thermometer code since calculation of maxima or minima becomes a straightforward process. Thermometer coded data is used to indicate a specific value represented by the data. For example, the value of 5 in thermometer code is represented in binary form as 00011111 for an 8 bit data format. The more logic “1s” in the data in right justified order, the higher the value, and vice versa.
One disadvantage of a straight thermometer code is the number of bits required to represent a number e.g. 64 bits to represent a value of 63. One solution around this problem is to represent each digit of a multidigit number in thermometer code. To represent a value of 63, a two digit octal number can be used, one for each digit of the value. If each octal number has 8 bits, then 16 bits of data rather than 64 bits will be needed to represent the value.
Some computations will require arithmetic operations besides maxima and minima processing. Conventional signal processing technology cannot simply and accurately perform arithmetic operations on thermometer coded words. Further, conventional technology cannot perform arithmetic operation or multi digit representations of thermometer coded data. It is thus desirable to have a circuit which can perform addition and subtraction of thermometer coded words to enhance signal processing of data represented in thermometer code.
From the foregoing, it may be appreciated that a need has arisen for a method and device for processing thermometer coded data. A need has also arisen for a method and device which can perform arithmetic functions on thermometer coded data. A need has also arisen to perform arithmetic operations on multi digit representations of thermometer coded data. Further, a need has arisen for a method and device which can add and subtract two thermometer coded words.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and device for adding and subtracting thermometer coded data are provided which substantially eliminate or reduce disadvantages and problems associated with prior signal processing of thermometer coded data.
The present invention includes circuitry for determining whether a borrowing condition exists for a least significant byte of a thermometer coded word during an absolute value subtraction process. A borrowing condition exists if the most significant byte of word one is greater than the most significant byte of word two and the least significant byte of word two is greater than the least significant byte of word one, or vice versa. If no borrowing condition exists, the most significant bytes of the two words are subtracted from each other by an exclusive-or process and the result is reconstructed by shifting to the right the bit positions until the result is in proper thermometer code format. Similarly, the least significant bytes of the two words are subtracted from each other by an exclusive-or process to produce a result which is also shifted into proper thermometer code format. If a borrowing condition exists, the most significant byte of word one is shifted to the right once and the least significant byte of word two is translated in response to the borrowing condition before least significant byte subtraction occurs. The result of the subtraction is processed through a shift right, rotate left circuit to place the result, which becomes the resulting least significant byte of the absolute value subtraction function, into proper thermometer code format.
For an addition process, the first thermometer coded word is reversed and then subtracted by an exclusive-or process from the second thermometer coded word. The result of the addition is inverted and reconstructed into proper thermometer code format. If a carry condition exists on the least significant byte, as determined by a carry circuit, the most significant byte of the resulting word is adjusted by the carry to produce the final most significant byte. If a carry condition exists on the most significant byte, a carry flag is set indicating that the most significant byte includes a carry condition.
The present invention provides various technical advantages over thermometer code processing systems within the prior art. One technical advantage is in the ability to perform arithmetic functions on thermometer coded data. Another technical advantage is in providing addition and absolute value subtraction on thermometer coded data. Still another technical advantage is in the ability to perform separate arithmetic functions on the most significant bytes and the least significant bytes of desired thermometer coded words. Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.
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Decrements for reducing M-bids number, Anonymous Jan. 10, 1995.
Patent Abstracts of Japan, JP-A-60 014 326 Jan., 1985.
Mahant-Shetti Shivaling S.
Ng Fuk Ho P.
Brady III Wade James
Malzahn David H.
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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