Logarithm/inverse-logarithm converter and method of using same

• US 5,642,305 A
• Filed: 01/31/1995
• Issued: 06/24/1997
• Est. Priority Date: 01/31/1995
• Status: Expired due to Term

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wang, Shay-Ping Thomas, Pan, ShaoWei
• Primary Examiner(s): Gordon, Paul P.
• Assistant Examiner(s): MOISE, EMMANUEL LIONEL
• Application Number:
  US08/381,368
• Time in Patent Office: 875 Days
• Field of Search: 364/722, 364/748, 364/748.5, 364/715.03, 364/736, 364/857, 341/75
• US Class Current: 708/517
• CPC Class Codes: G06F 1/0356 by using two or more smaller tables, e.g. addressed by parts of the argument
• CPC Class Codes: G06F 2101/10 Logarithmic or exponential functions
• CPC Class Codes: H03M 7/50 Conversion to or from non-linear codes, e.g. companding

Abstract

A converter, which may be used for implementing either logarithmic or inverse-logarithmic functions, includes a memory, a multiplier, and an adder. The memory stores a plurality of parameters which are derived using a least squares method to estimate a logarithmic or inverse-logarithmic function over a domain of input values.

Claims

1. A logarithm converter, which comprises:

a memory for storing a plurality of parameters, wherein the parameters are calculated using a least squares method to estimate a logarithmic function over a domain of input values; and

arithmetic means, operatively coupled to the memory, for generating a log value by performing arithmetic operations on an input value and ones of the plurality of parameters which correspond to the input value.

2. The logarithm converter of claim 1, wherein the logarithmic function is estimated with a first order equation having two parameters.

3. The logarithm converter of claim 2, wherein the ones of the plurality of parameters include a first-order parameter and a zero-order parameter, and the arithmetic means includes:

a multiplier for multiplying the input value with the first-order parameter to produce a proportional term; and

an adder for summing the proportional term and the zero-order parameter to generate the log value.

4. The logarithm converter of claim 2, wherein the ones of the plurality of parameters include a first-order parameter and a zero-order parameter, and the arithmetic means includes:

a multiplier for multiplying a bit slice of the input value with the first-order parameter to produce a proportional term; and

an adder for summing the proportional term and the zero-order parameter to generate the log value.

5. The logarithm converter of claim 1, wherein the input value is a binary value having a plurality of bits used to retrieve from the memory the ones of the plurality of parameters.

6. A logarithm converter for generating a log value corresponding to an input value, the logarithm converter comprising:

a memory for storing a plurality of parameter pairs, wherein each of the plurality of parameter pairs is calculated using a least squares method to estimate a logarithmic function over an interval of input values, the memory providing as output a parameter pair corresponding to the input value, wherein the parameter pair has a first-order parameter and a zero-order parameter;

a multiplier for producing a proportional term by multiplying the input value with the first-order parameter; and

an adder for producing the log value by summing the proportional term and the zero-order parameter.

7. The logarithm converter of claim 6, wherein the input value is a binary value having a plurality of bits used to retrieve the parameter pair from the memory.

8. The logarithm converter of claim 6, wherein the logarithmic function is estimated with a first order equation.

9. A computing device, which comprises:

a processing unit for executing a computer operation which utilizes a log value;

a computer memory for storing a computer program which includes the computer operation;

a bus for connecting the processing unit and the computer memory; and

a logarithm converter which receives an input value and includes;

a memory for storing a plurality of parameters, wherein the plurality of parameters are calculated using a least squares method to estimate a logarithmic function over a domain of input values; and

arithmetic means, operatively coupled to the memory, for generating the log value by performing arithmetic operations on the input value and ones of the plurality of parameters which correspond to the input value.

10. The computing device of claim 9, wherein the logarithmic function is estimated with a first order equation having two parameters.

11. The computing device of claim 9, wherein the plurality of parameters include a first-order parameter and a zero-order parameter, and the arithmetic means includes:

a multiplier for multiplying the input value with the first-order parameter to produce a proportional term; and

an adder for summing the proportional term and the zero-order parameter to generate the log value.

12. The computing device of claim 9, wherein the input value is a binary value having a plurality of bits used to retrieve from the memory the ones of the plurality of parameters.

13. An inverse-logarithm converter, which comprises:

a memory for storing a plurality of parameters, wherein the plurality of parameters are calculated using a least squares method to estimate an inverse-logarithmic function over a domain of input values; and

arithmetic means, operatively coupled to the memory, for generating an inverse-log value by performing arithmetic operations on an input value and ones of the plurality of parameters which correspond to the input value.

14. The inverse-logarithm converter of claim 13, wherein the inverse-logarithmic function is estimated with a first order equation having two parameters.

15. The inverse-logarithm converter of claim 14, wherein the ones of the plurality of parameters include a first-order parameter and a zero-order parameter, and the arithmetic means includes:

a multiplier for multiplying the input value with the first-order parameter to produce a proportional term; and

an adder for summing the proportional term and the zero-order parameter to generate the inverse-log value.

16. The inverse-logarithm converter of claim 14, wherein the ones of the plurality of parameters include a first-order parameter and a zero-order parameter, and the arithmetic means includes:

a multiplier for multiplying a bit slice of the input value with the first-order parameter to produce a proportional term; and

an adder for summing the proportional term and the zero-order parameter to generate the inverse-log value.

17. The inverse-logarithm converter of claim 13, wherein the input value is a binary value having a plurality of bits used to retrieve from the memory the ones of the plurality of parameters.

18. An inverse-logarithm converter for generating an inverse-log value corresponding to an input value, the inverse-logarithm converter comprising:

a memory for storing a plurality of parameter pairs, wherein each of the plurality of parameter pairs is calculated using a least squares method to estimate an inverse-logarithmic function over an interval of input values, the memory providing as output a parameter pair corresponding to the input value, wherein the parameter pair has a first-order parameter and a zero-order parameter;

a multiplier for producing a proportional term by multiplying the input value with the first-order parameter; and

an adder for producing the inverse-log value by summing the proportional term and the zero-order parameter.

19. The inverse-logarithm converter of claim 18, wherein the input value is a binary value having a plurality of bits used to retrieve the parameter pair from the memory.

20. The inverse-logarithm converter of claim 18, wherein the inverse-logarithmic function is estimated with a first order equation.

21. A computing device, which comprises:

a processing unit for executing a computer operation which utilizes an inverse-log value;

a computer memory for storing a computer program which includes the computer operation;

a bus for connecting the processing unit and the computer memory; and

an inverse-logarithm converter which receives an input value and includes;

a memory for storing a plurality of parameters, wherein the plurality of parameters are calculated using a least squares method to estimate an inverse-logarithmic function over a domain of input values; and

arithmetic means, operatively coupled to the memory, for generating the inverse-log value by performing arithmetic operations on the input value and ones of the plurality of parameters which correspond to the input value.

22. The computing device of claim 21, wherein the inverse-logarithmic function is estimated with a first order equation having two parameters.

23. The computing device of claim 21, wherein the plurality of parameters include a first-order parameter and a zero-order parameter, and the arithmetic means includes:

a multiplier for multiplying the input value with the first-order parameter to produce a proportional term; and

an adder for summing the proportional term and the zero-order parameter to generate the inverse-log value.

24. The computing device of claim 21, wherein the input value is a binary value having a plurality of bits used to retrieve from the memory the ones of the plurality of parameters.