US 2003/0115236 A1 · Elimination of rounding step in the short path of a floating point adder

Abstract

The apparatus and method of the present invention operates to perform a floating-point operation involving at least two operands in floating-point representation. The apparatus comprises two concurrent data paths, a short path and a long path. The short path is used to produce a result of the floating-point operation if the floating-point operation is a subtract operation and the exponent difference of the two operands is 0, or if the floating-point operation is a subtract operation, the exponent difference is 1, and the mantissa of the operand with a larger exponent is within a predetermined number range. The long path is used to produce a result of the floating-point operation if the floating point operation is an addition operation, or if it is a subtraction operation and the exponent difference is larger than one, or if it is a subtract operation, the exponent difference is 1, and the mantissa of the operand with the larger exponent is within another predetermined number range. Using this logic for selecting a data path for the floating-point operation, the short path does not require means such as an incrementer for post subtraction normalization.

Claims10

Dependent claims

In a floating-point adder having a long path and a short path, a method of selecting the path for a subtraction operation involving two operands, each operand having a mantissa and an exponent, the method comprising:

responsive to a difference between the exponents of the two operands being greater than one, selecting the long path;
responsive to a difference between the exponents of the two operands being zero, selecting the short path;
responsive to the difference between the exponents of the two operands being one, and the mantissa of the operand with a larger exponent being in a first predetermined number range, selecting the short path;
and
responsive to the difference between the exponent of the larger operand and the exponent of the smaller operand being one, and the mantissa of the larger operand being in a second predetermined number range, selecting the long path.

2 more elements

In a floating-point adder unit having two concurrent data paths, a short path and a long path, each data path producing a result for a floating-point operation involving two operands, each operand having a mantissa and an exponent, a method for selecting a result between the result produced by the short path and the result produced by the long path, comprising:

in response to the floating point operation being an addition operation, selecting the result produced by the long path;
in response to the floating point operation being a subtract operation and a difference between the exponents of the two operands being larger than 1, selecting the result produced by the long path;
in response to the floating point operation being a subtract operation and a difference between the exponents of the two operands being 0, selecting the result produced by the short path
in response to the floating point operation being a subtract operation, the difference between the exponents of the two operands being 1, and the mantissa of the operand with a larger exponent being in a first predetermined number range, selecting the result produced by the short path;
and
in response to the floating point operation being a subtract operation, the difference between the exponents, of the two operands being 1, and the mantissa of the operand with a larger exponent being in second predetermined number range, selecting the result produced by the long path.

3 more elements

Dependencies are inferred from the claim text.

Elimination of rounding step in the short path of a floating point adder

Life of this patent

Elimination of rounding step in the short path of a floating point adder

Life of this patent

Abstract

Claims10