Floating point addition pipeline including extreme value, comparison and accumulate functions

Abstract

A multimedia execution unit configured to perform vectored floating point and integer instructions. The execution unit may include an add / subtract pipeline having far and close data paths. The far path is configured to handle effective addition operations and effective subtraction operations for operands having an absolute exponent difference greater than one. The close path is configured to handle effective subtraction operations for operands having an absolute exponent difference less than or equal to one. The close path is configured to generate two output values, wherein one output value is the first input operand plus an inverted version of the second input operand, while the second output value is equal to the first output value plus one. Selection of the first or second output value in the close path effectuates the round-to-nearest operation for the output of the adder.

Description

[0001] 1. Field of the Invention[0002] This invention relates to floating point arithmetic within microprocessors, and more particularly to an add / subtract pipeline within a floating point arithmetic unit.[0003] 2. Description of the Related Art[0004] Numbers may be represented within computer systems in a variety of ways. In an integer format, for example, a 32-bit register may store numbers ranging from 0 to 2.sup.32 -1. (The same register may also signed numbers by giving up one order of magnitude in range). This format is limiting, however, since it is incapable of representing numbers which are not integers (the binary point in integer format may be thought of as being to the right of the least significant bit in the register).[0005] To accommodate non-integer numbers, a fixed point representation may be used. In this form of representation, the binary point is considered to be somewhere other than to the right of the least significant bit. For example, a 32-bit register may be...

AI Technical Summary

Problems solved by technology

This format is limiting, however, since it is incapable of representing numbers which are not integers (the binary point in integer format may be thought of as being to the right of the least significant bit in the register).

Although floating point addition is related to fixed point addition, two differences cause complications.

Secondly, rounding must be performed.

The result produced by the close data path is thus speculative.

Floating point software is typically written to manipulate numbers that are either very large or small, require a great deal of precision, or result from complex mathematical operations such as transcendentals.

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