Browse Prior Art Database

Method For Generating Floating Point Status Word Control Bits

IP.com Disclosure Number: IPCOM000006388D
Publication Date: 2001-Dec-28
Document File: 2 page(s) / 1K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a compact method for generating floating-point status word control bits.

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Method For Generating Floating Point Status Word Control Bits

Disclosed is a compact method for generating floating-point status word control bits.

Some microprocessor designs include a floating-point engine that requires that the floating-point control fields be passed down the pipe along with every floating-point operation.  These control fields typically contain the following information:

·        invalid operand exception mask

·        denormal operand exception mask

·        zero-divide exception mask

·        overflow exception mask

·        underflow exception mask

·        inexact exception mask

·        rounding control

·        precision control

·        widest range exponent

·        src1 unnormals ok

·        src2 unnormals ok

·        src3 unnormals ok

·        ftz

·        nulti_nan_swa

·        update FPSW

·        MMX2 bit

Each portion of this control can be generated from either the floating-point control word or from a constant that is determined for the particular operation.  Typically, this was implemented using a 15-1 20-bit multiplexor.  The disclosed method replaces this large multiplexor with a much smaller ROM/2-1 multiplexing structure.

The disclosed method implements the control bit generation using read only memory (ROM).  The ROM contains two pieces of information for each field in the control word.  One piece of information states whether or not this information is coming from the architectural floating point control word.  The other piece of information tells what the constant for that field would be if it does not come from the floating-point control word. Fi...