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AR# 8983

3.1i COREGEN: 4K 8x8 Speed Optimized 8x8 multiplier does not work correctly for A = -128

Description

Keywords: 4000, multiplier, core generator, 2.1i, 3.1i

Urgency: hot

General Description:
The CORE Generator 4K 8x8 Speed Optimized 8x8 multiplier does not work
correctly for A = -128 when B is a negative number. In simulation, it is
observed that the MSB of the product gets replaced with a zero.

This problem only shows itself when the A input is equal to -128, the largest
magnitude negative number that can be represented with 8 bits. Feeding
this same value into the B input does not cause this problem.

Solution

If possible, use the B input for data values that may go as negative as -128.

Alternatively, you can use the Area-Optimized Multiplier, specifying input
widths of 8 bits for the A and B inputs, but the drawback is that you might
observe a slight reductiion in performance.
AR# 8983
Date Created 04/05/2000
Last Updated 08/23/2002
Status Archive
Type General Article