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AR# 3713

V1.4 COREGEN: Integer arithmetic overflow during VHDL behavioral simulation of SQRT (square root) function


Keywords: core generator, coregen, sqrt, square root, integer
arithmetic overflow, vhdl, 31

Urgency: standard

Pertinent release(s): v1.4.0

General Description:
Specifying an output width of 30 bits or higher for the
Square Root module may cause the behavioral model to generate
the following error:

Core parameters : Output_Width = 31, Input_Width = 60.
Simulation error :
**Error: vhdlsim,12:
Integer arithmetic overflow.
Warning: vhdlsim,313:
Can't display source line from file ul_utils.vhd. The file
could not be located using the USE environmental/setup file


This problem only affects the VHDL behavioral model for the

The reason why many of the modules delivered with COREGen
v1.4.x are limited to bus widths of 31 or less is
because of the way arithmetic operations are implemented in
the VHDL behavioral models. Most models convert incoming
operands from their binary (bit_vector) representations to
integers, perform any necessary arithmetic using the standard
set of VHDL arithmetic operators, and convert the results back
to bit_vectors for expression at the output ports.
Unfortunately, VHDL's integer datatype is restricted to
numbers in the range -2^31 to 2^31. As a result, the above
process can fail when busses with bit-widths over 31 bits
contain numbers outside this range.

This problem has been fixed with the v1.4.1 patch by
re-implementing the behavioral models
using bit-wise arithmetic instead of integer arithmetic, since
bit-wise arithmetic places no limit on bit width.

The patch is available at:

AR# 3713
日期 04/02/2002
状态 Archive
Type 综合文章