| commit | 75b0e8006dd26dfc18df644a90cd1c8a305d65ce | [log] [tgz] |
|---|---|---|
| author | Rupert Swarbrick <rswarbrick@lowrisc.org> | Thu Aug 05 16:27:35 2021 +0100 |
| committer | Rupert Swarbrick <rswarbrick@gmail.com> | Thu Aug 05 19:20:45 2021 +0100 |
| tree | c3f766e522754bfde1930324f11e2fd2891cbee3 | |
| parent | d10437409f5d96cf48723525914412f2c55eb9fb [diff] |
[otbn,dv] Avoid integer overflow in coverpoint expression
The expression "1 << (32 - 1)" that you get when evaluating
DEF_SIGN_CP(name, value, 32) isn't representable as a signed 32-bit
integer and VCS emits warnings in the build log:
Warning-[CPBRM] Precision or Sign Mismatch
../src/lowrisc_dv_otbn_env_0.1/otbn_env_cov.sv, 977
Potential precision or sign mismatch in range values of user defined bin neg
of coverpoint sign_a_cp in covergroup
otbn_env_pkg::otbn_env_cov::insn_addsub_cg
Source info: bins neg = { [(1 << 31):32'hffffffff] } ;. Values outside the
valid coverpoint range will either be deleted(singleton values) or
adjusted(ranges) as per the precision semantics.
Intriguingly, it doesn't warn about the (1 << (32 - 1)) - 1.
Apparently, the conversion to signed 32-bit integer only happens at
the root of the expression tree.
Make the "1" an explicit width to avoid the problem.
Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
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