tree c3f766e522754bfde1930324f11e2fd2891cbee3
parent d10437409f5d96cf48723525914412f2c55eb9fb
author Rupert Swarbrick <rswarbrick@lowrisc.org> 1628177255 +0100
committer Rupert Swarbrick <rswarbrick@gmail.com> 1628187645 +0100

[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>