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Fixing undefined behaviours #4879

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merged 2 commits into from
Feb 3, 2025
Merged

Fixing undefined behaviours #4879

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31b00b4
celledges: Use b_width_capped for left shifts
KrystalDelusion Jan 30, 2025
cf52cf3
nowrshmsk: Check for stride==0
KrystalDelusion Jan 30, 2025
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celledges: Use b_width_capped for left shifts 
`b_width_capped` already exists for preventing arithmetic overflow, limiting the value of `b_width` to 30.  This just changes the left shifts to also use it.
The caveat of incorrect results for extremely large values of `a_width` still applies, as does the improbability of that actually happening.
This fixes #4844 (or at least, the floating point exception; the circuit still isn't valid but I think that's fine).
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@KrystalDelusion
KrystalDelusion authored Jan 30, 2025
commit 31b00b4c72f89cf7e9e61733141838cf7819f2db
6 changes: 3 additions & 3 deletions kernel/celledges.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -253,13 +253,13 @@ void shift_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
if (a_width == 1 && is_signed) {
int skip = 1 << (k + 1);
int base = skip -1;
if (i % skip != base && i - a_width + 2 < 1 << b_width)
if (i % skip != base && i - a_width + 2 < 1 << b_width_capped)
db->add_edge(cell, ID::B, k, ID::Y, i, -1);
} else if (is_signed) {
if (i - a_width + 2 < 1 << b_width)
if (i - a_width + 2 < 1 << b_width_capped)
db->add_edge(cell, ID::B, k, ID::Y, i, -1);
} else {
if (i - a_width + 1 < 1 << b_width)
if (i - a_width + 1 < 1 << b_width_capped)
db->add_edge(cell, ID::B, k, ID::Y, i, -1);
}
// right shifts
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