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add base support for signed multiplication over/under flow

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2024-01-30 12:47:28 -08:00
parent 2da3261d8a
commit 0dc204cd4a
5 changed files with 85 additions and 7 deletions
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26
src/sat/smt/intblast_solver.cpp
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@ -788,6 +788,32 @@ namespace intblast {
r = a.mk_lt(mul(umod(bv_expr, 0), umod(bv_expr, 1)), a.mk_int(bv_size(bv_expr)));
break;
}
case OP_BSMUL_NO_OVFL: {
bv_expr = e->get_arg(0);
expr* x = umod(bv_expr, 0), *y = umod(bv_expr, 1);
rational N = bv_size(bv_expr);
expr* lim = a.mk_int(N/2);
expr* signx = a.mk_ge(x, lim);
expr* signy = a.mk_ge(y, lim);
x = m.mk_ite(signx, a.mk_sub(a.mk_int(N), x), x);
y = m.mk_ite(signy, a.mk_sub(a.mk_int(N), y), y);
// signx != signy || x * y < N/2
r = m.mk_or(m.mk_not(m.mk_eq(signx, signy)), a.mk_lt(a.mk_mul(x, y), lim));
break;
}
case OP_BSMUL_NO_UDFL: {
bv_expr = e->get_arg(0);
expr* x = umod(bv_expr, 0), *y = umod(bv_expr, 1);
rational N = bv_size(bv_expr);
expr* lim = a.mk_int(N/2);
expr* signx = a.mk_ge(x, lim);
expr* signy = a.mk_ge(y, lim);
x = m.mk_ite(signx, a.mk_sub(a.mk_int(N), x), x);
y = m.mk_ite(signy, a.mk_sub(a.mk_int(N), y), y);
// signx == signy || x * y <= N/2
r = m.mk_or(m.mk_eq(signx, signy), a.mk_le(a.mk_mul(x, y), lim));
break;
}
case OP_BSHL: {
if (!a.is_numeral(arg(0)) && !a.is_numeral(arg(1)))
r = a.mk_shl(bv.get_bv_size(e), arg(0),arg(1));