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Fix off-by-one in fp.div bit-blasting. Inspired by #4841 but doesn't quite fix it.

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Christoph M. Wintersteiger 2021-09-15 16:29:06 +00:00
parent c24f438e51
commit 738783a26c
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GPG key ID: BCF6360F86294467
1 changed files with 10 additions and 1 deletions
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11
src/ast/fpa/fpa2bv_converter.cpp
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@ -982,6 +982,8 @@ void fpa2bv_converter::mk_div(sort * s, expr_ref & rm, expr_ref & x, expr_ref &
// b_sig_ext can't be 0 here, so it's safe to use OP_BUDIV_I
quotient = m.mk_app(m_bv_util.get_fid(), OP_BUDIV_I, a_sig_ext, b_sig_ext);
dbg_decouple("fpa2bv_div_a_sig_ext", a_sig_ext);
dbg_decouple("fpa2bv_div_b_sig_ext", b_sig_ext);
dbg_decouple("fpa2bv_div_quotient", quotient);
SASSERT(m_bv_util.get_bv_size(quotient) == (sbits + sbits + extra_bits));
@ -989,6 +991,7 @@ void fpa2bv_converter::mk_div(sort * s, expr_ref & rm, expr_ref & x, expr_ref &
expr_ref sticky(m);
sticky = m.mk_app(m_bv_util.get_fid(), OP_BREDOR, m_bv_util.mk_extract(extra_bits-2, 0, quotient));
res_sig = m_bv_util.mk_concat(m_bv_util.mk_extract(extra_bits+sbits+1, extra_bits-1, quotient), sticky);
dbg_decouple("fpa2bv_div_sticky", sticky);
SASSERT(m_bv_util.get_bv_size(res_sig) == (sbits + 4));
@ -996,15 +999,21 @@ void fpa2bv_converter::mk_div(sort * s, expr_ref & rm, expr_ref & x, expr_ref &
mk_leading_zeros(res_sig, sbits + 4, res_sig_lz);
dbg_decouple("fpa2bv_div_res_sig_lz", res_sig_lz);
expr_ref res_sig_shift_amount(m);
res_sig_shift_amount = m_bv_util.mk_bv_sub(res_sig_lz, m_bv_util.mk_numeral(1, sbits + 4));
res_sig_shift_amount = m_bv_util.mk_bv_sub(res_sig_lz, m_bv_util.mk_numeral(2, sbits + 4));
dbg_decouple("fpa2bv_div_res_sig_shift_amount", res_sig_shift_amount);
expr_ref shift_cond(m);
shift_cond = m_bv_util.mk_ule(res_sig_lz, m_bv_util.mk_numeral(1, sbits + 4));
expr_ref res_sig_shifted(m), res_exp_shifted(m);
res_sig_shifted = m_bv_util.mk_bv_shl(res_sig, res_sig_shift_amount);
res_exp_shifted = m_bv_util.mk_bv_sub(res_exp, m_bv_util.mk_extract(ebits + 1, 0, res_sig_shift_amount));
dbg_decouple("fpa2bv_div_res_sig", res_sig);
dbg_decouple("fpa2bv_div_res_exp", res_exp);
dbg_decouple("fpa2bv_div_res_sig_shifted", res_sig_shifted);
dbg_decouple("fpa2bv_div_res_exp_shifted", res_exp_shifted);
m_simp.mk_ite(shift_cond, res_sig, res_sig_shifted, res_sig);
m_simp.mk_ite(shift_cond, res_exp, res_exp_shifted, res_exp);
dbg_decouple("fpa2bv_div_shift_cond", shift_cond);
round(s, rm, res_sgn, res_sig, res_exp, v8);