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Fix for fp.rem. Fixes #2381.
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Christoph M. Wintersteiger committed Aug 15, 2019
1 parent 0edd587 commit 892aa12
Showing 1 changed file with 36 additions and 45 deletions.
81 changes: 36 additions & 45 deletions src/ast/fpa/fpa2bv_converter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1122,78 +1122,69 @@ void fpa2bv_converter::mk_rem(sort * s, expr_ref & x, expr_ref & y, expr_ref & r
a_lz_ext = m_bv_util.mk_zero_extend(2, a_lz);
b_lz_ext = m_bv_util.mk_zero_extend(2, b_lz);

expr_ref exp_diff(m), neg_exp_diff(m), exp_diff_is_neg(m), exp_diff_ge_zero(m);
expr_ref exp_diff(m), neg_exp_diff(m), exp_diff_is_neg(m), exp_diff_ge_zero(m), exp_diff_is_zero(m);
exp_diff = m_bv_util.mk_bv_sub(
m_bv_util.mk_bv_sub(a_exp_ext, a_lz_ext),
m_bv_util.mk_bv_sub(b_exp_ext, b_lz_ext));
neg_exp_diff = m_bv_util.mk_bv_neg(exp_diff);
exp_diff_is_neg = m_bv_util.mk_sle(exp_diff, m_bv_util.mk_numeral(0, ebits+2));
exp_diff_is_zero = m.mk_eq(exp_diff, m_bv_util.mk_numeral(0, ebits+2));
exp_diff_ge_zero = m_bv_util.mk_sle(m_bv_util.mk_numeral(0, m_bv_util.get_bv_size(exp_diff)), exp_diff);
dbg_decouple("fpa2bv_rem_exp_diff", exp_diff);

// CMW: This creates _huge_ bit-vectors, which is potentially sub-optimal,
// but calculating this via rem = x - y * nearest(x/y) creates huge
// circuits, too. Lazy instantiation seems the way to go in the long run
// (using the lazy bit-blaster helps on simple instances).
expr_ref a_sig_ext(m), b_sig_ext(m), lshift(m), rshift(m), shifted(m), huge_rem(m);
expr_ref a_sig_ext(m), b_sig_ext(m), lshift(m), rshift(m), shifted(m), huge_rem(m), huge_div(m), huge_div_is_even(m);
a_sig_ext = m_bv_util.mk_concat(m_bv_util.mk_zero_extend(max_exp_diff_ui, a_sig), m_bv_util.mk_numeral(0, 3));
b_sig_ext = m_bv_util.mk_concat(m_bv_util.mk_zero_extend(max_exp_diff_ui, b_sig), m_bv_util.mk_numeral(0, 3));
lshift = m_bv_util.mk_zero_extend(max_exp_diff_ui + sbits - (ebits+2) + 3, exp_diff);
rshift = m_bv_util.mk_zero_extend(max_exp_diff_ui + sbits - (ebits+2) + 3, neg_exp_diff);
shifted = m.mk_ite(exp_diff_is_neg, m_bv_util.mk_bv_ashr(a_sig_ext, rshift),
m_bv_util.mk_bv_shl(a_sig_ext, lshift));
huge_rem = m_bv_util.mk_bv_urem(shifted, b_sig_ext);
huge_div = m.mk_app(m_bv_util.get_fid(), OP_BUDIV_I, shifted, b_sig_ext);
huge_div_is_even = m.mk_eq(m_bv_util.mk_extract(0, 0, huge_div), m_bv_util.mk_numeral(0, 1));
dbg_decouple("fpa2bv_rem_exp_diff_is_neg", exp_diff_is_neg);
dbg_decouple("fpa2bv_rem_lshift", lshift);
dbg_decouple("fpa2bv_rem_rshift", rshift);
dbg_decouple("fpa2bv_rem_huge_rem", huge_rem);
dbg_decouple("fpa2bv_rem_huge_div", huge_div);

expr_ref rndd_sgn(m), rndd_exp(m), rndd_sig(m), rne_bv(m), rndd(m);
expr_ref rndd_sgn(m), rndd_exp(m), rndd_sig(m), rne_bv(m), rndd_sig_lz(m);
rndd_sgn = a_sgn;
rndd_exp = m_bv_util.mk_bv_sub(b_exp_ext, b_lz_ext);
rndd_sig = m_bv_util.mk_extract(sbits+3, 0, huge_rem);
rne_bv = m_bv_util.mk_numeral(BV_RM_TIES_TO_EVEN, 3);
round(s, rne_bv, rndd_sgn, rndd_sig, rndd_exp, rndd);

expr_ref y_half(m), ny_half(m), zero_e(m), two_e(m);
expr_ref y_half_is_zero(m), y_half_is_nz(m);
expr_ref r_ge_y_half(m), r_gt_ny_half(m), r_le_y_half(m), r_lt_ny_half(m);
expr_ref r_ge_zero(m), r_le_zero(m);
expr_ref rounded_sub_y(m), rounded_add_y(m);
mpf zero, two;
m_mpf_manager.set(two, ebits, sbits, 2);
m_mpf_manager.set(zero, ebits, sbits, 0);
mk_numeral(s, two, two_e);
mk_numeral(s, zero, zero_e);
mk_div(s, rne_bv, y, two_e, y_half);
mk_neg(s, y_half, ny_half);
mk_is_zero(y_half, y_half_is_zero);
y_half_is_nz = m.mk_not(y_half_is_zero);

mk_float_ge(s, rndd, y_half, r_ge_y_half);
mk_float_gt(s, rndd, ny_half, r_gt_ny_half);
mk_float_le(s, rndd, y_half, r_le_y_half);
mk_float_lt(s, rndd, ny_half, r_lt_ny_half);

mk_sub(s, rne_bv, rndd, y, rounded_sub_y);
mk_add(s, rne_bv, rndd, y, rounded_add_y);

expr_ref sub_cnd(m), add_cnd(m);
sub_cnd = m.mk_and(exp_diff_ge_zero,
m.mk_and(y_half_is_nz,
m.mk_or(m.mk_and(y_is_pos, r_ge_y_half),
m.mk_and(y_is_neg, r_le_y_half))));
add_cnd = m.mk_and(exp_diff_ge_zero,
m.mk_and(y_half_is_nz,
m.mk_or(m.mk_and(y_is_pos, r_lt_ny_half),
m.mk_and(y_is_neg, r_gt_ny_half))));

dbg_decouple("fpa2bv_rem_y_half", y_half);
mk_leading_zeros(rndd_sig, ebits+2, rndd_sig_lz);
dbg_decouple("fpa2bv_rem_rndd_sig", rndd_sig);
dbg_decouple("fpa2bv_rem_rndd_sig_lz", rndd_sig_lz);

SASSERT(m_bv_util.get_bv_size(rndd_exp) == ebits+2);
SASSERT(m_bv_util.get_bv_size(y_exp_m1) == ebits);

expr_ref rndd_exp_eq_y_exp_m1(m), y_sig_le_rndd_sig(m);
rndd_exp_eq_y_exp_m1 = m.mk_eq(rndd_sig_lz, m_bv_util.mk_numeral(2, ebits+2));
dbg_decouple("fpa2bv_rem_rndd_exp_eq_y_exp_m1", rndd_exp_eq_y_exp_m1);

expr_ref y_sig_ext(m), y_sig_eq_rndd_sig(m);
y_sig_ext = m_bv_util.mk_concat(m_bv_util.mk_zero_extend(2, b_sig), m_bv_util.mk_numeral(0, 2));
y_sig_le_rndd_sig = m_bv_util.mk_sle(y_sig_ext, rndd_sig);
y_sig_eq_rndd_sig = m.mk_eq(y_sig_ext, rndd_sig);
dbg_decouple("fpa2bv_rem_y_sig_ext", y_sig_ext);
dbg_decouple("fpa2bv_rem_y_sig_le_rndd_sig", y_sig_le_rndd_sig);
dbg_decouple("fpa2bv_rem_y_sig_eq_rndd_sig", y_sig_eq_rndd_sig);

expr_ref sub_cnd(m);
sub_cnd = m.mk_or(m.mk_and(rndd_exp_eq_y_exp_m1, y_sig_le_rndd_sig, m.mk_not(y_sig_eq_rndd_sig)),
m.mk_and(rndd_exp_eq_y_exp_m1, y_sig_eq_rndd_sig, m.mk_not(huge_div_is_even)));
dbg_decouple("fpa2bv_rem_sub_cnd", sub_cnd);
dbg_decouple("fpa2bv_rem_add_cnd", add_cnd);
dbg_decouple("fpa2bv_rem_rounded_add_y", rounded_add_y);
dbg_decouple("fpa2bv_rem_rounded_sub_y", rounded_sub_y);
dbg_decouple("fpa2bv_rem_rndd", rndd);

mk_ite(add_cnd, rounded_add_y, rndd, v7);
mk_ite(sub_cnd, rounded_sub_y, v7, v7);
expr_ref rndd(m), rounded_sub_y(m), rounded_add_y(m);
round(s, rne_bv, rndd_sgn, rndd_sig, rndd_exp, rndd);
mk_sub(s, rne_bv, rndd, y, rounded_sub_y);
mk_ite(sub_cnd, rounded_sub_y, rndd, v7);

// And finally, we tie them together.
mk_ite(c6, v6, v7, result);
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