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remove wtm and booth

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2021-08-27 15:27:11 -07:00
parent cd7a826083
commit e9a30385cf
2 changed files with 58 additions and 191 deletions
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8
src/ast/rewriter/bit_blaster/bit_blaster_tpl.h
View file

@ -35,16 +35,12 @@ protected:
void mk_ext_rotate_left_right(unsigned sz, expr * const * a_bits, expr * const * b_bits, expr_ref_vector & out_bits);
unsigned long long m_max_memory;
bool m_use_wtm; /* Wallace Tree Multiplier */
bool m_use_bcm; /* Booth Multiplier for constants */
void checkpoint();
public:
bit_blaster_tpl(Cfg const & cfg = Cfg(), unsigned long long max_memory = UINT64_MAX, bool use_wtm = false, bool use_bcm=false):
bit_blaster_tpl(Cfg const & cfg = Cfg(), unsigned long long max_memory = UINT64_MAX):
Cfg(cfg),
m_max_memory(max_memory),
m_use_wtm(use_wtm),
m_use_bcm(use_bcm) {
m_max_memory(max_memory) {
}
void set_max_memory(unsigned long long max_memory) {

129
src/ast/rewriter/bit_blaster/bit_blaster_tpl_def.h
View file

@ -204,7 +204,6 @@ void bit_blaster_tpl<Cfg>::mk_multiplier(unsigned sz, expr * const * a_bits, exp
return;
}
out_bits.reset();
if (!m_use_wtm) {
#if 0
static unsigned counter = 0;
counter++;
@ -271,82 +270,7 @@ void bit_blaster_tpl<Cfg>::mk_multiplier(unsigned sz, expr * const * a_bits, exp
out_bits.push_back(out);
}
}
}
else {
// WALLACE TREE MULTIPLIER
if (sz == 1) {
expr_ref t(m());
mk_and(a_bits[0], b_bits[0], t);
out_bits.push_back(t);
return;
}
// There are sz numbers to add and we use a Wallace tree to reduce that to two.
// In this tree, we reduce as early as possible, as opposed to the Dada tree where some
// additions may be delayed if they don't increase the propagation delay [which may be
// a little bit more efficient, but it's tricky to find out which additions create
// additional delays].
expr_ref zero(m());
zero = m().mk_false();
vector< expr_ref_vector > pps;
pps.resize(sz, expr_ref_vector(m()));
for (unsigned i = 0; i < sz; i++) {
checkpoint();
// The partial product is a_bits AND b_bits[i]
// [or alternatively ITE(b_bits[i], a_bits, bv0[sz])]
expr_ref_vector & pp = pps[i];
expr_ref t(m());
for (unsigned j = 0; j < i; j++)
pp.push_back(zero); // left shift by i bits
for (unsigned j = 0; j < (sz - i); j++) {
mk_and(a_bits[j], b_bits[i], t);
pp.push_back(t);
}
SASSERT(pps[i].size() == sz);
}
while (pps.size() != 2) {
unsigned save_inx = 0;
unsigned i = 0;
unsigned end = pps.size() - 3;
for ( ; i <= end; i += 3) {
checkpoint();
expr_ref_vector pp1(m()), pp2(m()), pp3(m());
pp1.swap(pps[i]);
pp2.swap(pps[i+1]);
pp3.swap(pps[i+2]);
expr_ref_vector & sum_bits = pps[save_inx];
expr_ref_vector & carry_bits = pps[save_inx+1];
SASSERT(sum_bits.empty() && carry_bits.empty());
carry_bits.push_back(zero);
mk_carry_save_adder(pp1.size(), pp1.data(), pp2.data(), pp3.data(), sum_bits, carry_bits);
carry_bits.pop_back();
save_inx += 2;
}
if (i == pps.size()-2) {
pps[save_inx++].swap(pps[i++]);
pps[save_inx++].swap(pps[i++]);
}
else if (i == pps.size()-1) {
pps[save_inx++].swap(pps[i++]);
}
SASSERT (save_inx < pps.size() && i == pps.size());
pps.shrink(save_inx);
}
SASSERT(pps.size() == 2);
// Now there are only two numbers to add, we can use a ripple carry adder here.
mk_adder(sz, pps[0].data(), pps[1].data(), out_bits);
}
}
@ -1258,15 +1182,11 @@ bool bit_blaster_tpl<Cfg>::mk_const_multiplier(unsigned sz, expr * const * a_bit
return true;
}
out_bits.reset();
if (!m_use_bcm) {
return false;
}
expr_ref_vector minus_b_bits(m()), tmp(m());
mk_neg(sz, b_bits, minus_b_bits);
out_bits.resize(sz, m().mk_false());
#if 1
bool last = false, now;
for (unsigned i = 0; i < sz; i++) {
now = m().is_true(a_bits[i]);
@ -1286,55 +1206,6 @@ bool bit_blaster_tpl<Cfg>::mk_const_multiplier(unsigned sz, expr * const * a_bit
last = now;
}
#else
// Radix 4 Booth encoder
// B = b_bits, -B = minus_b_bits
// 2B = b2_bits, -2B = minus_b2_bits
expr_ref_vector b2_bits(m());
expr_ref_vector minus_b2_bits(m());
b2_bits.push_back(m().mk_false());
minus_b2_bits.push_back(m().mk_false());
for (unsigned i = 0; i < sz-1; i++) {
b2_bits.push_back(b_bits[i]);
minus_b2_bits.push_back(minus_b_bits.get(i));
}
bool last=false, now1, now2;
for (unsigned i = 0; i < sz; i += 2) {
now1 = m().is_true(a_bits[i]);
now2 = m().is_true(a_bits[i+1]);
SASSERT(now1 || m().is_false(a_bits[i]));
SASSERT(now2 || m().is_false(a_bits[i+1]));
tmp.reset();
if ((!now2 && !now1 && last) ||
(!now2 && now1 && !last)) { // Add B
mk_adder(sz - i, out_bits.c_ptr() + i, b_bits, tmp);
for (unsigned j = 0; j < (sz - i); j++)
out_bits.set(i+j, tmp.get(j));
}
else if (!now2 && now1 && last) { // Add 2B
mk_adder(sz - i, out_bits.c_ptr() + i, b2_bits.c_ptr(), tmp);
for (unsigned j = 0; j < (sz - i); j++)
out_bits.set(i+j, tmp.get(j));
}
else if (now2 && !now1 && !last) { // Add -2B
mk_adder(sz - i, out_bits.c_ptr() + i, minus_b2_bits.c_ptr(), tmp);
for (unsigned j = 0; j < (sz - i); j++)
out_bits.set(i+j, tmp.get(j));
}
else if ((now2 && !now1 && last) ||
(now2 && now1 && !last)) { // Add -B
mk_adder(sz - i, out_bits.c_ptr() + i, minus_b_bits.c_ptr(), tmp);
for (unsigned j = 0; j < (sz - i); j++)
out_bits.set(i+j, tmp.get(j));
}
last = now2;
}
#endif
TRACE("bit_blaster_tpl_booth", for (unsigned i=0; i<out_bits.size(); i++)
tout << "Booth encoding: " << mk_pp(out_bits[i].get(), m()) << "\n"; );