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Bugfix for fp.fma. Fixes #872.

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This commit is contained in:
Christoph M. Wintersteiger 2017-07-28 20:16:13 +01:00
parent 33ebdc8adc
commit 0610392a05
3 changed files with 79 additions and 57 deletions
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85
src/util/mpf.cpp
View file

@ -556,8 +556,6 @@ void mpf_manager::add_sub(mpf_rounding_mode rm, mpf const & x, mpf const & y, mp
SASSERT(exp_delta <= INT_MAX);
scoped_mpz sticky_rem(m_mpz_manager);
m_mpz_manager.machine_div_rem(b.significand(), m_powers2((int)exp_delta), b.significand(), sticky_rem);
if (!m_mpz_manager.is_zero(sticky_rem) && m_mpz_manager.is_even(b.significand()))
m_mpz_manager.inc(b.significand());
TRACE("mpf_dbg", tout << "A' = " << m_mpz_manager.to_string(a.significand()) << std::endl;);
TRACE("mpf_dbg", tout << "B' = " << m_mpz_manager.to_string(b.significand()) << std::endl;);
@ -566,10 +564,14 @@ void mpf_manager::add_sub(mpf_rounding_mode rm, mpf const & x, mpf const & y, mp
if (sgn(a) != sgn(b)) {
TRACE("mpf_dbg", tout << "SUBTRACTING" << std::endl;);
m_mpz_manager.sub(a.significand(), b.significand(), o.significand);
if (!sticky_rem.is_zero() && m_mpz_manager.is_even(o.significand))
m_mpz_manager.dec(o.significand);
}
else {
TRACE("mpf_dbg", tout << "ADDING" << std::endl;);
m_mpz_manager.add(a.significand(), b.significand(), o.significand);
if (!sticky_rem.is_zero() && m_mpz_manager.is_even(o.significand))
m_mpz_manager.inc(o.significand);
}
TRACE("mpf_dbg", tout << "sum[-2:sbits+2] = " << m_mpz_manager.to_string(o.significand) << std::endl;);
@ -805,7 +807,7 @@ void mpf_manager::fma(mpf_rounding_mode rm, mpf const & x, mpf const & y, mpf co
o.ebits = x.ebits;
o.sbits = x.sbits;
scoped_mpf mul_res(*this, x.ebits+2, 2*x.sbits-1);
scoped_mpf mr(*this);
scoped_mpf a(*this, x.ebits, x.sbits), b(*this, x.ebits, x.sbits), c(*this, x.ebits, x.sbits);
set(a, x);
set(b, y);
@ -828,20 +830,18 @@ void mpf_manager::fma(mpf_rounding_mode rm, mpf const & x, mpf const & y, mpf co
SASSERT(m_mpz_manager.ge(b.significand(), m_powers2(x.sbits-1)));
// A/B in _1.[sbits-1].
mul_res.get().sign = (a.sign() != b.sign());
mul_res.get().exponent = a.exponent() + b.exponent();
m_mpz_manager.mul(a.significand(), b.significand(), mul_res.significand());
mr.set(x.ebits+2, 2*x.sbits-1, a.sign() != b.sign(), a.exponent() + b.exponent());
m_mpz_manager.mul(a.significand(), b.significand(), mr.significand());
TRACE("mpf_dbg", tout << "M = " << to_string(mul_res) << std::endl;
tout << "M = " << to_string_binary(mul_res, 1, 0) << std::endl;);
TRACE("mpf_dbg", tout << "M = " << to_string(mr) << std::endl;
tout << "M = " << to_string_binary(mr, 1, 0) << std::endl;);
// mul_res is [-1][0].[2*sbits - 2], i.e., >= 2^(2*sbits-2) and < 2^(2*sbits).
SASSERT(m_mpz_manager.lt(mul_res.significand(), m_powers2(2*x.sbits)));
SASSERT(m_mpz_manager.ge(mul_res.significand(), m_powers2(2*x.sbits - 2)));
SASSERT(m_mpz_manager.lt(mr.significand(), m_powers2(2*x.sbits)));
SASSERT(m_mpz_manager.ge(mr.significand(), m_powers2(2*x.sbits - 2)));
// Introduce extra bits into c in _[0].[sbits-1] s.t. c in _[0].[2*sbits-2]
c.get().ebits = x.ebits + 2;
c.get().sbits = 2 * x.sbits - 1;
c.set(x.ebits + 2, 2 * x.sbits - 1, c.sign(), c.exponent(), c.significand());
m_mpz_manager.mul2k(c.significand(), x.sbits - 1);
TRACE("mpf_dbg", tout << "C_= " << to_string(c) << std::endl;
@ -851,67 +851,67 @@ void mpf_manager::fma(mpf_rounding_mode rm, mpf const & x, mpf const & y, mpf co
SASSERT(m_mpz_manager.is_zero(c.significand()) ||
m_mpz_manager.ge(c.significand(), m_powers2(2*x.sbits - 2)));
if (exp(c) > exp(mul_res)) {
if (exp(c) > exp(mr)) {
TRACE("mpf_dbg", tout << "Swap!" << std::endl;);
mul_res.swap(c);
mr.swap(c);
}
mpf_exp_t exp_delta_w = exp(mul_res) - exp(c);
SASSERT(exp(mul_res) >= exp(c) && exp_delta_w >= 0);
// Alignment shift with sticky bit computation.
mpf_exp_t exp_delta_w = exp(mr) - exp(c);
SASSERT(exp(mr) >= exp(c) && exp_delta_w >= 0);
if (exp_delta_w > 2 * x.sbits)
exp_delta_w = 2 * x.sbits;
unsigned exp_delta = (unsigned)exp_delta_w;
TRACE("mpf_dbg", tout << "exp_delta = " << exp_delta << std::endl;);
// Alignment shift with sticky bit computation.
unsigned exp_delta = (unsigned)exp_delta_w;
scoped_mpz sticky_rem(m_mpz_manager);
m_mpz_manager.machine_div_rem(c.significand(), m_powers2(exp_delta), c.significand(), sticky_rem);
TRACE("mpf_dbg", tout << "alignment shift -> sig = " << m_mpz_manager.to_string(c.significand()) <<
TRACE("mpf_dbg", tout << "alignment shift by delta=" << exp_delta << " -> sig = " << m_mpz_manager.to_string(c.significand()) <<
" sticky_rem = " << m_mpz_manager.to_string(sticky_rem) << std::endl;);
if (!m_mpz_manager.is_zero(sticky_rem) && m_mpz_manager.is_even(c.significand()))
m_mpz_manager.inc(c.significand());
bool alignment_sticky = !m_mpz_manager.is_zero(sticky_rem);
TRACE("mpf_dbg", tout << "M'= " << m_mpz_manager.to_string(mul_res.significand()) << std::endl;
tout << "M'= " << to_string_binary(mul_res, 1, 0) << std::endl; );
TRACE("mpf_dbg", tout << "M'= " << m_mpz_manager.to_string(mr.significand()) << std::endl;
tout << "M'= " << to_string_binary(mr, 1, 0) << std::endl; );
TRACE("mpf_dbg", tout << "C'= " << m_mpz_manager.to_string(c.significand()) << std::endl;
tout << "C'= " << to_string_binary(c, 1, 0) << std::endl; );
scoped_mpf res(c);
res.get().sign = mul_res.sign();
res.get().exponent = mul_res.exponent();
// Significand addition
scoped_mpf res(mr);
if (sgn(mul_res) != sgn(c)) {
if (sgn(mr) != sgn(c)) {
TRACE("mpf_dbg", tout << "SUBTRACTING" << std::endl;);
m_mpz_manager.sub(mul_res.significand(), c.significand(), res.significand());
m_mpz_manager.sub(mr.significand(), c.significand(), res.significand());
if (alignment_sticky && m_mpz_manager.is_even(res.significand()))
m_mpz_manager.dec(res.get().significand);
if (m_mpz_manager.is_neg(res.significand())) {
m_mpz_manager.abs(res.significand());
res.get().sign |= !mul_res.sign() && c.sign();
res.get().sign |= c.sign();
}
}
else {
TRACE("mpf_dbg", tout << "ADDING" << std::endl;);
m_mpz_manager.add(mul_res.significand(), c.significand(), res.significand());
m_mpz_manager.add(mr.significand(), c.significand(), res.significand());
if (alignment_sticky && m_mpz_manager.is_even(res.significand()))
m_mpz_manager.inc(res.get().significand);
}
TRACE("mpf_dbg", tout << "S'= " << m_mpz_manager.to_string(res.significand()) << std::endl;
tout << "S'= " << to_string_binary(res, 1, 0) << std::endl; );
bool renorm_sticky = false;
SASSERT(m_mpz_manager.lt(res.significand(), m_powers2(2 * x.sbits + 1)));
if (m_mpz_manager.ge(res.significand(), m_powers2(2 * x.sbits)))
{
SASSERT(exp(res) < mk_max_exp(x.ebits)); // NYI.
res.get().exponent++;
bool sticky = !m_mpz_manager.is_even(res.significand());
renorm_sticky = !m_mpz_manager.is_even(res.significand());
m_mpz_manager.machine_div2k(res.significand(), 1);
if (sticky && m_mpz_manager.is_even(res.significand()))
m_mpz_manager.inc(res.significand());
TRACE("mpf_dbg", tout << "Add/Sub overflew into 4.xxx!" << std::endl;
tout << "S*= " << to_string_binary(res, 2, 0) << std::endl;);
}
@ -919,17 +919,18 @@ void mpf_manager::fma(mpf_rounding_mode rm, mpf const & x, mpf const & y, mpf co
set(o, x.ebits, x.sbits, res.sign(), res.exponent(), mpz(0));
if (x.sbits >= 4) {
m_mpz_manager.set(sticky_rem, 0);
m_mpz_manager.machine_div_rem(res.significand(), m_powers2(x.sbits - 4), o.significand, sticky_rem);
if (!m_mpz_manager.is_zero(sticky_rem) && m_mpz_manager.is_even(o.significand))
m_mpz_manager.inc(o.significand);
renorm_sticky |= !m_mpz_manager.is_zero(sticky_rem);
}
else {
m_mpz_manager.mul2k(res.significand(), 4 - x.sbits, o.significand);
}
if (renorm_sticky && m_mpz_manager.is_even(o.significand))
m_mpz_manager.inc(o.significand);
TRACE("mpf_dbg", tout << "sum[-1:sbits+2] = " << m_mpz_manager.to_string(o.significand) << std::endl;
tout << "R = " << to_string_binary(o, 2, 3) << std::endl;);
tout << "R = " << to_string_binary(o, 1, 3) << std::endl;);
if (m_mpz_manager.is_zero(o.significand))
mk_zero(x.ebits, x.sbits, rm == MPF_ROUND_TOWARD_NEGATIVE, o);
@ -1634,6 +1635,8 @@ std::string mpf_manager::to_string_binary(mpf const & x, unsigned upper_extra, u
"#b" + std::string(x.sbits - 1, '0') + " " +
"(" + (sgn(x) ? "-" : "+") + "zero)";
else {
SASSERT(m_mpz_manager.is_nonneg(sig(x)));
res = std::string("") + "#b" + (sgn(x) ? "1" : "0") + " ";
scoped_mpz tmp(m_mpz_manager);

13
src/util/mpf.h
View file

@ -300,6 +300,19 @@ class scoped_mpf : public _scoped_numeral<mpf_manager> {
mpf_exp_t exponent() const { return get().exponent; }
unsigned sbits() const { return get().sbits; }
void set(unsigned ebits, unsigned sbits) { get().set(ebits, sbits); }
void set(unsigned ebits, unsigned sbits, bool sign, mpf_exp_t exp, mpz & significand) {
get().set(ebits, sbits);
get().exponent = exp;
get().sign = sign;
if (&get().significand != &significand)
m().mpz_manager().set(get().significand, significand);
}
void set(unsigned ebits, unsigned sbits, bool sign, mpf_exp_t exp) {
get().set(ebits, sbits);
get().exponent = exp;
get().sign = sign;
m().mpz_manager().set(get().significand, 0);
}
public:
scoped_mpf(mpf_manager & m):_scoped_numeral<mpf_manager>(m) {}
scoped_mpf(scoped_mpf const & n):_scoped_numeral<mpf_manager>(n) {}