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Merge pull request #600 from wintersteiger/new-mpf-rem

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New mpf_manager::rem
This commit is contained in:
Christoph M. Wintersteiger 2016-05-12 14:16:53 +01:00
parent d4f3ea99da dd83495d5d
commit 37f4cc89c9
2 changed files with 233 additions and 47 deletions
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269
src/util/mpf.cpp
View file

@ -1214,11 +1214,202 @@ void mpf_manager::to_ieee_bv_mpz(const mpf & x, scoped_mpz & o) {
}
}
void mpf_manager::renormalize(unsigned ebits, unsigned sbits, mpf_exp_t & exp, mpz & sig) {
if (m_mpz_manager.is_zero(sig))
return;
mpf_exp_t max_e = mk_max_exp(ebits);
mpf_exp_t min_e = mk_min_exp(ebits);
const mpz & pg = m_powers2(sbits);
while (m_mpz_manager.ge(sig, pg)) {
m_mpz_manager.machine_div2k(sig, 1);
exp++;
}
const mpz & pl = m_powers2(sbits-1);
while (m_mpz_manager.lt(sig, pl)) {
m_mpz_manager.mul2k(sig, 1);
exp--;
}
}
void mpf_manager::partial_remainder(scoped_mpf & x, scoped_mpf const & y, mpf_exp_t const & exp_diff, bool partial) {
unsigned ebits = x.get().ebits;
unsigned sbits = x.get().sbits;
bool sign = x.get().sign;
SASSERT(-1 <= exp_diff && exp_diff < INT64_MAX);
SASSERT(exp_diff < ebits+sbits || partial);
signed int D = (signed int)(exp_diff);
mpf_exp_t N = (sbits+ebits)/2;
TRACE("mpf_dbg_rem", tout << "x=" << to_string(x) << std::endl;
tout << "y=" << to_string(y) << std::endl;
tout << "d=" << D << std::endl;
tout << "partial=" << partial << std::endl;);
SASSERT(m_mpz_manager.lt(x.significand(), m_powers2(sbits)));
SASSERT(m_mpz_manager.ge(x.significand(), m_powers2(sbits - 1)));
SASSERT(m_mpz_manager.lt(y.significand(), m_powers2(sbits)));
SASSERT(m_mpz_manager.ge(y.significand(), m_powers2(sbits - 1)));
// 1. Compute a/b
bool x_div_y_sgn = x.sign() ^ y.sign();
mpf_exp_t x_div_y_exp = D;
scoped_mpz x_sig_shifted(m_mpz_manager), x_div_y_sig_lrg(m_mpz_manager), x_div_y_rem(m_mpz_manager);
scoped_mpz x_rem_y_sig(m_mpz_manager);
m_mpz_manager.mul2k(x.significand(), 2*sbits + 2, x_sig_shifted);
m_mpz_manager.machine_div_rem(x_sig_shifted, y.significand(), x_div_y_sig_lrg, x_div_y_rem); // rem useful?
// x/y is in x_diuv_y_sig_lrg and has sbits+3 extra bits.
TRACE("mpf_dbg_rem", tout << "X/Y_exp=" << x_div_y_exp << std::endl;
tout << "X/Y_sig_lrg=" << m_mpz_manager.to_string(x_div_y_sig_lrg) << std::endl;
tout << "X/Y_rem=" << m_mpz_manager.to_string(x_div_y_rem) << std::endl;
scoped_mpf & XdY = to_packed_mpf(x_div_y_sgn, x_div_y_exp, x_div_y_sig_lrg, ebits, sbits, sbits+3);
tout << "X/Y~=" << to_string_hexfloat(XdY) << std::endl;);
// 2. Round a/b to integer Q/QQ
bool Q_sgn = x_div_y_sgn;
mpf_exp_t Q_exp = x_div_y_exp;
scoped_mpz Q_sig(m_mpz_manager), Q_rem(m_mpz_manager);
unsigned Q_shft = (sbits-1) + (sbits+3) - (unsigned) (partial ? N :Q_exp);
if (partial) {
// Round according to MPF_ROUND_TOWARD_ZERO
SASSERT(0 < N && N < Q_exp && Q_exp < INT_MAX);
m_mpz_manager.machine_div2k(x_div_y_sig_lrg, Q_shft, Q_sig);
}
else {
// Round according to MPF_ROUND_NEAREST_TEVEN
m_mpz_manager.machine_div_rem(x_div_y_sig_lrg, m_powers2(Q_shft), Q_sig, Q_rem);
const mpz & shiftm1_p = m_powers2(Q_shft-1);
bool tie = m_mpz_manager.eq(Q_rem, shiftm1_p);
bool more_than_tie = m_mpz_manager.gt(Q_rem, shiftm1_p);
TRACE("mpf_dbg_rem", tout << "tie= " << tie << "; >tie= " << more_than_tie << std::endl;);
if ((tie && m_mpz_manager.is_odd(Q_sig)) || more_than_tie)
m_mpz_manager.inc(Q_sig);
}
m_mpz_manager.mul2k(Q_sig, Q_shft);
m_mpz_manager.machine_div2k(Q_sig, sbits+3);
renormalize(ebits, sbits, Q_exp, Q_sig);
TRACE("mpf_dbg_rem", tout << "Q_exp=" << Q_exp << std::endl;
tout << "Q_sig=" << m_mpz_manager.to_string(Q_sig) << std::endl;
scoped_mpf & Q = to_packed_mpf(Q_sgn, Q_exp, Q_sig, ebits, sbits, 0);
tout << "Q=" << to_string_hexfloat(Q) << std::endl;);
if ((D == -1 || partial) && m_mpz_manager.is_zero(Q_sig))
return; // This means x % y = x.
// no extra bits in Q_sig.
SASSERT(!m_mpz_manager.is_zero(Q_sig));
SASSERT(m_mpz_manager.lt(Q_sig, m_powers2(sbits)));
SASSERT(m_mpz_manager.ge(Q_sig, m_powers2(sbits - 1)));
// 3. Compute Y*Q / Y*QQ*2^{D-N}
bool YQ_sgn = y.sign() ^ Q_sgn;
scoped_mpz YQ_sig(m_mpz_manager);
mpf_exp_t YQ_exp = Q_exp + y.exponent();
m_mpz_manager.mul(y.significand(), Q_sig, YQ_sig);
renormalize(ebits, 2*sbits-1, YQ_exp, YQ_sig); // YQ_sig has `sbits-1' extra bits.
TRACE("mpf_dbg_rem", tout << "YQ_sgn=" << YQ_sgn << std::endl;
tout << "YQ_exp=" << YQ_exp << std::endl;
tout << "YQ_sig=" << m_mpz_manager.to_string(YQ_sig) << std::endl;
scoped_mpf & YQ = to_packed_mpf(YQ_sgn, YQ_exp, YQ_sig, ebits, sbits, sbits-1);
tout << "YQ=" << to_string_hexfloat(YQ) << std::endl;);
// `sbits-1' extra bits in YQ_sig.
SASSERT(m_mpz_manager.lt(YQ_sig, m_powers2(2*sbits-1)));
SASSERT(m_mpz_manager.ge(YQ_sig, m_powers2(2*sbits-2)) || YQ_exp <= mk_bot_exp(ebits));
// 4. Compute X-Y*Q
mpf_exp_t X_YQ_exp = x.exponent();
scoped_mpz X_YQ_sig(m_mpz_manager);
mpf_exp_t exp_delta = exp(x) - YQ_exp;
TRACE("mpf_dbg_rem", tout << "exp_delta=" << exp_delta << std::endl;);
SASSERT(INT_MIN < exp_delta && exp_delta <= INT_MAX);
scoped_mpz minuend(m_mpz_manager), subtrahend(m_mpz_manager);
scoped_mpz x_sig_lrg(m_mpz_manager);
m_mpz_manager.mul2k(x.significand(), sbits-1, x_sig_lrg); // sbits-1 extra bits into x
m_mpz_manager.set(minuend, x_sig_lrg);
m_mpz_manager.set(subtrahend, YQ_sig);
SASSERT(m_mpz_manager.lt(minuend, m_powers2(2*sbits-1)));
SASSERT(m_mpz_manager.ge(minuend, m_powers2(2*sbits-2)));
SASSERT(m_mpz_manager.lt(subtrahend, m_powers2(2*sbits-1)));
SASSERT(m_mpz_manager.ge(subtrahend, m_powers2(2*sbits-2)));
if (exp_delta != 0) {
scoped_mpz sticky_rem(m_mpz_manager);
m_mpz_manager.set(sticky_rem, 0);
if (exp_delta > sbits+5)
sticky_rem.swap(subtrahend);
else if (exp_delta > 0)
m_mpz_manager.machine_div_rem(subtrahend, m_powers2((unsigned)exp_delta), subtrahend, sticky_rem);
else {
SASSERT(exp_delta < 0);
exp_delta = -exp_delta;
m_mpz_manager.mul2k(subtrahend, (int)exp_delta);
}
if (!m_mpz_manager.is_zero(sticky_rem) && m_mpz_manager.is_even(subtrahend))
m_mpz_manager.inc(subtrahend);
TRACE("mpf_dbg_rem", tout << "aligned subtrahend=" << m_mpz_manager.to_string(subtrahend) << std::endl;);
}
m_mpz_manager.sub(minuend, subtrahend, X_YQ_sig);
TRACE("mpf_dbg_rem", tout << "X_YQ_sig'=" << m_mpz_manager.to_string(X_YQ_sig) << std::endl;);
bool neg = m_mpz_manager.is_neg(X_YQ_sig);
if (neg) m_mpz_manager.neg(X_YQ_sig);
bool X_YQ_sgn = ((!x.sign() && !YQ_sgn && neg) ||
(x.sign() && YQ_sgn && !neg) ||
(x.sign() && !YQ_sgn));
// 5. Rounding
if (m_mpz_manager.is_zero(X_YQ_sig))
mk_zero(ebits, sbits, x.sign(), x);
else {
renormalize(ebits, 2*sbits-1, X_YQ_exp, X_YQ_sig);
TRACE("mpf_dbg_rem", tout << "minuend=" << m_mpz_manager.to_string(minuend) << std::endl;
tout << "subtrahend=" << m_mpz_manager.to_string(subtrahend) << std::endl;
tout << "X_YQ_sgn=" << X_YQ_sgn << std::endl;
tout << "X_YQ_exp=" << X_YQ_exp << std::endl;
tout << "X_YQ_sig=" << m_mpz_manager.to_string(X_YQ_sig) << std::endl;
scoped_mpf & X_YQ = to_packed_mpf(X_YQ_sgn, X_YQ_exp, X_YQ_sig, ebits, sbits, sbits-1);
tout << "X-YQ=" << to_string_hexfloat(X_YQ) << std::endl;);
// `sbits-1' extra bits in X_YQ_sig
SASSERT(m_mpz_manager.lt(X_YQ_sig, m_powers2(2*sbits-1)));
scoped_mpz rnd_bits(m_mpz_manager);
m_mpz_manager.machine_div_rem(X_YQ_sig, m_powers2(sbits-1), X_YQ_sig, rnd_bits);
TRACE("mpf_dbg_rem", tout << "final sticky=" << m_mpz_manager.to_string(rnd_bits) << std::endl; );
// Round to nearest, ties to even.
if (m_mpz_manager.eq(rnd_bits, mpz(32))) { // tie.
if (m_mpz_manager.is_odd(X_YQ_sig)) {
m_mpz_manager.inc(X_YQ_sig);
}
}
else if (m_mpz_manager.gt(rnd_bits, mpz(32)))
m_mpz_manager.inc(X_YQ_sig);
set(x, ebits, sbits, X_YQ_sgn, X_YQ_exp, X_YQ_sig);
}
TRACE("mpf_dbg_rem", tout << "partial remainder = " << to_string_hexfloat(x) << std::endl;);
}
void mpf_manager::rem(mpf const & x, mpf const & y, mpf & o) {
SASSERT(x.sbits == y.sbits && x.ebits == y.ebits);
TRACE("mpf_dbg", tout << "X = " << to_string(x) << std::endl;);
TRACE("mpf_dbg", tout << "Y = " << to_string(y) << std::endl;);
TRACE("mpf_dbg_rem", tout << "X = " << to_string(x) << "=" << to_string_hexfloat(x) << std::endl;
tout << "Y = " << to_string(y) << "=" << to_string_hexfloat(y) << std::endl;);
if (is_nan(x) || is_nan(y))
mk_nan(x.ebits, x.sbits, o);
@ -1231,58 +1422,35 @@ void mpf_manager::rem(mpf const & x, mpf const & y, mpf & o) {
else if (is_zero(x))
set(o, x);
else {
// This is a generalized version of the algorithm for FPREM1 in the Intel
SASSERT(is_regular(x) && is_regular(y));
// This is a generalized version of the algorithm for FPREM1 in the `Intel
// 64 and IA-32 Architectures Software Developer's Manual',
// Section 3-402 Vol. 2A FPREM1-Partial Remainder'.
// Section 3-402 Vol. 2A `FPREM1-Partial Remainder'.
scoped_mpf ST0(*this), ST1(*this);
set(ST0, x);
set(ST1, y);
unpack(ST0, true);
unpack(ST1, true);
const mpf_exp_t B = x.sbits-1; // max bits per iteration.
const mpf_exp_t B = x.sbits+x.ebits;
mpf_exp_t D;
do {
D = ST0.exponent() - ST1.exponent();
TRACE("mpf_dbg_rem", tout << "st0=" << to_string_hexfloat(ST0) << std::endl;
tout << "st1=" << to_string_hexfloat(ST1) << std::endl;
tout << "D=" << D << std::endl;);
if (D < B) {
scoped_mpf ST0_DIV_ST1(*this), Q(*this), ST1_MUL_Q(*this), ST0p(*this);
div(MPF_ROUND_NEAREST_TEVEN, ST0, ST1, ST0_DIV_ST1);
round_to_integral(MPF_ROUND_NEAREST_TEVEN, ST0_DIV_ST1, Q);
mul(MPF_ROUND_NEAREST_TEVEN, ST1, Q, ST1_MUL_Q);
sub(MPF_ROUND_NEAREST_TEVEN, ST0, ST1_MUL_Q, ST0p);
TRACE("mpf_dbg_rem", tout << "ST0/ST1=" << to_string_hexfloat(ST0_DIV_ST1) << std::endl;
tout << "Q=" << to_string_hexfloat(Q) << std::endl;
tout << "ST1*Q=" << to_string_hexfloat(ST1_MUL_Q) << std::endl;
tout << "ST0'=" << to_string_hexfloat(ST0p) << std::endl;);
set(ST0, ST0p);
if (ST0.exponent() < (ST1.exponent()) - 1) {
D = 0;
}
else {
const mpf_exp_t N = B;
scoped_mpf ST0_DIV_ST1(*this), QQ(*this), ST1_MUL_QQ(*this), ST0p(*this);
div(MPF_ROUND_TOWARD_ZERO, ST0, ST1, ST0_DIV_ST1);
ST0_DIV_ST1.get().exponent -= D - N;
round_to_integral(MPF_ROUND_TOWARD_ZERO, ST0_DIV_ST1, QQ);
mul(MPF_ROUND_NEAREST_TEVEN, ST1, QQ, ST1_MUL_QQ);
ST1_MUL_QQ.get().exponent += D - N;
sub(MPF_ROUND_NEAREST_TEVEN, ST0, ST1_MUL_QQ, ST0p);
TRACE("mpf_dbg_rem", tout << "ST0/ST1/2^{D-N}=" << to_string_hexfloat(ST0_DIV_ST1) << std::endl;
tout << "QQ=" << to_string_hexfloat(QQ) << std::endl;
tout << "ST1*QQ*2^{D-N}=" << to_string_hexfloat(ST1_MUL_QQ) << std::endl;
tout << "ST0'=" << to_string_hexfloat(ST0p) << std::endl;);
SASSERT(!eq(ST0, ST0p));
set(ST0, ST0p);
D = ST0.exponent() - ST1.exponent();
partial_remainder(ST0, ST1, D, (D >= B));
}
} while (D >= B && !ST0.is_zero());
SASSERT(ST0.exponent() - ST1.exponent() <= D);
} while (D >= B);
set(o, ST0);
if (is_zero(o))
o.sign = x.sign;
m_mpz_manager.mul2k(ST0.significand(), 3);
set(o, x.ebits, x.sbits, MPF_ROUND_TOWARD_ZERO, ST0);
round(MPF_ROUND_NEAREST_TEVEN, o);
}
TRACE("mpf_dbg_rem", tout << "R = " << to_string(o) << "=" << to_string_hexfloat(o) << std::endl; );
TRACE("mpf_dbg", tout << "REMAINDER = " << to_string(o) << std::endl;);
}
@ -1364,9 +1532,9 @@ std::string mpf_manager::to_string(mpf const & x) {
}
}
//DEBUG_CODE(
// res += " " + to_string_hexfloat(x);
//);
DEBUG_CODE(
res += " " + to_string_raw(x);
);
return res;
}
@ -1407,6 +1575,19 @@ std::string mpf_manager::to_string_raw(mpf const & x) {
return res;
}
scoped_mpf mpf_manager::to_packed_mpf(bool sgn, mpf_exp_t exp, scoped_mpz const & sig, unsigned ebits, unsigned sbits, unsigned rbits) {
scoped_mpf q(*this);
scoped_mpz q_sig(m_mpz_manager);
m_mpz_manager.set(q_sig, sig);
if (rbits != 0) m_mpz_manager.div(q_sig, m_powers2(rbits), q_sig); // restore scale
if (m_mpz_manager.ge(q_sig, m_powers2(sbits-1)))
m_mpz_manager.sub(q_sig, m_powers2(sbits-1), q_sig); // strip hidden bit
else if (exp == mk_min_exp(ebits))
exp = mk_bot_exp(ebits);
set(q, ebits, sbits, sgn, exp, q_sig);
return q;
}
std::string mpf_manager::to_string_hexfloat(mpf const & x) {
std::stringstream ss("");
std::ios::fmtflags ff = ss.setf(std::ios_base::hex | std::ios_base::uppercase |

11
src/util/mpf.h
View file

@ -185,9 +185,6 @@ public:
void mk_pinf(unsigned ebits, unsigned sbits, mpf & o);
void mk_ninf(unsigned ebits, unsigned sbits, mpf & o);
std::string to_string_raw(mpf const & a);
std::string to_string_hexfloat(mpf const & a);
unsynch_mpz_manager & mpz_manager(void) { return m_mpz_manager; }
unsynch_mpq_manager & mpq_manager(void) { return m_mpq_manager; }
@ -226,6 +223,9 @@ protected:
void round(mpf_rounding_mode rm, mpf & o);
void round_sqrt(mpf_rounding_mode rm, mpf & o);
void renormalize(unsigned ebits, unsigned sbits, mpf_exp_t & exp, mpz & sig);
void partial_remainder(scoped_mpf & x, scoped_mpf const & y, mpf_exp_t const & exp_diff, bool partial);
void mk_round_inf(mpf_rounding_mode rm, mpf & o);
// Convert x into a mpz numeral. zm is the manager that owns o.
@ -284,6 +284,10 @@ protected:
}
};
std::string to_string_raw(mpf const & a);
std::string to_string_hexfloat(mpf const & a);
scoped_mpf to_packed_mpf(bool sgn, mpf_exp_t exp, scoped_mpz const & sig, unsigned ebits, unsigned sbits, unsigned rbits);
public:
powers2 m_powers2;
};
@ -291,6 +295,7 @@ public:
class scoped_mpf : public _scoped_numeral<mpf_manager> {
friend class mpf_manager;
mpz & significand() { return get().significand; }
const mpz & significand() const { return get().significand; }
bool sign() const { return get().sign; }
mpf_exp_t exponent() const { return get().exponent; }
unsigned sbits() const { return get().sbits; }