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Fixed renormalization in fp.fma. Relates to #872.

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This commit is contained in:
Christoph M. Wintersteiger 2017-07-28 23:01:01 +01:00
parent e677030b74
commit 175f042db8
2 changed files with 27 additions and 1 deletions
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11
src/util/mpf.cpp
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@ -902,6 +902,7 @@ void mpf_manager::fma(mpf_rounding_mode rm, mpf const & x, mpf const & y, mpf co
TRACE("mpf_dbg", tout << "S'= " << m_mpz_manager.to_string(res.significand()) << std::endl;
tout << "S'= " << to_string_binary(res, 1, 0) << std::endl; );
// Renormalize
bool renorm_sticky = false;
SASSERT(m_mpz_manager.lt(res.significand(), m_powers2(2 * x.sbits + 1)));
@ -916,6 +917,16 @@ void mpf_manager::fma(mpf_rounding_mode rm, mpf const & x, mpf const & y, mpf co
tout << "S*= " << to_string_binary(res, 2, 0) << std::endl;);
}
mpf_exp_t min_exp = mk_min_exp(x.ebits);
unsigned sig_width = m_mpz_manager.prev_power_of_two(res.get().significand) + 1;
mpf_exp_t sig_lz = 2 * x.sbits - sig_width; // want << lz
mpf_exp_t max_exp_delta = res.exponent() - min_exp;
unsigned renorm_delta = (unsigned) std::max((mpf_exp_t)0, std::min(sig_lz, max_exp_delta));
res.get().exponent -= renorm_delta;
m_mpz_manager.mul2k(res.significand(), renorm_delta);
TRACE("mpf_dbg", tout << "R*= " << to_string_binary(res, 2, 0) << " (renormalized, delta=" << renorm_delta << ")" << std::endl;);
set(o, x.ebits, x.sbits, res.sign(), res.exponent(), mpz(0));
if (x.sbits >= 4) {