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operator bool() and set_zero(): test for zero and set to zero respectively. #39

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Merged
jzmaddock merged 6 commits into from
May 26, 2016
Merged

operator bool() and set_zero(): test for zero and set to zero respectively. #39

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a737a3f
operator bool() and clear(): test for zero and set to zero respectively.
jeremy-murphy May 11, 2016
18a4986
Use typedef hack to prevent accidental conversion to an arithmetic type.
jeremy-murphy May 12, 2016
e608dc6
Rename clear() to set_zero().
jeremy-murphy May 13, 2016
0fd22d7
polynomial: Example documentation for test/set zero.
jeremy-murphy May 15, 2016
94526e5
Merge branch 'develop' into polynomial_zero
jeremy-murphy May 15, 2016
9558b22
Update API documentation.
jeremy-murphy May 15, 2016
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27 changes: 19 additions & 8 deletions include/boost/math/tools/polynomial.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -191,8 +191,8 @@ std::pair< polynomial<T>, polynomial<T> >
division(polynomial<T> u, const polynomial<T>& v)
{
BOOST_ASSERT(v.size() <= u.size());
BOOST_ASSERT(v != zero_element(std::multiplies< polynomial<T> >()));
BOOST_ASSERT(u != zero_element(std::multiplies< polynomial<T> >()));
BOOST_ASSERT(v);
BOOST_ASSERT(u);

typedef typename polynomial<T>::size_type N;

Expand Down Expand Up @@ -245,9 +245,9 @@ template <typename T>
std::pair< polynomial<T>, polynomial<T> >
quotient_remainder(const polynomial<T>& dividend, const polynomial<T>& divisor)
{
BOOST_ASSERT(divisor != zero_element(std::multiplies< polynomial<T> >()));
BOOST_ASSERT(divisor);
if (dividend.size() < divisor.size())
return std::make_pair(zero_element(std::multiplies< polynomial<T> >()), dividend);
return std::make_pair(polynomial<T>(), dividend);
return detail::division(dividend, divisor);
}

Expand Down Expand Up @@ -389,7 +389,7 @@ class polynomial :
polynomial& operator %=(const U& /*value*/)
{
// We can always divide by a scalar, so there is no remainder:
*this = zero_element(std::multiplies<polynomial>());
this->clear();
return *this;
}

Expand All @@ -412,10 +412,9 @@ class polynomial :
polynomial& operator *=(const polynomial<U>& value)
{
// TODO: FIXME: use O(N log(N)) algorithm!!!
polynomial const zero = zero_element(std::multiplies<polynomial>());
if (value == zero)
if (!value)
{
*this = zero;
this->clear();
return *this;
}
std::vector<T> prod(size() + value.size() - 1, T(0));
Expand Down Expand Up @@ -455,6 +454,18 @@ class polynomial :
normalize();
return *this;
}

// Useful for fast test of equality to zero.
operator bool() const

@jzmaddock jzmaddock May 11, 2016

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This should be explicit when BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS is not set, otherwise use an implicit conversion to an "unmentionable" type, for example multiprecision::number uses:

typedef bool (self_type::*unmentionable_type)()const;

BOOST_MP_FORCEINLINE operator unmentionable_type()const
{
return is_zero() ? 0 : &self_type::is_zero;
}

Which prevents accidental conversion to an arithmetic type.

@jeremy-murphy jeremy-murphy May 12, 2016

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Ahh, wow, that's a new one on me. What about naming a function that sets the polynomial to zero? I have used the verb clear but maybe set_zero is more appropriate? This is on the assumption that it is more efficient than assignment from zero, which I assume the compiler is not quite smart enough to optimize away for a class such as polynomial.

@jzmaddock jzmaddock May 12, 2016

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On 12/05/2016 12:08, Jeremy W. Murphy wrote:

In include/boost/math/tools/polynomial.hpp
#39 (comment):

@@ -455,6 +454,18 @@ class polynomial :
normalize();
return *this;
}
+

  • // Useful for fast test of equality to zero.
  • operator bool() const

Ahh, wow, that's a new one on me. What about naming a function that
sets the polynomial to zero? I have used the verb |clear| but maybe
|set_zero| is more appropriate? This is on the assumption that it is
more efficient than assignment from zero, which I assume the compiler
is not quite smart enough to optimize away for a class such as polynomial.

clear() works for me.

{
return !m_data.empty();
}

// Fast way to set a polynomial to zero.
void clear()
{
m_data.clear();
}

/** Remove zero coefficients 'from the top', that is for which there are no
* non-zero coefficients of higher degree. */
Expand Down
18 changes: 18 additions & 0 deletions test/test_polynomial.cpp
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Expand Up @@ -298,3 +298,21 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(test_odd_even, T, all_test_types)
BOOST_CHECK_EQUAL(odd(b), false);
BOOST_CHECK_EQUAL(even(b), true);
}


BOOST_AUTO_TEST_CASE_TEMPLATE(test_bool, T, all_test_types)
{
polynomial<T> const zero;
polynomial<T> const a(d0a.begin(), d0a.end());
BOOST_CHECK_EQUAL(bool(zero), false);
BOOST_CHECK_EQUAL(bool(a), true);
}


BOOST_AUTO_TEST_CASE_TEMPLATE(test_clear, T, all_test_types)
{
polynomial<T> const zero;
polynomial<T> a(d0a.begin(), d0a.end());
a.clear();
BOOST_CHECK_EQUAL(a, zero);
}