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pFq: prevent spurious overflow. #1406

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b1f70c8
pFq: prevent spurious overflow.
jzmaddock Jun 11, 2026
31b1bc1
pFq: disable one new test for real_concept.
jzmaddock Jun 11, 2026
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33 changes: 21 additions & 12 deletions include/boost/math/special_functions/detail/hypergeometric_pFq_checked_series.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@
unsigned set_crossover_locations(const Seq& aj, const Seq& bj, const Real& z, unsigned int* crossover_locations)
{
BOOST_MATH_STD_USING
using nothrow_policy = typename boost::math::policies::normalise<boost::math::policies::policy<>, boost::math::policies::rounding_error<boost::math::policies::ignore_error>>::type;
unsigned N_terms = 0;

if(aj.size() == 1 && bj.size() == 1)
Expand Down Expand Up @@ -55,13 +56,13 @@
Real t = (-sqrt(sq) - b + z) / 2;
if (t >= 0)
{
crossover_locations[N_terms] = itrunc(t);
crossover_locations[N_terms] = itrunc(t, nothrow_policy());
++N_terms;
}
t = (sqrt(sq) - b + z) / 2;
if (t >= 0)
{
crossover_locations[N_terms] = itrunc(t);
crossover_locations[N_terms] = itrunc(t, nothrow_policy());
++N_terms;
}
}
Expand All @@ -71,13 +72,13 @@
Real t = (-sqrt(sq) - b - z) / 2;
if (t >= 0)
{
crossover_locations[N_terms] = itrunc(t);
crossover_locations[N_terms] = itrunc(t, nothrow_policy());
++N_terms;
}
t = (sqrt(sq) - b - z) / 2;
if (t >= 0)
{
crossover_locations[N_terms] = itrunc(t);
crossover_locations[N_terms] = itrunc(t, nothrow_policy());
++N_terms;
}
}
Expand Down Expand Up @@ -110,7 +111,7 @@
unsigned n = 0;
for (auto bi = bj.begin(); bi != bj.end(); ++bi, ++n)
{
crossover_locations[n] = *bi >= 0 ? 0 : itrunc(-*bi) + 1;
crossover_locations[n] = *bi >= 0 ? 0 : itrunc(-*bi, nothrow_policy()) + 1;
}
std::sort(crossover_locations, crossover_locations + bj.size(), std::less<Real>());
N_terms = (unsigned)bj.size();
Expand All @@ -122,15 +123,23 @@
std::pair<Real, Real> hypergeometric_pFq_checked_series_impl(const Seq& aj, const Seq& bj, const Real& z, const Policy& pol, const Terminal& termination, long long& log_scale)
{
BOOST_MATH_STD_USING
using nothrow_policy = typename boost::math::policies::normalise<Policy, boost::math::policies::rounding_error<boost::math::policies::ignore_error>>::type;
Real result = 1;
Real abs_result = 1;
Real term = 1;
Real term0 = 0;
Real tol = boost::math::policies::get_epsilon<Real, Policy>();
std::uintmax_t k = 0;
Real upper_limit(sqrt(boost::math::tools::max_value<Real>())), diff;
if ((tools::max_value<Real>() / fabs(z) < upper_limit))
upper_limit = tools::max_value<Real>() / fabs(z);
for (auto pa = aj.begin(); pa != aj.end(); ++pa)
{
if (tools::max_value<Real>() / fabs(*pa) < upper_limit)
upper_limit = tools::max_value<Real>() / fabs(*pa);
}
Real lower_limit(1 / upper_limit);
long long log_scaling_factor = lltrunc(boost::math::tools::log_max_value<Real>()) - 2;
long long log_scaling_factor = lltrunc(boost::math::tools::log_max_value<Real>(), nothrow_policy()) - 2;
Real scaling_factor = exp(Real(log_scaling_factor));
Real term_m1;
long long local_scaling = 0;
Expand Down Expand Up @@ -234,7 +243,7 @@
log_scale += log_scaling_factor;
local_scaling += log_scaling_factor;
}
if (fabs(abs_result) < lower_limit)
else if ((fabs(abs_result) < lower_limit) && (fabs(abs_result) * scaling_factor < upper_limit))
{
abs_result *= scaling_factor;
result *= scaling_factor;
Expand Down Expand Up @@ -321,7 +330,7 @@
else
{
int ls = 1;
Real p = log_pochhammer(*ai, s, pol, &ls);
Real p = log_pochhammer(static_cast<Real>(*ai), s, pol, &ls);
s1 *= ls;
term += p;
loop_error_scale = (std::max)(p, loop_error_scale);
Expand All @@ -334,7 +343,7 @@
for (auto bi = bj.begin(); bi != bj.end(); ++bi)
{
int ls = 1;
Real p = log_pochhammer(*bi, s, pol, &ls);
Real p = log_pochhammer(static_cast<Real>(*bi), s, pol, &ls);
s2 *= ls;
term -= p;
loop_error_scale = (std::max)(p, loop_error_scale);
Expand Down Expand Up @@ -371,13 +380,13 @@
if (term <= tools::log_min_value<Real>())
{
// rescale if we can:
long long scale = lltrunc(floor(term - tools::log_min_value<Real>()) - 2);
long long scale = lltrunc(floor(term - tools::log_min_value<Real>()) - 2, nothrow_policy());
term -= scale;
loop_scale += scale;
}
if (term > 10)
{
int scale = itrunc(floor(term));
long long scale = lltrunc(floor(term), nothrow_policy());
term -= scale;
loop_scale += scale;
}
Expand All @@ -402,7 +411,7 @@
term /= scaling_factor;
loop_scale += log_scaling_factor;
}
if (fabs(loop_result) < lower_limit)
else if ((fabs(loop_result) < lower_limit) && (fabs(loop_result) * scaling_factor < upper_limit))
{
loop_result *= scaling_factor;
loop_abs_result *= scaling_factor;
Expand Down
16 changes: 13 additions & 3 deletions include/boost/math/special_functions/hypergeometric_pFq.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,12 +58,22 @@ namespace boost {
BOOST_MATH_STD_USING

long long scale = 0;
static const char* function = "boost::math::hypergeometric_pFq<%1%>(%1%,%1%,%1%)";
std::pair<value_type, value_type> r = boost::math::detail::hypergeometric_pFq_checked_series_impl(aj, bj, value_type(z), pol, boost::math::detail::iteration_terminator(boost::math::policies::get_max_series_iterations<forwarding_policy>()), scale);
r.first *= exp(Real(scale));
r.second *= exp(Real(scale));
//
// Overflow check:
//
if (static_cast<Real>(scale) > tools::log_max_value<Real>())
return (r.first < 0 ? -1 : 1) * policies::raise_overflow_error<Real, Policy>(function, nullptr, pol);
Real mul = exp(Real(scale));
if(fabs(r.first) > 1)
if(tools::max_value<Real>() / fabs(r.first) < mul)
return (r.first < 0 ? -1 : 1) * policies::raise_overflow_error<Real, Policy>(function, nullptr, pol);
r.first *= mul;
r.second *= mul;
if (p_abs_error)
*p_abs_error = static_cast<Real>(r.second) * boost::math::tools::epsilon<Real>();
return policies::checked_narrowing_cast<result_type, Policy>(r.first, "boost::math::hypergeometric_pFq<%1%>(%1%,%1%,%1%)");
return policies::checked_narrowing_cast<result_type, Policy>(r.first, function);
}

template <class Seq, class Real>
Expand Down
26 changes: 26 additions & 0 deletions test/test_pFq.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -298,6 +298,31 @@ void test_spots_2F2(T, const char*)
}
}

template <class T>
void test_special_cases(T, const char*)
{
typedef boost::math::policies::policy<boost::math::policies::overflow_error<boost::math::policies::ignore_error>> nothrow_policy;
typedef boost::math::policies::policy<boost::math::policies::overflow_error<boost::math::policies::throw_on_error>> throw_policy;
T error_rate;
BOOST_CHECK_THROW(boost::math::hypergeometric_pFq({ 2 }, { 3 }, static_cast<T>(1e10), &error_rate, throw_policy()), std::overflow_error);
BOOST_CHECK_THROW(boost::math::hypergeometric_pFq({ static_cast<T>(2) }, { static_cast<T>(3) }, static_cast<T>(1e10), &error_rate, throw_policy()), std::overflow_error);
BOOST_CHECK_THROW(boost::math::hypergeometric_pFq({ 2 }, { 3 }, boost::math::tools::max_value<T>(), &error_rate, throw_policy()), std::overflow_error);
BOOST_CHECK_THROW(boost::math::hypergeometric_pFq({ static_cast<T>(2) }, { static_cast<T>(3) }, boost::math::tools::max_value<T>(), &error_rate, throw_policy()), std::overflow_error);
BOOST_MATH_IF_CONSTEXPR(std::numeric_limits<T>::is_specialized)
{
// Can't figure out how to make this work with real_concept (we get an evaluation_error):
BOOST_CHECK_THROW(boost::math::hypergeometric_pFq({ boost::math::tools::max_value<T>() }, { static_cast<T>(3) }, static_cast<T>(0.5f), &error_rate, throw_policy()), std::overflow_error);
}
BOOST_MATH_IF_CONSTEXPR(std::numeric_limits<T>::has_infinity)
{
BOOST_CHECK_EQUAL(boost::math::hypergeometric_pFq({ 2 }, { 3 }, static_cast<T>(1e10), &error_rate, nothrow_policy()), std::numeric_limits<T>::infinity());
BOOST_CHECK_EQUAL(boost::math::hypergeometric_pFq({ static_cast<T>(2) }, { static_cast<T>(3) }, static_cast<T>(1e10), &error_rate, nothrow_policy()), std::numeric_limits<T>::infinity());
BOOST_CHECK_EQUAL(boost::math::hypergeometric_pFq({ 2 }, { 3 }, boost::math::tools::max_value<T>(), &error_rate, nothrow_policy()), std::numeric_limits<T>::infinity());
BOOST_CHECK_EQUAL(boost::math::hypergeometric_pFq({ static_cast<T>(2) }, { static_cast<T>(3) }, boost::math::tools::max_value<T>(), &error_rate, nothrow_policy()), std::numeric_limits<T>::infinity());
BOOST_CHECK_EQUAL(boost::math::hypergeometric_pFq({ boost::math::tools::max_value<T>() }, { static_cast<T>(3) }, static_cast<T>(0.5f), &error_rate, nothrow_policy()), std::numeric_limits<T>::infinity());
}
}

template <class T>
void test_spots(T z, const char* type_name)
{
Expand All @@ -309,4 +334,5 @@ void test_spots(T z, const char* type_name)
test_spots_1F2(z, type_name);
test_spots_2F2(z, type_name);
test_spots_2F1(z, type_name);
test_special_cases(z, type_name);
}
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