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FIX: avoid overflow on overflow check for Mac M1 #945

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FIX: avoid overflow on overflow check for Mac M1 #945

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73a01fc
FIX: avoid overflow on overflow check in halley_step on Apple M1
mckib2 Feb 5, 2023
9fc329a
FIX: avoid overflow on overflow check in toms748_solve safe_div
mckib2 Feb 5, 2023
c80af8e
FIX: avoid overflow on overflow check in gamma_p_derivative_imp
mckib2 Feb 5, 2023
3f76cce
FIX: avoid data-dependent overflow in halley_step
mckib2 Feb 5, 2023
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3 changes: 2 additions & 1 deletion include/boost/math/special_functions/gamma.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1795,7 +1795,8 @@ T gamma_p_derivative_imp(T a, T x, const Policy& pol)
//
typedef typename lanczos::lanczos<T, Policy>::type lanczos_type;
T f1 = detail::regularised_gamma_prefix(a, x, pol, lanczos_type());
if((x < 1) && (tools::max_value<T>() * x < f1))
static const T inv_max_value = 1.0 / tools::max_value<T>();
if((x < 1) && (x < inv_max_value * f1))
{
// overflow:
return policies::raise_overflow_error<T>("boost::math::gamma_p_derivative<%1%>(%1%, %1%)", nullptr, pol);
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11 changes: 9 additions & 2 deletions include/boost/math/tools/roots.hpp
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Expand Up @@ -354,7 +354,12 @@ namespace detail {
BOOST_MATH_INSTRUMENT_VARIABLE(denom);
BOOST_MATH_INSTRUMENT_VARIABLE(num);

if ((fabs(num) < 1) && (fabs(denom) >= fabs(num) * tools::max_value<T>()))
// denom/num overflows if:
// |denom| >= |num| * max_value
// RHS may overflow on Apple M1, so rearrange:
// |denom| * 1/max_value >= |num|
static const T inv_max_value = 1.0 / tools::max_value<T>();
if ((fabs(num) < 1) && (inv_max_value * fabs(denom) >= fabs(num)))
{
// possible overflow, use Newton step:
delta = f0 / f1;
Expand Down Expand Up @@ -647,7 +652,9 @@ namespace detail {
}
else if (result > max)
{
T diff = ((fabs(max) < 1) && (fabs(result) > 1) && (tools::max_value<T>() / fabs(result) < fabs(max))) ? T(1000) : T(result / max);
const T amax = fabs(max);
volatile const T aresult = fabs(result); // volatile: force compiler to honor data-dependency in chained bool exprs below
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You should really only need const volatile in a shared memory environment. Do you still get overflow errors with just const?

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Yes, I tried all the variations I could think of. What also worked was predclaring the amax and aresult and switching around tools::max_value<T>() / fabs(result) < fabs(max) to tools::max_value<T>() / amax < aresult, but I that was only suppressing it in this case for a specific relationship between result and max, so the volatile in my mind makes it a little more generic

T diff = ((amax < 1) && (aresult > 1) && (tools::max_value<T>() / aresult < amax)) ? T(1000) : T(result / max);
if (fabs(diff) < 1)
diff = 1 / diff;
if (!out_of_bounds_sentry && (diff > 0) && (diff < 3))
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3 changes: 2 additions & 1 deletion include/boost/math/tools/toms748_solve.hpp
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Expand Up @@ -160,7 +160,8 @@ inline T safe_div(T num, T denom, T r)

if(fabs(denom) < 1)
{
if(fabs(denom * tools::max_value<T>()) <= fabs(num))
static const T inv_max_value = 1.0 / tools::max_value<T>();
if(fabs(denom) <= inv_max_value * fabs(num))
return r;
}
return num / denom;
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