void eval_exp(T& result, const T& x)
{
BOOST_STATIC_ASSERT_MSG(number_category<T>::value == number_kind_floating_point, "The exp function is only valid for floating point types.");
if(&x == &result)
{
T temp;
eval_exp(temp, x);
result = temp;
return;
}
typedef typename boost::multiprecision::detail::canonical<unsigned, T>::type ui_type;
typedef typename boost::multiprecision::detail::canonical<int, T>::type si_type;
typedef typename T::exponent_type exp_type;
typedef typename boost::multiprecision::detail::canonical<exp_type, T>::type canonical_exp_type;
typedef typename boost::multiprecision::detail::canonical<float, T>::type float_type;
// Handle special arguments.
int type = eval_fpclassify(x);
bool isneg = eval_get_sign(x) < 0;
if(type == FP_NAN)
{
result = std::numeric_limits<number<T, et_on> >::quiet_NaN().backend();
return;
}
else if(type == FP_INFINITE)
{
result = x;
if(isneg)
result = ui_type(0u);
else
result = x;
return;
}
else if(type == FP_ZERO)
{
result = ui_type(1);
return;
}
// Get local copy of argument and force it to be positive.
T xx = x;
T exp_series;
if(isneg)
xx.negate();
// Check the range of the argument.
static const canonical_exp_type maximum_arg_for_exp = std::numeric_limits<number<T, et_on> >::max_exponent == 0 ? (std::numeric_limits<long>::max)() : std::numeric_limits<number<T, et_on> >::max_exponent;
if(xx.compare(maximum_arg_for_exp) >= 0)
{
// Overflow / underflow
if(isneg)
result = ui_type(0);
else
result = std::numeric_limits<number<T, et_on> >::has_infinity ? std::numeric_limits<number<T, et_on> >::infinity().backend() : (std::numeric_limits<number<T, et_on> >::max)().backend();
return;
}
if(xx.compare(si_type(1)) <= 0)
{
//
// Use series for exp(x) - 1:
//
T lim = std::numeric_limits<number<T, et_on> >::epsilon().backend();
unsigned k = 2;
exp_series = xx;
result = si_type(1);
if(isneg)
eval_subtract(result, exp_series);
else
eval_add(result, exp_series);
eval_multiply(exp_series, xx);
eval_divide(exp_series, ui_type(k));
eval_add(result, exp_series);
while(exp_series.compare(lim) > 0)
{
++k;
eval_multiply(exp_series, xx);
eval_divide(exp_series, ui_type(k));
if(isneg && (k&1))
eval_subtract(result, exp_series);
else
eval_add(result, exp_series);
}
return;
}
// Check for pure-integer arguments which can be either signed or unsigned.
typename boost::multiprecision::detail::canonical<boost::intmax_t, T>::type ll;
eval_trunc(exp_series, x);
eval_convert_to(&ll, exp_series);
if(x.compare(ll) == 0)
{
detail::pow_imp(result, get_constant_e<T>(), ll, mpl::true_());
return;
}
// The algorithm for exp has been taken from MPFUN.
// exp(t) = [ (1 + r + r^2/2! + r^3/3! + r^4/4! ...)^p2 ] * 2^n
// where p2 is a power of 2 such as 2048, r = t_prime / p2, and
// t_prime = t - n*ln2, with n chosen to minimize the absolute
// value of t_prime. In the resulting Taylor series, which is
// implemented as a hypergeometric function, |r| is bounded by
// ln2 / p2. For small arguments, no scaling is done.
// Compute the exponential series of the (possibly) scaled argument.
eval_divide(result, xx, get_constant_ln2<T>());
exp_type n;
eval_convert_to(&n, result);
// The scaling is 2^11 = 2048.
static const si_type p2 = static_cast<si_type>(si_type(1) << 11);
eval_multiply(exp_series, get_constant_ln2<T>(), static_cast<canonical_exp_type>(n));
eval_subtract(exp_series, xx);
eval_divide(exp_series, p2);
exp_series.negate();
hyp0F0(result, exp_series);
detail::pow_imp(exp_series, result, p2, mpl::true_());
result = ui_type(1);
eval_ldexp(result, result, n);
eval_multiply(exp_series, result);
if(isneg)
eval_divide(result, ui_type(1), exp_series);
else
result = exp_series;
}
inline void eval_pow(T& result, const T& x, const T& a)
{
BOOST_STATIC_ASSERT_MSG(number_category<T>::value == number_kind_floating_point, "The pow function is only valid for floating point types.");
typedef typename boost::multiprecision::detail::canonical<int, T>::type si_type;
typedef typename boost::multiprecision::detail::canonical<unsigned, T>::type ui_type;
typedef typename T::exponent_type exp_type;
typedef typename boost::multiprecision::detail::canonical<exp_type, T>::type canonical_exp_type;
typedef typename mpl::front<typename T::float_types>::type fp_type;
if((&result == &x) || (&result == &a))
{
T t;
eval_pow(t, x, a);
result = t;
return;
}
if(a.compare(si_type(1)) == 0)
{
result = x;
return;
}
int type = eval_fpclassify(x);
switch(type)
{
case FP_INFINITE:
result = x;
return;
case FP_ZERO:
result = si_type(1);
return;
case FP_NAN:
result = x;
return;
default: ;
}
if(eval_get_sign(a) == 0)
{
result = si_type(1);
return;
}
if(a.compare(si_type(-1)) < 0)
{
T t, da;
t = a;
t.negate();
eval_pow(da, x, t);
eval_divide(result, si_type(1), da);
return;
}
bool bo_a_isint = false;
typename boost::multiprecision::detail::canonical<boost::intmax_t, T>::type an;
T fa;
try
{
eval_convert_to(&an, a);
if(a.compare(an) == 0)
{
detail::pow_imp(result, x, an, mpl::true_());
return;
}
}
catch(const std::exception&)
{
// conversion failed, just fall through, value is not an integer.
an = (std::numeric_limits<boost::intmax_t>::max)();
}
if((eval_get_sign(x) < 0) && !bo_a_isint)
{
result = std::numeric_limits<number<T, et_on> >::quiet_NaN().backend();
}
T t, da;
eval_subtract(da, a, an);
if((x.compare(fp_type(0.5)) >= 0) && (x.compare(fp_type(0.9)) < 0))
{
if(a.compare(fp_type(1e-5f)) <= 0)
{
// Series expansion for small a.
eval_log(t, x);
eval_multiply(t, a);
hyp0F0(result, t);
return;
}
else
{
// Series expansion for moderately sized x. Note that for large power of a,
// the power of the integer part of a is calculated using the pown function.
if(an)
{
da.negate();
t = si_type(1);
eval_subtract(t, x);
hyp1F0(result, da, t);
detail::pow_imp(t, x, an, mpl::true_());
eval_multiply(result, t);
}
else
{
da = a;
da.negate();
t = si_type(1);
eval_subtract(t, x);
hyp1F0(result, da, t);
}
}
}
else
{
// Series expansion for pow(x, a). Note that for large power of a, the power
// of the integer part of a is calculated using the pown function.
if(an)
{
eval_log(t, x);
eval_multiply(t, da);
eval_exp(result, t);
detail::pow_imp(t, x, an, mpl::true_());
eval_multiply(result, t);
}
else
{
eval_log(t, x);
eval_multiply(t, a);
eval_exp(result, t);
}
}
}
inline void eval_pow(T& result, const T& x, const T& a)
{
BOOST_STATIC_ASSERT_MSG(number_category<T>::value == number_kind_floating_point, "The pow function is only valid for floating point types.");
typedef typename boost::multiprecision::detail::canonical<int, T>::type si_type;
typedef typename mpl::front<typename T::float_types>::type fp_type;
if((&result == &x) || (&result == &a))
{
T t;
eval_pow(t, x, a);
result = t;
return;
}
if(a.compare(si_type(1)) == 0)
{
result = x;
return;
}
int type = eval_fpclassify(x);
switch(type)
{
case FP_INFINITE:
result = x;
return;
case FP_ZERO:
switch(eval_fpclassify(a))
{
case FP_ZERO:
result = si_type(1);
break;
case FP_NAN:
result = a;
break;
default:
result = x;
break;
}
return;
case FP_NAN:
result = x;
return;
default: ;
}
int s = eval_get_sign(a);
if(s == 0)
{
result = si_type(1);
return;
}
if(s < 0)
{
T t, da;
t = a;
t.negate();
eval_pow(da, x, t);
eval_divide(result, si_type(1), da);
return;
}
typename boost::multiprecision::detail::canonical<boost::intmax_t, T>::type an;
T fa;
#ifndef BOOST_NO_EXCEPTIONS
try
{
#endif
eval_convert_to(&an, a);
if(a.compare(an) == 0)
{
detail::pow_imp(result, x, an, mpl::true_());
return;
}
#ifndef BOOST_NO_EXCEPTIONS
}
catch(const std::exception&)
{
// conversion failed, just fall through, value is not an integer.
an = (std::numeric_limits<boost::intmax_t>::max)();
}
#endif
if((eval_get_sign(x) < 0))
{
typename boost::multiprecision::detail::canonical<boost::uintmax_t, T>::type aun;
#ifndef BOOST_NO_EXCEPTIONS
try
{
#endif
eval_convert_to(&aun, a);
if(a.compare(aun) == 0)
{
fa = x;
fa.negate();
eval_pow(result, fa, a);
if(aun & 1u)
result.negate();
return;
}
#ifndef BOOST_NO_EXCEPTIONS
}
catch(const std::exception&)
{
// conversion failed, just fall through, value is not an integer.
}
#endif
if(std::numeric_limits<number<T, et_on> >::has_quiet_NaN)
result = std::numeric_limits<number<T, et_on> >::quiet_NaN().backend();
else
{
BOOST_THROW_EXCEPTION(std::domain_error("Result of pow is undefined or non-real and there is no NaN for this number type."));
}
return;
}
T t, da;
eval_subtract(da, a, an);
if((x.compare(fp_type(0.5)) >= 0) && (x.compare(fp_type(0.9)) < 0))
{
if(a.compare(fp_type(1e-5f)) <= 0)
{
// Series expansion for small a.
eval_log(t, x);
eval_multiply(t, a);
hyp0F0(result, t);
return;
}
else
{
// Series expansion for moderately sized x. Note that for large power of a,
// the power of the integer part of a is calculated using the pown function.
if(an)
{
da.negate();
t = si_type(1);
eval_subtract(t, x);
hyp1F0(result, da, t);
detail::pow_imp(t, x, an, mpl::true_());
eval_multiply(result, t);
}
else
{
da = a;
da.negate();
t = si_type(1);
eval_subtract(t, x);
hyp1F0(result, da, t);
}
}
}
else
{
// Series expansion for pow(x, a). Note that for large power of a, the power
// of the integer part of a is calculated using the pown function.
if(an)
{
eval_log(t, x);
eval_multiply(t, da);
eval_exp(result, t);
detail::pow_imp(t, x, an, mpl::true_());
eval_multiply(result, t);
}
else
{
eval_log(t, x);
eval_multiply(t, a);
eval_exp(result, t);
}
}
}
