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AP_Math: use right epsilon for is_equal()

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We are calling fabsf(), which returns a float. We should use the epsilon
from float type, not from the argument type passed to fabsf().

On the other hand when the double version is instantiated we do want to
use the std::numeric_limits<double>::epsilon() value.

This adds a branch to the function, but it's removed when the function
is intantiated by the compiler since the type is known at compile-time.

Fixes this warning when building for PX4:
../../libraries/AP_Math/AP_Math.cpp: In instantiation of 'typename std::enable_if<std::is_floating_point<typename std::common_type<_Tp, _Up>::type>::value, bool>::type is_equal(Arithmetic1, Arithmetic2) [with Arithmetic1 = double; Arithmetic2 = double; typename std::enable_if<std::is_floating_point<typename std::common_type<_Tp, _Up>::type>::value, bool>::type = bool]':
../../libraries/AP_Math/AP_Math.cpp:23:66:   required from here
../../libraries/AP_Math/AP_Math.cpp:17:29: warning: implicit conversion from 'float' to 'double' to match other operand of binary expression [-Wdouble-promotion]
     return fabsf(v_1 - v_2) < std::numeric_limits<decltype(v_1 - v_2)>::epsilon();
                             ^
This commit is contained in:
Lucas De Marchi 2017-01-24 09:57:43 -08:00
parent 784fa6fed8
commit 4f8d2059f8
1 changed files with 16 additions and 1 deletions
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17
libraries/AP_Math/AP_Math.cpp
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@ -1,6 +1,12 @@
#include "AP_Math.h"
#include <float.h>
/*
* is_equal(): Integer implementation, provided for convenience and
* compatibility with old code. Expands to the same as comparing the values
* directly
*/
template <class Arithmetic1, class Arithmetic2>
typename std::enable_if<std::is_integral<typename std::common_type<Arithmetic1, Arithmetic2>::type>::value ,bool>::type
is_equal(const Arithmetic1 v_1, const Arithmetic2 v_2)
@ -9,11 +15,20 @@ is_equal(const Arithmetic1 v_1, const Arithmetic2 v_2)
return static_cast<common_type>(v_1) == static_cast<common_type>(v_2);
}
/*
* is_equal(): double/float implementation - takes into account
* std::numeric_limits<T>::epsilon() to return if 2 values are equal.
*/
template <class Arithmetic1, class Arithmetic2>
typename std::enable_if<std::is_floating_point<typename std::common_type<Arithmetic1, Arithmetic2>::type>::value, bool>::type
is_equal(const Arithmetic1 v_1, const Arithmetic2 v_2)
{
return fabsf(v_1 - v_2) < std::numeric_limits<decltype(v_1 - v_2)>::epsilon();
typedef typename std::common_type<Arithmetic1, Arithmetic2>::type common_type;
typedef typename std::remove_cv<common_type>::type common_type_nonconst;
if (std::is_same<double, common_type_nonconst>::value) {
return fabs(v_1 - v_2) < std::numeric_limits<double>::epsilon();
}
return fabsf(v_1 - v_2) < std::numeric_limits<float>::epsilon();
}
template bool is_equal<int>(const int v_1, const int v_2);