include/o3tl/float_int_conversion.hxx

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   2 /*
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   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
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   9
  10 #ifndef INCLUDED_O3TL_FLOAT_INT_CONVERSION_HXX
  11 #define INCLUDED_O3TL_FLOAT_INT_CONVERSION_HXX
  12
  13 #include <sal/config.h>
  14
  15 #include <cmath>
  16 #include <limits>
  17 #include <type_traits>
  18
  19 namespace o3tl
  20 {
  21 // Return true iff `value` of floating-point type `F` converts to a value of integral type `I` no
  22 // smaller than `min`:
  23 template <typename F, typename I>
  24 constexpr std::enable_if_t<std::is_floating_point_v<F> && std::is_integral_v<I>, bool>
  25 convertsToAtLeast(F value, I min)
  26 {
  27     // If `F(min)`, `F(min) - F(1)` are too large in magnitude for `F`'s precision, then they either
  28     // fall into the same bucket, in which case we should return false if `value` represents that
  29     // bucket, or they are on the boundary of two adjacent buckets, in which case we should return
  30     // true if `value`represents the higher bucket containing `F(min)`:
  31     return value > F(min) - F(1);
  32 }
  33
  34 // Return true iff `value` of floating-point type `F` converts to a value of integral type `I` no
  35 // larger than `max`:
  36 template <typename F, typename I>
  37 constexpr std::enable_if_t<std::is_floating_point_v<F> && std::is_integral_v<I>, bool>
  38 convertsToAtMost(F value, I max)
  39 {
  40     // If `F(max)`, `F(max) + F(1)` are too large in magnitude for `F`'s precision, then they either
  41     // fall into the same bucket, in which case we should return false if `value` represents that
  42     // bucket, or they are on the boundary of two adjacent buckets, in which case we should return
  43     // true if `value`represents the lower bucket containing `F(max)`:
  44     return value < F(max) + F(1);
  45 }
  46
  47 // Casts a floating-point to an integer, avoiding overflow. Used like:
  48 //     sal_Int64 n = o3tl::saturating_cast<sal_Int64>(f);
  49 template <typename I, typename F>
  50 constexpr std::enable_if_t<std::is_floating_point_v<F> && std::is_integral_v<I>, I>
  51 saturating_cast(F f)
  52 {
  53     if constexpr (std::is_signed_v<I>)
  54         if (!convertsToAtLeast(f, std::numeric_limits<I>::min()))
  55             return std::numeric_limits<I>::min();
  56     if (!convertsToAtMost(f, std::numeric_limits<I>::max()))
  57         return std::numeric_limits<I>::max();
  58     return f;
  59 }
  60
  61 // Return `value` of floating-point type `F` rounded to the nearest integer away from zero (which
  62 // can be useful in calls to convertsToAtLeast/Most(roundAway(x), n), to reject x that are
  63 // smaller/larger than n because they have a fractional part):
  64 template <typename F> std::enable_if_t<std::is_floating_point_v<F>, F> roundAway(F value)
  65 {
  66     return value >= 0 ? std::ceil(value) : std::floor(value);
  67 }
  68 }
  69
  70 #endif
  71
  72 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */