skia2/include/private/SkTFitsIn.h

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/*
* Copyright 2013 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkTFitsIn_DEFINED
#define SkTFitsIn_DEFINED
#include "../private/SkTLogic.h"
#include <limits>
#include <type_traits>
namespace sktfitsin {
namespace Private {
/** SkTMux::type = (a && b) ? Both : (a) ? A : (b) ? B : Neither; */
template <bool a, bool b, typename Both, typename A, typename B, typename Neither>
struct SkTMux {
using type = skstd::conditional_t<a, skstd::conditional_t<b, Both, A>,
skstd::conditional_t<b, B, Neither>>;
};
/** SkTHasMoreDigits = (digits(A) >= digits(B)) ? true_type : false_type. */
template <typename A, typename B> struct SkTHasMoreDigits
: skstd::bool_constant<std::numeric_limits<A>::digits >= std::numeric_limits<B>::digits>
{ };
/** A high or low side predicate which is used when it is statically known
* that source values are in the range of the Destination.
*/
template <typename S> struct SkTOutOfRange_False {
using can_be_true = std::false_type;
using source_type = S;
static bool apply(S) {
return false;
}
};
/** A low side predicate which tests if the source value < Min(D).
* Assumes that Min(S) <= Min(D).
*/
template <typename D, typename S> struct SkTOutOfRange_LT_MinD {
using can_be_true = std::true_type;
using source_type = S;
static bool apply(S s) {
using precondition = SkTHasMoreDigits<S, D>;
static_assert(precondition::value, "minS > minD");
return s < static_cast<S>((std::numeric_limits<D>::min)());
}
};
/** A low side predicate which tests if the source value is less than 0. */
template <typename D, typename S> struct SkTOutOfRange_LT_Zero {
using can_be_true = std::true_type;
using source_type = S;
static bool apply(S s) {
return s < static_cast<S>(0);
}
};
/** A high side predicate which tests if the source value > Max(D).
* Assumes that Max(S) >= Max(D).
*/
template <typename D, typename S> struct SkTOutOfRange_GT_MaxD {
using can_be_true = std::true_type;
using source_type = S;
static bool apply(S s) {
using precondition = SkTHasMoreDigits<S, D>;
static_assert(precondition::value, "maxS < maxD");
return s > static_cast<S>((std::numeric_limits<D>::max)());
}
};
/** Composes two SkTOutOfRange predicates.
* First checks OutOfRange_Low then, if in range, OutOfRange_High.
*/
template <typename OutOfRange_Low, typename OutOfRange_High> struct SkTOutOfRange_Either {
using can_be_true = std::true_type;
using source_type = typename OutOfRange_Low::source_type;
static bool apply(source_type s) {
bool outOfRange = OutOfRange_Low::apply(s);
if (!outOfRange) {
outOfRange = OutOfRange_High::apply(s);
}
return outOfRange;
}
};
/** SkTCombineOutOfRange::type is an SkTOutOfRange_XXX type which is the
* optimal combination of OutOfRange_Low and OutOfRange_High.
*/
template <typename OutOfRange_Low, typename OutOfRange_High> struct SkTCombineOutOfRange {
using Both = SkTOutOfRange_Either<OutOfRange_Low, OutOfRange_High>;
using Neither = SkTOutOfRange_False<typename OutOfRange_Low::source_type>;
using apply_low = typename OutOfRange_Low::can_be_true;
using apply_high = typename OutOfRange_High::can_be_true;
using type = typename SkTMux<apply_low::value, apply_high::value,
Both, OutOfRange_Low, OutOfRange_High, Neither>::type;
};
template <typename D, typename S, typename OutOfRange_Low, typename OutOfRange_High>
struct SkTRangeChecker {
/** This is the method which is called at runtime to do the range check. */
static bool OutOfRange(S s) {
using Combined = typename SkTCombineOutOfRange<OutOfRange_Low, OutOfRange_High>::type;
return Combined::apply(s);
}
};
/** SkTFitsIn_Unsigned2Unsiged::type is an SkTRangeChecker with an OutOfRange(S s) method
* the implementation of which is tailored for the source and destination types.
* Assumes that S and D are unsigned integer types.
*/
template <typename D, typename S> struct SkTFitsIn_Unsigned2Unsiged {
using OutOfRange_Low = SkTOutOfRange_False<S>;
using OutOfRange_High = SkTOutOfRange_GT_MaxD<D, S>;
using HighSideOnlyCheck = SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High>;
using NoCheck = SkTRangeChecker<D, S, SkTOutOfRange_False<S>, SkTOutOfRange_False<S>>;
// If std::numeric_limits<D>::digits >= std::numeric_limits<S>::digits, nothing to check.
// This also protects the precondition of SkTOutOfRange_GT_MaxD.
using sourceFitsInDesitination = SkTHasMoreDigits<D, S>;
using type = skstd::conditional_t<sourceFitsInDesitination::value, NoCheck, HighSideOnlyCheck>;
};
/** SkTFitsIn_Signed2Signed::type is an SkTRangeChecker with an OutOfRange(S s) method
* the implementation of which is tailored for the source and destination types.
* Assumes that S and D are signed integer types.
*/
template <typename D, typename S> struct SkTFitsIn_Signed2Signed {
using OutOfRange_Low = SkTOutOfRange_LT_MinD<D, S>;
using OutOfRange_High = SkTOutOfRange_GT_MaxD<D, S>;
using FullCheck = SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High>;
using NoCheck = SkTRangeChecker<D, S, SkTOutOfRange_False<S>, SkTOutOfRange_False<S>>;
// If std::numeric_limits<D>::digits >= std::numeric_limits<S>::digits, nothing to check.
// This also protects the precondition of SkTOutOfRange_LT_MinD and SkTOutOfRange_GT_MaxD.
using sourceFitsInDesitination = SkTHasMoreDigits<D, S>;
using type = skstd::conditional_t<sourceFitsInDesitination::value, NoCheck, FullCheck>;
};
/** SkTFitsIn_Signed2Unsigned::type is an SkTRangeChecker with an OutOfRange(S s) method
* the implementation of which is tailored for the source and destination types.
* Assumes that S is a signed integer type and D is an unsigned integer type.
*/
template <typename D, typename S> struct SkTFitsIn_Signed2Unsigned {
using OutOfRange_Low = SkTOutOfRange_LT_Zero<D, S>;
using OutOfRange_High = SkTOutOfRange_GT_MaxD<D, S>;
using FullCheck = SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High>;
using LowSideOnlyCheck = SkTRangeChecker<D, S, OutOfRange_Low, SkTOutOfRange_False<S>>;
// If std::numeric_limits<D>::max() >= std::numeric_limits<S>::max(),
// no need to check the high side. (Until C++11, assume more digits means greater max.)
// This also protects the precondition of SkTOutOfRange_GT_MaxD.
using sourceCannotExceedDest = SkTHasMoreDigits<D, S>;
using type = skstd::conditional_t<sourceCannotExceedDest::value, LowSideOnlyCheck, FullCheck>;
};
/** SkTFitsIn_Unsigned2Signed::type is an SkTRangeChecker with an OutOfRange(S s) method
* the implementation of which is tailored for the source and destination types.
* Assumes that S is an usigned integer type and D is a signed integer type.
*/
template <typename D, typename S> struct SkTFitsIn_Unsigned2Signed {
using OutOfRange_Low = SkTOutOfRange_False<S>;
using OutOfRange_High = SkTOutOfRange_GT_MaxD<D, S>;
using HighSideOnlyCheck = SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High>;
using NoCheck = SkTRangeChecker<D, S, SkTOutOfRange_False<S>, SkTOutOfRange_False<S>>;
// If std::numeric_limits<D>::max() >= std::numeric_limits<S>::max(), nothing to check.
// (Until C++11, assume more digits means greater max.)
// This also protects the precondition of SkTOutOfRange_GT_MaxD.
using sourceCannotExceedDest = SkTHasMoreDigits<D, S>;
using type = skstd::conditional_t<sourceCannotExceedDest::value, NoCheck, HighSideOnlyCheck>;
};
/** SkTFitsIn::type is an SkTRangeChecker with an OutOfRange(S s) method
* the implementation of which is tailored for the source and destination types.
* Assumes that S and D are integer types.
*/
template <typename D, typename S> struct SkTFitsIn {
// One of the following will be the 'selector' type.
using S2S = SkTFitsIn_Signed2Signed<D, S>;
using S2U = SkTFitsIn_Signed2Unsigned<D, S>;
using U2S = SkTFitsIn_Unsigned2Signed<D, S>;
using U2U = SkTFitsIn_Unsigned2Unsiged<D, S>;
using S_is_signed = skstd::bool_constant<std::numeric_limits<S>::is_signed>;
using D_is_signed = skstd::bool_constant<std::numeric_limits<D>::is_signed>;
using selector = typename SkTMux<S_is_signed::value, D_is_signed::value,
S2S, S2U, U2S, U2U>::type;
// This type is an SkTRangeChecker.
using type = typename selector::type;
};
template <typename T, bool = std::is_enum<T>::value> struct underlying_type {
using type = skstd::underlying_type_t<T>;
};
template <typename T> struct underlying_type<T, false> {
using type = T;
};
} // namespace Private
} // namespace sktfitsin
/** Returns true if the integer source value 's' will fit in the integer destination type 'D'. */
template <typename D, typename S> inline bool SkTFitsIn(S s) {
static_assert(std::is_integral<S>::value || std::is_enum<S>::value, "S must be integral.");
static_assert(std::is_integral<D>::value || std::is_enum<D>::value, "D must be integral.");
using RealS = typename sktfitsin::Private::underlying_type<S>::type;
using RealD = typename sktfitsin::Private::underlying_type<D>::type;
return !sktfitsin::Private::SkTFitsIn<RealD, RealS>::type::OutOfRange(s);
}
#endif