diff options
author | Mike Klein <mtklein@google.com> | 2018-06-13 18:57:02 +0000 |
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committer | Skia Commit-Bot <skia-commit-bot@chromium.org> | 2018-06-13 18:57:06 +0000 |
commit | e4b900bfd92f7f2c387b13713f850af5547a5a46 (patch) | |
tree | 9c89a7b821b9f0bc17576dd74512db9233b0f8ba /include/private/SkTFitsIn.h | |
parent | a2bf58515ae2d55882668287c8d0ee77e01f0fe8 (diff) |
Revert "simplify SkTFitsIn, try 2"
This reverts commit 009f51e43fee199a579ecdd773e3aa35aaa3b8b8.
Reason for revert: unintentional header consequences in Chromium... will reland after fixing Chromium
Original change's description:
> simplify SkTFitsIn, try 2
>
> Originally we wrote this in C++14 constexpr,
> but because this is used from public headers, we can't use
> C++14 yet. Now a somewhat sillier looking C++11 version.
>
> All the old tests still pass, and one new added.
> Updated the comments a bit for correctness and readability.
>
> Change-Id: I99c01e1346c1a5a36278cc08f30538112e5259aa
> Reviewed-on: https://skia-review.googlesource.com/134425
> Commit-Queue: Mike Klein <mtklein@chromium.org>
> Commit-Queue: Ben Wagner <bungeman@google.com>
> Auto-Submit: Mike Klein <mtklein@chromium.org>
> Reviewed-by: Ben Wagner <bungeman@google.com>
TBR=mtklein@chromium.org,bungeman@google.com
Change-Id: Ic73f8800bd022ffea125b3b1bf138fe49c0db926
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/134621
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Diffstat (limited to 'include/private/SkTFitsIn.h')
-rw-r--r-- | include/private/SkTFitsIn.h | 195 |
1 files changed, 166 insertions, 29 deletions
diff --git a/include/private/SkTFitsIn.h b/include/private/SkTFitsIn.h index 9dcfdf3384..09fa3449aa 100644 --- a/include/private/SkTFitsIn.h +++ b/include/private/SkTFitsIn.h @@ -8,7 +8,7 @@ #ifndef SkTFitsIn_DEFINED #define SkTFitsIn_DEFINED -#include <cassert> +#include "../private/SkTLogic.h" #include <limits> #include <type_traits> @@ -25,20 +25,15 @@ * (uint16_t)(int8_t)0xFFFF == 0xFFFF => (uint16_t)-1 == 0xFFFF => 0xFFFF == 0xFFFF => true. * * Consider the cases: - * u = unsigned, less digits - * U = unsigned, more digits - * s = signed, less digits - * S = signed, more digits - * v is the value we're considering. - * - * u -> U: (u)(U)v == v, trivially true - * U -> u: (U)(u)v == v, both casts well defined, test works - * s -> S: (s)(S)v == v, trivially true - * S -> s: (S)(s)v == v, first cast implementation value, second cast defined, test works - * s -> U: (s)(U)v == v, *this is bad*, the second cast results in implementation defined value - * S -> u: (S)(u)v == v, the second cast is required to prevent promotion of rhs to unsigned - * u -> S: (u)(S)v == v, trivially true - * U -> s: (U)(s)v == v, *this is bad*, + * u = unsigned, s = signed, X = more digits, x = less digits + * ux -> uX: (ux)(uX)ux == ux, trivially true + * uX -> ux: (uX)(ux)uX == uX, both casts well defined, test works + * sx -> sX: (sx)(sX)sx == sx, trivially true + * sX -> sx: (sX)(sx)sX == sX, first cast implementation value, second cast defined, test works + * sx -> uX: (sx)(uX)sx == sx, this is bad, the second cast results in implementation defined value + * sX -> ux: (sX)(ux)sX == sX, the second cast is required to prevent promotion of rhs to unsigned + * ux -> sX: (ux)(sX)ux == ux, trivially true + * uX -> sx: (uX)(sx)uX == uX, this is bad, * first cast results in implementation defined value, * second cast is defined. However, this creates false positives * uint16_t x = 0xFFFF @@ -49,25 +44,167 @@ * * So for the eight cases three are trivially true, three more are valid casts, and two are special. * The two 'full' checks which otherwise require two comparisons are valid cast checks. - * The two remaining checks s -> U [v >= 0] and U -> s [v <= max(s)] can be done with one op. + * The two remaining checks uX -> sx [uX < max(sx)] and sx -> uX [sx > 0] can be done with one op. */ -template <typename D, typename S> -static constexpr inline bool SkTFitsIn(S src) { - // SkTFitsIn() is used in public headers, so needs to be written targeting at most C++11. - return assert(std::is_integral<S>::value || std::is_enum<S>::value), - assert(std::is_integral<D>::value || std::is_enum<D>::value), +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> +{ }; + +/** Returns true. + * Used when it is statically known that source values are in the range of the Destination. + */ +template <typename S> struct SkTInRange_True { + static constexpr bool fits(S) { + return true; + } +}; + +/** Tests that (S)(D)s == s. + * This is not valid for uX -> sx and sx -> uX conversions. + */ +template <typename D, typename S> struct SkTInRange_Cast { + static constexpr bool fits(S s) { + using S_is_bigger = SkTHasMoreDigits<S, D>; + using D_is_bigger = SkTHasMoreDigits<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 precondition = skstd::bool_constant< + !((!S_is_signed::value && D_is_signed::value && S_is_bigger::value) || + ( S_is_signed::value && !D_is_signed::value && D_is_bigger::value) )>; + static_assert(precondition::value, "not valid for uX -> sx and sx -> uX conversions"); + + return static_cast<S>(static_cast<D>(s)) == s; + } +}; + +/** Tests if the source value <= Max(D). + * Assumes that Max(S) >= Max(D). + */ +template <typename D, typename S> struct SkTInRange_LE_MaxD { + static constexpr bool fits(S s) { + using precondition = SkTHasMoreDigits<S, D>; + static_assert(precondition::value, "maxS < maxD"); + + return s <= static_cast<S>((std::numeric_limits<D>::max)()); + + } +}; + +/** Tests if the source value >= 0. */ +template <typename D, typename S> struct SkTInRange_GE_Zero { + static constexpr bool fits(S s) { + return static_cast<S>(0) <= s; + } +}; + +/** SkTFitsIn_Unsigned2Unsiged::type is an SkTInRange with an fits(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 CastCheck = SkTInRange_Cast<D, S>; + using NoCheck = SkTInRange_True<S>; + + // If std::numeric_limits<D>::digits >= std::numeric_limits<S>::digits, nothing to check. + using sourceFitsInDesitination = SkTHasMoreDigits<D, S>; + using type = skstd::conditional_t<sourceFitsInDesitination::value, NoCheck, CastCheck>; +}; + +/** SkTFitsIn_Signed2Signed::type is an SkTInRange with an fits(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 CastCheck = SkTInRange_Cast<D, S>; + using NoCheck = SkTInRange_True<S>; + + // If std::numeric_limits<D>::digits >= std::numeric_limits<S>::digits, nothing to check. + using sourceFitsInDesitination = SkTHasMoreDigits<D, S>; + using type = skstd::conditional_t<sourceFitsInDesitination::value, NoCheck, CastCheck>; +}; + +/** SkTFitsIn_Signed2Unsigned::type is an SkTInRange with an fits(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 CastCheck = SkTInRange_Cast<D, S>; + using LowSideOnlyCheck = SkTInRange_GE_Zero<D, 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 SkTInRange_Cast. + using sourceCannotExceedDest = SkTHasMoreDigits<D, S>; + using type = skstd::conditional_t<sourceCannotExceedDest::value, LowSideOnlyCheck, CastCheck>; +}; + +/** SkTFitsIn_Unsigned2Signed::type is an SkTInRange with an fits(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 HighSideCheck = SkTInRange_LE_MaxD<D, S>; + using NoCheck = SkTInRange_True<S>; + + // If std::numeric_limits<D>::max() >= std::numeric_limits<S>::max(), nothing to check. + // (Until C++11, assume more digits means greater max.) + using sourceCannotExceedDest = SkTHasMoreDigits<D, S>; + using type = skstd::conditional_t<sourceCannotExceedDest::value, NoCheck, HighSideCheck>; +}; + +/** SkTFitsIn::type is an SkTInRange with an fits(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 SkTInRange. + 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 - // E.g. (int8_t)(uint8_t) int8_t(-1) == -1, but the uint8_t == 255, not -1. - (std::is_signed<S>::value && std::is_unsigned<D>::value && sizeof(S) <= sizeof(D)) ? - (S)0 <= src : +/** Returns true if the integer source value 's' will fit in the integer destination type 'D'. */ +template <typename D, typename S> constexpr 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."); - // E.g. (uint8_t)(int8_t) uint8_t(255) == 255, but the int8_t == -1. - (std::is_signed<D>::value && std::is_unsigned<S>::value && sizeof(D) <= sizeof(S)) ? - src <= (S)std::numeric_limits<D>::max() : + using RealS = typename sktfitsin::Private::underlying_type<S>::type; + using RealD = typename sktfitsin::Private::underlying_type<D>::type; - // else - (S)(D)src == src; + return sktfitsin::Private::SkTFitsIn<RealD, RealS>::type::fits(static_cast<RealS>(s)); } #endif |