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authorGravatar Mike Klein <mtklein@chromium.org>2018-06-11 11:56:57 -0400
committerGravatar Skia Commit-Bot <skia-commit-bot@chromium.org>2018-06-12 15:44:23 +0000
commitb82c3d6ff2ac62c8a14b38b0d658a51e7d8cf81e (patch)
tree5d6c9bbf90bd0c98b05bcfcfd33bc460bc12e5ab /include
parente5b7e6d2ea4f0d0dc8838bd265ea29b00ce3cc3e (diff)
simplify SkTFitsIn
Now that we're C++14, a constexpr SkTFitsIn() is a lot easier. All the old tests still pass, and one new added. Updated the comments a bit for correctness and readability. Change-Id: I0f60e32e545fe4f2fb14e66a2bf25d562dbd680f Reviewed-on: https://skia-review.googlesource.com/133831 Reviewed-by: Ben Wagner <bungeman@google.com> Commit-Queue: Mike Klein <mtklein@chromium.org>
Diffstat (limited to 'include')
-rw-r--r--include/private/SkTFitsIn.h190
1 files changed, 26 insertions, 164 deletions
diff --git a/include/private/SkTFitsIn.h b/include/private/SkTFitsIn.h
index 09fa3449aa..65557f110f 100644
--- a/include/private/SkTFitsIn.h
+++ b/include/private/SkTFitsIn.h
@@ -8,7 +8,6 @@
#ifndef SkTFitsIn_DEFINED
#define SkTFitsIn_DEFINED
-#include "../private/SkTLogic.h"
#include <limits>
#include <type_traits>
@@ -25,15 +24,20 @@
* (uint16_t)(int8_t)0xFFFF == 0xFFFF => (uint16_t)-1 == 0xFFFF => 0xFFFF == 0xFFFF => true.
*
* Consider the cases:
- * 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,
+ * 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*,
* first cast results in implementation defined value,
* second cast is defined. However, this creates false positives
* uint16_t x = 0xFFFF
@@ -44,167 +48,25 @@
*
* 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 uX -> sx [uX < max(sx)] and sx -> uX [sx > 0] can be done with one op.
- */
-
-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.
+ * The two remaining checks s -> U [v >= 0] and U -> s [v <= max(s)] can be done with one op.
*/
-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>;
+template <typename D, typename S>
+constexpr inline bool SkTFitsIn(S src) {
+ static_assert(std::is_integral<S>::value || std::is_enum<S>::value, "");
+ static_assert(std::is_integral<D>::value || std::is_enum<D>::value, "");
- 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;
+ // E.g. (int8_t)(uint8_t) int8_t(-1) == -1, but the uint8_t == 255, not -1.
+ if (std::is_signed<S>::value && std::is_unsigned<D>::value && sizeof(S) <= sizeof(D)) {
+ return (S)0 <= src;
}
-};
-
-/** 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)());
+ // E.g. (uint8_t)(int8_t) uint8_t(255) == 255, but the int8_t == -1.
+ if (std::is_signed<D>::value && std::is_unsigned<S>::value && sizeof(D) <= sizeof(S)) {
+ return src <= (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
-
-/** 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.");
-
- 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::fits(static_cast<RealS>(s));
+ return (S)(D)src == src;
}
#endif