aboutsummaryrefslogtreecommitdiffhomepage
path: root/modules/skjson/include/SkJSON.h
diff options
context:
space:
mode:
Diffstat (limited to 'modules/skjson/include/SkJSON.h')
-rw-r--r--modules/skjson/include/SkJSON.h280
1 files changed, 250 insertions, 30 deletions
diff --git a/modules/skjson/include/SkJSON.h b/modules/skjson/include/SkJSON.h
index 4cb312c64f..99da29de72 100644
--- a/modules/skjson/include/SkJSON.h
+++ b/modules/skjson/include/SkJSON.h
@@ -9,8 +9,10 @@
#define SkJSON_DEFINED
#include "SkArenaAlloc.h"
+#include "SkTo.h"
#include "SkTypes.h"
+class SkString;
class SkWStream;
namespace skjson {
@@ -27,12 +29,26 @@ namespace skjson {
*
* Values are opaque, fixed-size (64 bits), immutable records.
*
- * They can be freely converted to any of the facade types for type-specific functionality.
+ * They can be converted to facade types for type-specific functionality.
*
- * Note: type checking is lazy/deferred, to facilitate chained property access - e.g.
+ * E.g.:
*
- * if (!v.as<ObjectValue>()["foo"].as<ObjectValue>()["bar"].is<NullValue>())
- * LOG("found v.foo.bar!");
+ * if (v.is<ArrayValue>()) {
+ * for (const auto& item : v.as<ArrayValue>()) {
+ * if (const NumberValue* n = item) {
+ * printf("Found number: %f", **n);
+ * }
+ * }
+ * }
+ *
+ * if (v.is<ObjectValue>()) {
+ * const StringValue* id = v.as<ObjectValue>()["id"];
+ * if (id) {
+ * printf("Found object ID: %s", id->begin());
+ * } else {
+ * printf("Missing object ID");
+ * }
+ * }
*/
class alignas(8) Value {
public:
@@ -46,7 +62,7 @@ public:
};
/**
- * @return The public type of this record.
+ * @return The type of this value.
*/
Type getType() const;
@@ -54,85 +70,289 @@ public:
* @return True if the record matches the facade type T.
*/
template <typename T>
- bool is() const { return T::IsType(this->getType()); }
+ bool is() const { return this->getType() == T::kType; }
/**
- * @return The record cast as facade type T.
+ * Unguarded conversion to facade types.
*
- * Note: this is always safe, as proper typing is enforced in the facade methods.
+ * @return The record cast as facade type T&.
*/
template <typename T>
const T& as() const {
- return *reinterpret_cast<const T*>(this->is<T>() ? this : &Value::Null());
+ SkASSERT(this->is<T>());
+ return *reinterpret_cast<const T*>(this);
}
/**
- * @return Null value singleton.
+ * Guarded conversion to facade types.
+ *
+ * @return The record cast as facade type T*.
*/
- static const Value& Null();
+ template <typename T>
+ operator const T*() const {
+ return this->is<T>() ? &this->as<T>() : nullptr;
+ }
+
+ /**
+ * @return The string representation of this value.
+ */
+ SkString toString() const;
protected:
- uint8_t fData8[8];
+ /*
+ Value implementation notes:
+
+ -- fixed 64-bit size
+
+ -- 8-byte aligned
+
+ -- union of:
+
+ bool
+ int32
+ float
+ char[8] (short string storage)
+ external payload (tagged) pointer
+
+ -- highest 3 bits reserved for type storage
+
+ */
+ enum class Tag : uint8_t {
+ // We picked kShortString == 0 so that tag 0x00 and stored max_size-size (7-7=0)
+ // conveniently overlap the '\0' terminator, allowing us to store a 7 character
+ // C string inline.
+ kShortString = 0b00000000, // inline payload
+ kNull = 0b00100000, // no payload
+ kBool = 0b01000000, // inline payload
+ kInt = 0b01100000, // inline payload
+ kFloat = 0b10000000, // inline payload
+ kString = 0b10100000, // ptr to external storage
+ kArray = 0b11000000, // ptr to external storage
+ kObject = 0b11100000, // ptr to external storage
+ };
+ static constexpr uint8_t kTagMask = 0b11100000;
+
+ void init_tagged(Tag);
+ void init_tagged_pointer(Tag, void*);
+
+ Tag getTag() const {
+ return static_cast<Tag>(fData8[kTagOffset] & kTagMask);
+ }
+
+ // Access the record data as T.
+ //
+ // This is also used to access the payload for inline records. Since the record type lives in
+ // the high bits, sizeof(T) must be less than sizeof(Value) when accessing inline payloads.
+ //
+ // E.g.
+ //
+ // uint8_t
+ // -----------------------------------------------------------------------
+ // | val8 | val8 | val8 | val8 | val8 | val8 | val8 | TYPE|
+ // -----------------------------------------------------------------------
+ //
+ // uint32_t
+ // -----------------------------------------------------------------------
+ // | val32 | unused | TYPE|
+ // -----------------------------------------------------------------------
+ //
+ // T* (64b)
+ // -----------------------------------------------------------------------
+ // | T* (kTypeShift bits) |TYPE|
+ // -----------------------------------------------------------------------
+ //
+ template <typename T>
+ const T* cast() const {
+ static_assert(sizeof (T) <= sizeof(Value), "");
+ static_assert(alignof(T) <= alignof(Value), "");
+ return reinterpret_cast<const T*>(this);
+ }
+
+ template <typename T>
+ T* cast() { return const_cast<T*>(const_cast<const Value*>(this)->cast<T>()); }
+
+ // Access the pointer payload.
+ template <typename T>
+ const T* ptr() const {
+ static_assert(sizeof(uintptr_t) == sizeof(Value) ||
+ sizeof(uintptr_t) * 2 == sizeof(Value), "");
+
+ return (sizeof(uintptr_t) < sizeof(Value))
+ // For 32-bit, pointers are stored unmodified.
+ ? *this->cast<const T*>()
+ // For 64-bit, we use the high bits of the pointer as tag storage.
+ : reinterpret_cast<T*>(*this->cast<uintptr_t>() & kTagPointerMask);
+ }
+
+private:
+ static constexpr size_t kValueSize = 8;
+
+ uint8_t fData8[kValueSize];
+
+#if defined(SK_CPU_LENDIAN)
+ static constexpr size_t kTagOffset = kValueSize - 1;
+
+ static constexpr uintptr_t kTagPointerMask =
+ ~(static_cast<uintptr_t>(kTagMask) << ((sizeof(uintptr_t) - 1) * 8));
+#else
+ // The current value layout assumes LE and will take some tweaking for BE.
+ static_assert(false, "Big-endian builds are not supported at this time.");
+#endif
};
class NullValue final : public Value {
public:
- static bool IsType(Value::Type t) { return t == Type::kNull; }
+ static constexpr Type kType = Type::kNull;
+
+ NullValue();
};
-template <typename T, Value::Type vtype>
-class PrimitiveValue final : public Value {
+class BoolValue final : public Value {
public:
- static bool IsType(Value::Type t) { return t == vtype; }
+ static constexpr Type kType = Type::kBool;
+
+ explicit BoolValue(bool);
- T operator *() const;
+ bool operator *() const {
+ SkASSERT(this->getTag() == Tag::kBool);
+ return *this->cast<bool>();
+ }
+};
+
+class NumberValue final : public Value {
+public:
+ static constexpr Type kType = Type::kNumber;
+
+ explicit NumberValue(int32_t);
+ explicit NumberValue(float);
+
+ double operator *() const {
+ SkASSERT(this->getTag() == Tag::kInt ||
+ this->getTag() == Tag::kFloat);
+
+ return this->getTag() == Tag::kInt
+ ? static_cast<double>(*this->cast<int32_t>())
+ : static_cast<double>(*this->cast<float>());
+ }
};
template <typename T, Value::Type vtype>
class VectorValue : public Value {
public:
- static bool IsType(Value::Type t) { return t == vtype; }
+ using ValueT = T;
+ static constexpr Type kType = vtype;
- size_t size() const;
+ size_t size() const {
+ SkASSERT(this->getType() == kType);
+ return *this->ptr<size_t>();
+ }
- const T* begin() const;
- const T* end() const;
+ const T* begin() const {
+ SkASSERT(this->getType() == kType);
+ const auto* size_ptr = this->ptr<size_t>();
+ return reinterpret_cast<const T*>(size_ptr + 1);
+ }
+
+ const T* end() const {
+ SkASSERT(this->getType() == kType);
+ const auto* size_ptr = this->ptr<size_t>();
+ return reinterpret_cast<const T*>(size_ptr + 1) + *size_ptr;
+ }
const T& operator[](size_t i) const {
- return (i < this->size()) ? *(this->begin() + i) : T::Null();
+ SkASSERT(this->getType() == kType);
+ SkASSERT(i < this->size());
+
+ return *(this->begin() + i);
}
};
-using BoolValue = PrimitiveValue<bool , Value::Type::kBool >;
-using NumberValue = PrimitiveValue<double, Value::Type::kNumber>;
-using StringValue = VectorValue<char , Value::Type::kString>;
-using ArrayValue = VectorValue<Value , Value::Type::kArray >;
+class ArrayValue final : public VectorValue<Value, Value::Type::kArray> {
+public:
+ ArrayValue(const Value* src, size_t size, SkArenaAlloc& alloc);
+};
+
+class StringValue final : public Value {
+public:
+ static constexpr Type kType = Type::kString;
+
+ StringValue();
+ StringValue(const char* src, size_t size, SkArenaAlloc& alloc);
+
+ size_t size() const {
+ switch (this->getTag()) {
+ case Tag::kShortString:
+ return kMaxInlineStringSize - SkToSizeT(this->cast<char>()[kMaxInlineStringSize]);
+ case Tag::kString:
+ return this->cast<VectorValue<char, Value::Type::kString>>()->size();
+ default:
+ return 0;
+ }
+ }
+
+ const char* begin() const {
+ return this->getTag() == Tag::kShortString
+ ? this->cast<char>()
+ : this->cast<VectorValue<char, Value::Type::kString>>()->begin();
+ }
+
+ const char* end() const {
+ if (this->getTag() == Tag::kShortString) {
+ const auto* payload = this->cast<char>();
+ return payload + kMaxInlineStringSize - SkToSizeT(payload[kMaxInlineStringSize]);
+ }
+ return this->cast<VectorValue<char, Value::Type::kString>>()->end();
+ }
+
+private:
+ static constexpr size_t kMaxInlineStringSize = sizeof(Value) - 1;
+};
struct Member {
StringValue fKey;
Value fValue;
-
- static const Member& Null();
};
class ObjectValue final : public VectorValue<Member, Value::Type::kObject> {
public:
+ ObjectValue(const Member* src, size_t size, SkArenaAlloc& alloc);
+
const Value& operator[](const char*) const;
+
+private:
+ // Not particularly interesting - hiding for disambiguation.
+ const Member& operator[](size_t i) const = delete;
};
class DOM final : public SkNoncopyable {
public:
explicit DOM(const char*);
- const Value& root() const { return *fRoot; }
+ const Value& root() const { return fRoot; }
void write(SkWStream*) const;
private:
SkArenaAlloc fAlloc;
- const Value* fRoot;
+ Value fRoot;
};
+inline Value::Type Value::getType() const {
+ switch (this->getTag()) {
+ case Tag::kNull: return Type::kNull;
+ case Tag::kBool: return Type::kBool;
+ case Tag::kInt: return Type::kNumber;
+ case Tag::kFloat: return Type::kNumber;
+ case Tag::kShortString: return Type::kString;
+ case Tag::kString: return Type::kString;
+ case Tag::kArray: return Type::kArray;
+ case Tag::kObject: return Type::kObject;
+ }
+
+ SkASSERT(false); // unreachable
+ return Type::kNull;
+}
+
} // namespace skjson
#endif // SkJSON_DEFINED
generated by cgit v1.2.3 (git 2.39.1) at 2024-05-10 05:37:53 +0000