Add methods for creating and interacting with BigInt

Summary:
This change adds the following methods to jsi::BigInt

  * [static] fromInt64(value): creates a jsi::BigInt from a signed 64-bit value
  * [static] fromUint64(value): creates a jsi::BigInt from an unsigned 64-bit value
  * [static] strictEquals(a, b): return a === b, a and b are BigInts
  * asInt64(): truncates the BigInt to a single signed 64-bit integer; throws a JSIException if the truncation is lossy.
  * getInt64(): truncates the BigInt to a single signed 64-bit integer
  * isInt64(): returns true if the BigInt can be truncated losslessly to an int64_t
  * asUint64(): truncates the BigInt to a single unsigned 64-bit integer; throws a JSIException if the truncation is lossy.
  * getUint64(): truncates the BigInt to a single unsigned 64-bit integer
  * isUint64(): returns true if the BigInt can be truncated losslessly to an uint64_t
  * toString(radix): converts the BigInt to a string representing the number in the given radix.

 A lossy truncation is one that yields a result from which the BigInt cannot be reconstructed from, i.e.,
* BigInt::fromInt64(b.toInt64()) !== b
* BigInt::fromUint64(b.toUint64()) !== b

Changelog: [Internal]

Reviewed By: kodafb

Differential Revision: D37909139

fbshipit-source-id: 172848024f8367aed73cc602f38cde22f03cac8f

ReactCommon/jsi/JSCRuntime.cpp

@@ -158,6 +158,13 @@ class JSCRuntime : public jsi::Runtime {
 
   std::string symbolToString(const jsi::Symbol &) override;
 
+  jsi::BigInt createBigIntFromInt64(int64_t) override;
+  jsi::BigInt createBigIntFromUint64(uint64_t) override;
+  bool bigintIsInt64(const jsi::BigInt &) override;
+  bool bigintIsUint64(const jsi::BigInt &) override;
+  uint64_t truncate(const jsi::BigInt &) override;
+  jsi::String bigintToString(const jsi::BigInt &, int) override;
+
   jsi::String createStringFromAscii(const char *str, size_t length) override;
   jsi::String createStringFromUtf8(const uint8_t *utf8, size_t length) override;
   std::string utf8(const jsi::String &) override;
@@ -686,6 +693,30 @@ std::string JSCRuntime::symbolToString(const jsi::Symbol &sym) {
   return jsi::Value(*this, sym).toString(*this).utf8(*this);
 }
 
+jsi::BigInt JSCRuntime::createBigIntFromInt64(int64_t) {
+  throw std::logic_error("Not implemented");
+}
+
+jsi::BigInt JSCRuntime::createBigIntFromUint64(uint64_t) {
+  throw std::logic_error("Not implemented");
+}
+
+bool JSCRuntime::bigintIsInt64(const jsi::BigInt &) {
+  throw std::logic_error("Not implemented");
+}
+
+bool JSCRuntime::bigintIsUint64(const jsi::BigInt &) {
+  throw std::logic_error("Not implemented");
+}
+
+uint64_t JSCRuntime::truncate(const jsi::BigInt &) {
+  throw std::logic_error("Not implemented");
+}
+
+jsi::String JSCRuntime::bigintToString(const jsi::BigInt &, int) {
+  throw std::logic_error("Not implemented");
+}
+
 jsi::String JSCRuntime::createStringFromAscii(const char *str, size_t length) {
   // Yes we end up double casting for semantic reasons (UTF8 contains ASCII,
   // not the other way around)

ReactCommon/jsi/jsi/decorator.h

@@ -193,6 +193,25 @@ class RuntimeDecorator : public Base, private jsi::Instrumentation {
     return plain_.symbolToString(sym);
   }
 
+  BigInt createBigIntFromInt64(int64_t value) override {
+    return plain_.createBigIntFromInt64(value);
+  }
+  BigInt createBigIntFromUint64(uint64_t value) override {
+    return plain_.createBigIntFromUint64(value);
+  }
+  bool bigintIsInt64(const BigInt& b) override {
+    return plain_.bigintIsInt64(b);
+  }
+  bool bigintIsUint64(const BigInt& b) override {
+    return plain_.bigintIsUint64(b);
+  }
+  uint64_t truncate(const BigInt& b) override {
+    return plain_.truncate(b);
+  }
+  String bigintToString(const BigInt& bigint, int radix) override {
+    return plain_.bigintToString(bigint, radix);
+  }
+
   String createStringFromAscii(const char* str, size_t length) override {
     return plain_.createStringFromAscii(str, length);
   };

ReactCommon/jsi/jsi/jsi-inl.h

@@ -341,5 +341,9 @@ inline Value Function::callAsConstructor(Runtime& runtime, Args&&... args)
       runtime, {detail::toValue(runtime, std::forward<Args>(args))...});
 }
 
+String BigInt::toString(Runtime& runtime, int radix) const {
+  return runtime.bigintToString(*this, radix);
+}
+
 } // namespace jsi
 } // namespace facebook

ReactCommon/jsi/jsi/jsi.cpp

@@ -381,6 +381,20 @@ String Value::toString(Runtime& runtime) const {
   return toString.call(runtime, *this).getString(runtime);
 }
 
+uint64_t BigInt::asUint64(Runtime& runtime) const {
+  if (!isUint64(runtime)) {
+    throw JSError(runtime, "Lossy truncation in BigInt64::asUint64");
+  }
+  return getUint64(runtime);
+}
+
+int64_t BigInt::asInt64(Runtime& runtime) const {
+  if (!isInt64(runtime)) {
+    throw JSError(runtime, "Lossy truncation in BigInt64::asInt64");
+  }
+  return getInt64(runtime);
+}
+
 Array Array::createWithElements(
     Runtime& rt,
     std::initializer_list<Value> elements) {

ReactCommon/jsi/jsi/jsi.h

@@ -290,6 +290,13 @@ class JSI_EXPORT Runtime {
 
   virtual std::string symbolToString(const Symbol&) = 0;
 
+  virtual BigInt createBigIntFromInt64(int64_t) = 0;
+  virtual BigInt createBigIntFromUint64(uint64_t) = 0;
+  virtual bool bigintIsInt64(const BigInt&) = 0;
+  virtual bool bigintIsUint64(const BigInt&) = 0;
+  virtual uint64_t truncate(const BigInt&) = 0;
+  virtual String bigintToString(const BigInt&, int) = 0;
+
   virtual String createStringFromAscii(const char* str, size_t length) = 0;
   virtual String createStringFromUtf8(const uint8_t* utf8, size_t length) = 0;
   virtual std::string utf8(const String&) = 0;
@@ -507,6 +514,53 @@ class JSI_EXPORT BigInt : public Pointer {
   BigInt(BigInt&& other) = default;
   BigInt& operator=(BigInt&& other) = default;
 
+  /// Create a BigInt representing the signed 64-bit \p value.
+  static BigInt fromInt64(Runtime& runtime, int64_t value) {
+    return runtime.createBigIntFromInt64(value);
+  }
+
+  /// Create a BigInt representing the unsigned 64-bit \p value.
+  static BigInt fromUint64(Runtime& runtime, uint64_t value) {
+    return runtime.createBigIntFromUint64(value);
+  }
+
+  /// \return whether a === b.
+  static bool strictEquals(Runtime& runtime, const BigInt& a, const BigInt& b) {
+    return runtime.strictEquals(a, b);
+  }
+
+  /// \returns This bigint truncated to a signed 64-bit integer.
+  int64_t getInt64(Runtime& runtime) const {
+    return runtime.truncate(*this);
+  }
+
+  /// \returns Whether this bigint can be losslessly converted to int64_t.
+  bool isInt64(Runtime& runtime) const {
+    return runtime.bigintIsInt64(*this);
+  }
+
+  /// \returns This bigint truncated to a signed 64-bit integer. Throws a
+  /// JSIException if the truncation is lossy.
+  int64_t asInt64(Runtime& runtime) const;
+
+  /// \returns This bigint truncated to an unsigned 64-bit integer.
+  uint64_t getUint64(Runtime& runtime) const {
+    return runtime.truncate(*this);
+  }
+
+  /// \returns Whether this bigint can be losslessly converted to uint64_t.
+  bool isUint64(Runtime& runtime) const {
+    return runtime.bigintIsUint64(*this);
+  }
+
+  /// \returns This bigint truncated to an unsigned 64-bit integer. Throws a
+  /// JSIException if the truncation is lossy.
+  uint64_t asUint64(Runtime& runtime) const;
+
+  /// \returns this BigInt converted to a String in base \p radix. Throws a
+  /// JSIException if radix is not in the [2, 36] range.
+  inline String toString(Runtime& runtime, int radix = 10) const;
+
   friend class Runtime;
   friend class Value;
 };