bug 1466893 - Part 2: Convert BigInt arguments to the Number constructor. r=jandem

js/src/jsnum.cpp

@@ -29,6 +29,9 @@
 #include "js/Conversions.h"
 #include "util/DoubleToString.h"
 #include "util/StringBuffer.h"
+#ifdef ENABLE_BIGINT
+#include "vm/BigIntType.h"
+#endif
 #include "vm/GlobalObject.h"
 #include "vm/JSAtom.h"
 #include "vm/JSContext.h"
@@ -487,8 +490,14 @@ Number(JSContext* cx, unsigned argc, Value* vp)
     CallArgs args = CallArgsFromVp(argc, vp);
 
     if (args.length() > 0) {
-        if (!ToNumber(cx, args[0]))
+        // BigInt proposal section 6.2, steps 2a-c.
+        if (!ToNumeric(cx, args[0]))
             return false;
+#ifdef ENABLE_BIGINT
+        if (args[0].isBigInt())
+            args[0].setNumber(BigInt::numberValue(args[0].toBigInt()));
+#endif
+        MOZ_ASSERT(args[0].isNumber());
     }
 
     if (!args.isConstructing()) {

js/src/vm/BigIntType.cpp

@@ -175,6 +175,18 @@ js::ToBigInt(JSContext* cx, HandleValue val)
     return nullptr;
 }
 
+// ES 2019 draft 6.1.6
+double
+BigInt::numberValue(BigInt* x)
+{
+    // mpz_get_d may cause a hardware overflow trap, so use
+    // mpz_get_d_2exp to get the fractional part and exponent
+    // separately.
+    signed long int exp;
+    double d = mpz_get_d_2exp(&exp, x->num_);
+    return ldexp(d, exp);
+}
+
 JSLinearString*
 BigInt::toString(JSContext* cx, BigInt* x, uint8_t radix)
 {

js/src/vm/BigIntType.h

@@ -69,6 +69,7 @@ class BigInt final : public js::gc::TenuredCell
 
     static BigInt* copy(JSContext* cx, Handle<BigInt*> x);
 
+    static double numberValue(BigInt* x);
     static JSLinearString* toString(JSContext* cx, BigInt* x, uint8_t radix);
 };