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LibJS: Implement BigInt.asIntN

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Timothy Flynn 2022-02-05 20:10:52 -05:00 • committed by Linus Groh
parent 72b3ea49d6
commit 460c2caaf7
2 changed files with 105 additions and 4 deletions
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30
Userland/Libraries/LibJS/Runtime/BigIntConstructor.cpp
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@ -5,6 +5,7 @@
*/
#include <AK/String.h>
#include <LibJS/Runtime/AbstractOperations.h>
#include <LibJS/Runtime/BigInt.h>
#include <LibJS/Runtime/BigIntConstructor.h>
#include <LibJS/Runtime/BigIntObject.h>
@ -14,6 +15,8 @@
namespace JS {
static const Crypto::SignedBigInteger BIGINT_ONE { 1 };
BigIntConstructor::BigIntConstructor(GlobalObject& global_object)
: NativeFunction(vm().names.BigInt.as_string(), *global_object.function_prototype())
{
@ -27,9 +30,8 @@ void BigIntConstructor::initialize(GlobalObject& global_object)
// 21.2.2.3 BigInt.prototype, https://tc39.es/ecma262/#sec-bigint.prototype
define_direct_property(vm.names.prototype, global_object.bigint_prototype(), 0);
// TODO: Implement these functions below and uncomment this.
// u8 attr = Attribute::Writable | Attribute::Configurable;
// define_native_function(vm.names.asIntN, as_int_n, 2, attr);
u8 attr = Attribute::Writable | Attribute::Configurable;
define_native_function(vm.names.asIntN, as_int_n, 2, attr);
// define_native_function(vm.names.asUintN, as_uint_n, 2, attr);
define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
@ -67,7 +69,27 @@ ThrowCompletionOr<Object*> BigIntConstructor::construct(FunctionObject&)
// 21.2.2.1 BigInt.asIntN ( bits, bigint ), https://tc39.es/ecma262/#sec-bigint.asintn
JS_DEFINE_NATIVE_FUNCTION(BigIntConstructor::as_int_n)
{
TODO();
// 1. Set bits to ? ToIndex(bits).
auto bits = TRY(vm.argument(0).to_index(global_object));
// 2. Set bigint to ? ToBigInt(bigint).
auto* bigint = TRY(vm.argument(1).to_bigint(global_object));
// 3. Let mod be ℝ(bigint) modulo 2^bits.
// FIXME: For large values of `bits`, this can likely be improved with a SignedBigInteger API to
// drop the most significant bits.
auto bits_shift_left = BIGINT_ONE.shift_left(bits);
auto mod = modulo(bigint->big_integer(), bits_shift_left);
// 4. If mod ≥ 2^(bits-1), return ℤ(mod - 2^bits); otherwise, return ℤ(mod).
// NOTE: Some of the below conditionals are non-standard, but are to protect SignedBigInteger from
// allocating an absurd amount of memory if `bits - 1` overflows to NumericLimits<size_t>::max.
if ((bits == 0) && (mod >= BIGINT_ONE))
return js_bigint(vm, mod.minus(bits_shift_left));
if ((bits > 0) && (mod >= BIGINT_ONE.shift_left(bits - 1)))
return js_bigint(vm, mod.minus(bits_shift_left));
return js_bigint(vm, mod);
}
// 21.2.2.2 BigInt.asUintN ( bits, bigint ), https://tc39.es/ecma262/#sec-bigint.asuintn