array-to-reversed.tq 3.17 KB
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// Copyright 2022 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

namespace array {
macro FastPackedArrayToReversed<Accessor: type, T: type>(
    implicit context: Context)(
    kind: constexpr ElementsKind, elements: FixedArrayBase,
    length: Smi): JSArray {
  // 3. Let A be ? ArrayCreate(𝔽(len)).
  const copy: FixedArrayBase =
      AllocateFixedArray(kind, SmiUntag(length), AllocationFlag::kNone);

  // 4. Let k be 0.
  let k: Smi = 0;

  // 5. Repeat, while k < len,
  while (k < length) {
    // a. Let from be ! ToString(𝔽(len - k - 1)).
    // b. Let Pk be ! ToString(𝔽(k)).
    const from = length - k - 1;

    // c. Let fromValue be ? Get(O, from).
    const fromValue: T = LoadElement<Accessor, T>(elements, from);

    // d. Perform ! CreateDataPropertyOrThrow(A, Pk, fromValue).
    StoreElement<Accessor>(copy, k, fromValue);

    // e. Set k to k + 1.
    ++k;
  }

  // 6. Return A.
  const map: Map = LoadJSArrayElementsMap(kind, LoadNativeContext(context));
  return NewJSArray(map, copy);
}

macro TryFastPackedArrayToReversed(implicit context: Context)(receiver: JSAny):
    JSArray labels Slow {
  const array: FastJSArray = Cast<FastJSArray>(receiver) otherwise Slow;

  const kind: ElementsKind = array.map.elements_kind;
  if (kind == ElementsKind::PACKED_SMI_ELEMENTS) {
    return FastPackedArrayToReversed<array::FastPackedSmiElements, Smi>(
        ElementsKind::PACKED_SMI_ELEMENTS, array.elements, array.length);
  }
  if (kind == ElementsKind::PACKED_ELEMENTS) {
    return FastPackedArrayToReversed<array::FastPackedObjectElements, JSAny>(
        ElementsKind::PACKED_ELEMENTS, array.elements, array.length);
  }
  if (kind == ElementsKind::PACKED_DOUBLE_ELEMENTS) {
    return FastPackedArrayToReversed<array::FastPackedDoubleElements, float64>(
        ElementsKind::PACKED_DOUBLE_ELEMENTS, array.elements, array.length);
  }

  goto Slow;
}

transitioning macro GenericArrayToReversed(
    context: Context, receiver: JSAny): JSAny {
  // 1. Let O be ? ToObject(this value).
  const object: JSReceiver = ToObject_Inline(context, receiver);

  // 2. Let len be ? LengthOfArrayLike(O).
  const len: Number = GetLengthProperty(object);

  // 3. Let A be ? ArrayCreate(𝔽(len)).
  const copy = ArrayCreate(len);

  // 4. Let k be 0.
  let k: Number = 0;

  // 5. Repeat, while k < len,
  while (k < len) {
    // a. Let from be ! ToString(𝔽(len - k - 1)).
    // b. Let Pk be ! ToString(𝔽(k)).
    const from: Number = len - k - 1;

    // c. Let fromValue be ? Get(object, from).
    const fromValue = GetProperty(object, from);

    // d. Perform ! CreateDataPropertyOrThrow(A, Pk, fromValue).
    FastCreateDataProperty(copy, k, fromValue);

    // e. Set k to k + 1.
    ++k;
  }

  // 6. Return A.
  return copy;
}

// https://tc39.es/proposal-change-array-by-copy/#sec-array.prototype.toReversed
transitioning javascript builtin ArrayPrototypeToReversed(
    js-implicit context: NativeContext, receiver: JSAny)(...arguments): JSAny {
  try {
    return TryFastPackedArrayToReversed(receiver) otherwise Slow;
  } label Slow {
    return GenericArrayToReversed(context, receiver);
  }
}
}