nova_vm 1.0.0

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

use ecmascript_atomics::Ordering;

use super::{AnyArrayBuffer, ArrayBuffer, InternalBuffer};
#[cfg(feature = "shared-array-buffer")]
use crate::ecmascript::SharedDataBlock;
use crate::{
    ecmascript::{
        Agent, BUILTIN_STRING_MEMORY, ExceptionType, Function, JsResult, Numeric, Object,
        ProtoIntrinsics, Value, Viewable, create_byte_data_block, get,
        ordinary_create_from_constructor, to_index,
    },
    engine::{Bindable, GcScope, NoGcScope},
    heap::{ArenaAccess, ArenaAccessMut},
};

// TODO: Implement the contents of the `DetachKey` struct?
#[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Ord)]
pub struct DetachKey {}

/// ### [25.1.3.1 AllocateArrayBuffer ( constructor, byteLength \[ , maxByteLength \] )](https://tc39.es/ecma262/#sec-allocatearraybuffer)
///
/// The abstract operation AllocateArrayBuffer takes arguments *constructor*
/// (a constructor) and *byteLength* (a non-negative integer) and optional
/// argument *maxByteLength* (a non-negative integer or EMPTY) and returns
/// either a normal completion containing an ArrayBuffer or a throw
/// completion. It is used to create an ArrayBuffer.
pub(crate) fn allocate_array_buffer<'a>(
    agent: &mut Agent,
    constructor: Function,
    byte_length: u64,
    max_byte_length: Option<u64>,
    mut gc: GcScope<'a, '_>,
) -> JsResult<'a, ArrayBuffer<'a>> {
    let constructor = constructor.bind(gc.nogc());
    // 1. Let slots be « [[ArrayBufferData]], [[ArrayBufferByteLength]], [[ArrayBufferDetachKey]] ».
    // 2. If maxByteLength is present and maxByteLength is not EMPTY, let allocatingResizableBuffer be true; otherwise let allocatingResizableBuffer be false.
    // 3. If allocatingResizableBuffer is true, then
    if let Some(max_byte_length) = max_byte_length {
        // a. If byteLength > maxByteLength, throw a RangeError exception.
        if byte_length > max_byte_length {
            return Err(agent.throw_exception_with_static_message(
                ExceptionType::RangeError,
                "Byte length is over maximumm byte length",
                gc.into_nogc(),
            ));
        }
        // b. Append [[ArrayBufferMaxByteLength]] to slots.
    }
    // 4. Let obj be ? OrdinaryCreateFromConstructor(constructor, "%ArrayBuffer.prototype%", slots).
    let Object::ArrayBuffer(obj) = ordinary_create_from_constructor(
        agent,
        constructor.unbind(),
        ProtoIntrinsics::ArrayBuffer,
        gc.reborrow(),
    )
    .unbind()?
    .bind(gc.nogc()) else {
        unreachable!()
    };
    let obj = obj.unbind();
    let gc = gc.into_nogc();
    let obj = obj.bind(gc);
    // 5. Let block be ? CreateByteDataBlock(byteLength).
    // 8. If allocatingResizableBuffer is true, then
    let buffer = if let Some(max_byte_length) = max_byte_length {
        // a. If it is not possible to create a Data Block block consisting of
        //    maxByteLength bytes, throw a RangeError exception.
        // b. NOTE: Resizable ArrayBuffers are designed to be implementable
        //    with in-place growth. Implementations may throw if, for example,
        //    virtual memory cannot be reserved up front.
        // c. Set obj.[[ArrayBufferMaxByteLength]] to maxByteLength.
        let mut block = create_byte_data_block(agent, max_byte_length, gc)?;
        block.realloc(byte_length as usize);
        InternalBuffer::resizable(block, max_byte_length as usize)
    } else {
        InternalBuffer::fixed_length(create_byte_data_block(agent, byte_length, gc)?)
    };
    // 6. Set obj.[[ArrayBufferData]] to block.
    // 7. Set obj.[[ArrayBufferByteLength]] to byteLength.
    obj.get_mut(agent).buffer = buffer;
    // 9. Return obj.
    Ok(obj)
}

/// ### [25.1.3.3 IsDetachedBuffer ( arrayBuffer )](https://tc39.es/ecma262/#sec-isdetachedbuffer)
///
/// The abstract operation IsDetachedBuffer takes argument *arrayBuffer* (an
/// ArrayBuffer or a SharedArrayBuffer) and returns a Boolean.
#[inline]
pub(crate) fn is_detached_buffer(agent: &Agent, array_buffer: ArrayBuffer) -> bool {
    // 1. If arrayBuffer.[[ArrayBufferData]] is null, return true.
    // 2. Return false.
    array_buffer.get(agent).is_detached()
}

/// ### [25.1.3.4 DetachArrayBuffer ( arrayBuffer \[ , key \] )](https://tc39.es/ecma262/#sec-detacharraybuffer)
///
/// The abstract operation DetachArrayBuffer takes argument *arrayBuffer* (an
/// ArrayBuffer) and optional argument *key* (anything) and returns either a
/// normal completion containing UNUSED or a throw completion.
pub(crate) fn detach_array_buffer<'a>(
    agent: &mut Agent,
    array_buffer: ArrayBuffer,
    key: Option<DetachKey>,
    gc: NoGcScope<'a, '_>,
) -> JsResult<'a, ()> {
    // 1. Assert: IsSharedArrayBuffer(arrayBuffer) is false.
    // 2. If key is not present, set key to undefined.
    // 3. If arrayBuffer.[[ArrayBufferDetachKey]] is not key, throw a TypeError exception.
    if array_buffer.get_detach_key(agent) != key {
        return Err(agent.throw_exception_with_static_message(
            ExceptionType::TypeError,
            "Mismatching array buffer detach keys",
            gc,
        ));
    }

    // 4. Set arrayBuffer.[[ArrayBufferData]] to null.
    // 5. Set arrayBuffer.[[ArrayBufferByteLength]] to 0.
    array_buffer.get_mut(agent).buffer.detach();
    // 6. Return UNUSED.
    Ok(())
}

/// ### [25.1.3.6 GetArrayBufferMaxByteLengthOption ( options )](https://tc39.es/ecma262/#sec-getarraybuffermaxbytelengthoption)
///
/// The abstract operation GetArrayBufferMaxByteLengthOption takes argument
/// options (an ECMAScript language value) and returns either a normal
/// completion containing either a non-negative integer or EMPTY, or a throw
/// completion.
pub(crate) fn get_array_buffer_max_byte_length_option<'a>(
    agent: &mut Agent,
    options: Value,
    mut gc: GcScope<'a, '_>,
) -> JsResult<'a, Option<u64>> {
    let options = options.bind(gc.nogc());
    // 1. If options is not an Object, return EMPTY.
    let options = if let Ok(options) = Object::try_from(options) {
        options
    } else {
        return Ok(None);
    };
    // 2. Let maxByteLength be ? Get(options, "maxByteLength").
    let max_byte_length = get(
        agent,
        options.unbind(),
        BUILTIN_STRING_MEMORY.maxByteLength.into(),
        gc.reborrow(),
    )
    .unbind()?
    .bind(gc.nogc());
    // 3. If maxByteLength is undefined, return EMPTY.
    if max_byte_length.is_undefined() {
        return Ok(None);
    }
    // 4. Return ? ToIndex(maxByteLength).
    Ok(Some(to_index(agent, max_byte_length.unbind(), gc)? as u64))
}

/// ### [25.1.3.8 IsFixedLengthArrayBuffer ( arrayBuffer )](https://tc39.es/ecma262/#sec-isfixedlengtharraybuffer)
///
/// The abstract operation IsFixedLengthArrayBuffer takes argument
/// arrayBuffer (an ArrayBuffer or a SharedArrayBuffer) and returns a
/// Boolean.
#[inline(always)]
pub(crate) fn is_fixed_length_array_buffer(agent: &Agent, array_buffer: AnyArrayBuffer) -> bool {
    // 1. If arrayBuffer has an [[ArrayBufferMaxByteLength]] internal slot, return false.
    // 2. Return true.
    !array_buffer.is_resizable(agent)
}

/// ### [25.1.3.13 RawBytesToNumeric ( type, rawBytes, isLittleEndian )](https://tc39.es/ecma262/#sec-rawbytestonumeric)
///
/// The abstract operation RawBytesToNumeric takes arguments type (a
/// TypedArray element type), rawBytes (a List of byte values), and
/// isLittleEndian (a Boolean) and returns a Number or a BigInt.
#[inline(always)]
pub(crate) fn raw_bytes_to_numeric<'a, T: Viewable>(
    agent: &mut Agent,
    raw_bytes: T,
    is_little_endian: bool,
    gc: NoGcScope<'a, '_>,
) -> Numeric<'a> {
    // 1. Let elementSize be the Element Size value specified in Table 71 for Element Type type.
    // 2. If isLittleEndian is false, reverse the order of the elements of rawBytes.
    // 3. If type is FLOAT32, then
    // a. Let value be the byte elements of rawBytes concatenated and interpreted as a little-endian bit string encoding of an IEEE 754-2019 binary32 value.
    // b. If value is an IEEE 754-2019 binary32 NaN value, return the NaN Number value.
    // c. Return the Number value that corresponds to value.
    // 4. If type is FLOAT64, then
    // a. Let value be the byte elements of rawBytes concatenated and interpreted as a little-endian bit string encoding of an IEEE 754-2019 binary64 value.
    // b. If value is an IEEE 754-2019 binary64 NaN value, return the NaN Number value.
    // c. Return the Number value that corresponds to value.
    // 5. If IsUnsignedElementType(type) is true, then
    // a. Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of an unsigned little-endian binary number.
    // 6. Else,
    // a. Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of a binary little-endian two's complement number of bit length elementSize × 8.
    // 7. If IsBigIntElementType(type) is true, return the BigInt value that corresponds to intValue.
    // 8. Otherwise, return the Number value that corresponds to intValue.
    if is_little_endian {
        raw_bytes.into_le_value(agent, gc)
    } else {
        raw_bytes.into_be_value(agent, gc)
    }
}

/// ### [25.1.3.14 GetRawBytesFromSharedBlock ( block, byteIndex, type, isTypedArray, order )](https://tc39.es/ecma262/#sec-getrawbytesfromsharedblock)
///
/// The abstract operation GetRawBytesFromSharedBlock takes arguments block
/// (a Shared Data Block), byteIndex (a non-negative integer), type (a
/// TypedArray element type), isTypedArray (a Boolean), and order (SEQ-CST
/// or UNORDERED) and returns a List of byte values.
#[inline(always)]
#[cfg(feature = "shared-array-buffer")]
pub(crate) fn get_raw_bytes_from_shared_block<T: Viewable>(
    block: &SharedDataBlock,
    byte_index: usize,
    is_typed_array: bool,
    order: Ordering,
) -> T {
    // 1. Let elementSize be the Element Size value specified in Table 71 for Element Type type.
    // 2. Let execution be the [[CandidateExecution]] field of the surrounding agent's Agent Record.
    // 3. Let eventsRecord be the Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] is AgentSignifier().
    // 4. If isTypedArray is true and IsNoTearConfiguration(type, order) is true, let noTear be true; otherwise let noTear be false.
    // 5. Let rawValue be a List of length elementSize whose elements are nondeterministically chosen byte values.
    // 6. NOTE: In implementations, rawValue is the result of a non-atomic or atomic read instruction on the underlying hardware. The nondeterminism is a semantic prescription of the memory model to describe observable behaviour of hardware with weak consistency.
    // 7. Let readEvent be ReadSharedMemory { [[Order]]: order, [[NoTear]]: noTear, [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize }.
    // 8. Append readEvent to eventsRecord.[[EventList]].
    // 9. Append Chosen Value Record { [[Event]]: readEvent, [[ChosenValue]]: rawValue } to execution.[[ChosenValues]].
    // 10. Return rawValue.
    if is_typed_array {
        block.load::<T>(byte_index, order).expect("Invalid GetRawBytesFromSharedBlock call: did not check index alignment and buffer length beforehand")
    } else {
        block.load_unaligned::<T>(byte_index).expect(
            "Invalid GetRawBytesFromSharedBlock call: did not check buffer length beforehand",
        )
    }
}

/// ### [25.1.3.15 GetValueFromBuffer ( arrayBuffer, byteIndex, type, isTypedArray, order \[ , isLittleEndian \] )](https://tc39.es/ecma262/#sec-getvaluefrombuffer)
///
/// The abstract operation GetValueFromBuffer takes arguments arrayBuffer
/// (an ArrayBuffer or SharedArrayBuffer), byteIndex (a non-negative
/// integer), type (a TypedArray element type), isTypedArray (a Boolean),
/// and order (SEQ-CST or UNORDERED) and optional argument isLittleEndian
/// (a Boolean) and returns a Number or a BigInt.
pub(crate) fn get_value_from_buffer<'a, T: Viewable>(
    agent: &mut Agent,
    array_buffer: AnyArrayBuffer,
    byte_index: usize,
    is_typed_array: bool,
    order: Ordering,
    is_little_endian: Option<bool>,
    gc: NoGcScope<'a, '_>,
) -> Numeric<'a> {
    // 1. Assert: IsDetachedBuffer(arrayBuffer) is false.
    debug_assert!(!array_buffer.is_detached(agent));
    // 2. Assert: There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.
    // 4. Let elementSize be the Element Size value specified in Table 71 for Element Type type.
    let raw_value = match array_buffer {
        // 5. If IsSharedArrayBuffer(arrayBuffer) is true, then
        #[cfg(feature = "shared-array-buffer")]
        AnyArrayBuffer::SharedArrayBuffer(sab) => {
            // 3. Let block be arrayBuffer.[[ArrayBufferData]].
            let block = sab.get_data_block(agent);
            // a. Assert: block is a Shared Data Block.
            // b. Let rawValue be GetRawBytesFromSharedBlock(block, byteIndex, type,
            //    isTypedArray, order).
            get_raw_bytes_from_shared_block::<T>(block, byte_index, is_typed_array, order)
        }
        // 6. Else,
        AnyArrayBuffer::ArrayBuffer(ab) => {
            let _ = order;
            // 3. Let block be arrayBuffer.[[ArrayBufferData]].
            let block = ab.get(agent).get_data_block();
            // a. Let rawValue be a List whose elements are bytes from block at indices
            //    in the interval from byteIndex (inclusive) to byteIndex + elementSize
            //    (exclusive).
            if is_typed_array {
                // SAFETY: Caller checked.
                unsafe { block.read_aligned(byte_index) }
            } else {
                // SAFETY: Caller checked.
                unsafe { block.read_unaligned(byte_index) }
            }
        }
    };
    // 7. Assert: The number of elements in rawValue is elementSize.
    // 8. If isLittleEndian is not present, set isLittleEndian to the value of
    //    the [[LittleEndian]] field of the surrounding agent's Agent Record.
    let is_little_endian = is_little_endian.unwrap_or({
        #[cfg(target_endian = "little")]
        {
            true
        }
        #[cfg(target_endian = "big")]
        {
            false
        }
    });

    // 9. Return RawBytesToNumeric(type, rawValue, isLittleEndian).
    raw_bytes_to_numeric::<T>(agent, raw_value, is_little_endian, gc)
}

/// ### [25.1.3.16 NumericToRawBytes ( type, value, isLittleEndian )](https://tc39.es/ecma262/#sec-numerictorawbytes)
///
/// The abstract operation NumericToRawBytes takes arguments type (a
/// TypedArray element type), value (a Number or a BigInt), and
/// isLittleEndian (a Boolean) and returns a List of byte values.
pub(crate) fn numeric_to_raw_bytes<T: Viewable>(
    agent: &mut Agent,
    value: Numeric,
    is_little_endian: bool,
) -> T {
    // 1. If type is FLOAT32, then
    // a. Let rawBytes be a List whose elements are the 4 bytes that are the result of converting value to IEEE 754-2019 binary32 format using roundTiesToEven mode. The bytes are arranged in little endian order. If value is NaN, rawBytes may be set to any implementation chosen IEEE 754-2019 binary32 format Not-a-Number encoding. An implementation must always choose the same encoding for each implementation distinguishable NaN value.
    // 2. Else if type is FLOAT64, then
    // a. Let rawBytes be a List whose elements are the 8 bytes that are the IEEE 754-2019 binary64 format encoding of value. The bytes are arranged in little endian order. If value is NaN, rawBytes may be set to any implementation chosen IEEE 754-2019 binary64 format Not-a-Number encoding. An implementation must always choose the same encoding for each implementation distinguishable NaN value.
    // 3. Else,
    // a. Let n be the Element Size value specified in Table 71 for Element Type type.
    // b. Let convOp be the abstract operation named in the Conversion Operation column in Table 71 for Element Type type.
    // c. Let intValue be ℝ(convOp(value)).
    // d. If intValue ≥ 0, then
    // i. Let rawBytes be a List whose elements are the n-byte binary encoding of intValue. The bytes are ordered in little endian order.
    // e. Else,
    // i. Let rawBytes be a List whose elements are the n-byte binary two's complement encoding of intValue. The bytes are ordered in little endian order.
    // 4. If isLittleEndian is false, reverse the order of the elements of rawBytes.
    // 5. Return rawBytes.
    if is_little_endian {
        T::from_le_value(agent, value)
    } else {
        T::from_be_value(agent, value)
    }
}

/// ### [25.1.3.17 SetValueInBuffer ( arrayBuffer, byteIndex, type, value, isTypedArray, order \[ , isLittleEndian \] )](https://tc39.es/ecma262/#sec-setvalueinbuffer)
///
/// The abstract operation SetValueInBuffer takes arguments arrayBuffer (an
/// ArrayBuffer or SharedArrayBuffer), byteIndex (a non-negative integer),
/// type (a TypedArray element type), value (a Number or a BigInt),
/// isTypedArray (a Boolean), and order (SEQ-CST, UNORDERED, or INIT) and
/// optional argument isLittleEndian (a Boolean) and returns UNUSED.
#[allow(clippy::too_many_arguments)]
pub(crate) fn set_value_in_buffer<T: Viewable>(
    agent: &mut Agent,
    array_buffer: AnyArrayBuffer,
    byte_index: usize,
    value: Numeric,
    is_typed_array: bool,
    order: Ordering,
    is_little_endian: Option<bool>,
) {
    // 1. Assert: IsDetachedBuffer(arrayBuffer) is false.
    debug_assert!(!array_buffer.is_detached(agent));
    // 2. Assert: There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.
    // 3. Assert: value is a BigInt if IsBigIntElementType(type) is true; otherwise, value is a Number.

    // 5. Let elementSize be the Element Size value specified in Table 71 for Element Type type.
    // 6. If isLittleEndian is not present, set isLittleEndian to the value of the [[LittleEndian]] field of the surrounding agent's Agent Record.
    let is_little_endian = is_little_endian.unwrap_or({
        #[cfg(target_endian = "little")]
        {
            true
        }
        #[cfg(target_endian = "big")]
        {
            false
        }
    });

    // 7. Let rawBytes be NumericToRawBytes(type, value, isLittleEndian).
    let raw_bytes = numeric_to_raw_bytes::<T>(agent, value, is_little_endian);
    match array_buffer {
        // 8. If IsSharedArrayBuffer(arrayBuffer) is true, then
        #[cfg(feature = "shared-array-buffer")]
        AnyArrayBuffer::SharedArrayBuffer(sab) => {
            // 4. Let block be arrayBuffer.[[ArrayBufferData]].
            let block = sab.get_data_block(agent);
            // a. Let execution be the [[CandidateExecution]] field of the surrounding agent's Agent Record.
            // b. Let eventsRecord be the Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] is AgentSignifier().
            // c. If isTypedArray is true and IsNoTearConfiguration(type, order) is true, let noTear be true; otherwise let noTear be false.
            // d. Append WriteSharedMemory { [[Order]]: order, [[NoTear]]: noTear, [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize, [[Payload]]: rawBytes } to eventsRecord.[[EventList]].
            if is_typed_array {
                block
                    .store::<T>(byte_index, raw_bytes, order)
                    .expect("Unaligned store or SharedDataBlock not large enough")
            } else {
                block
                    .store_unaligned::<T>(byte_index, raw_bytes)
                    .expect("SharedDataBlock not large enough")
            }
        }
        // 9. Else,
        AnyArrayBuffer::ArrayBuffer(ab) => {
            let _ = order;
            let _ = is_typed_array;
            // 4. Let block be arrayBuffer.[[ArrayBufferData]].
            let block = ab.get_mut(agent).get_data_block_mut();
            // a. Store the individual bytes of rawBytes into block, starting at block[byteIndex].
            block.set_offset_by_byte::<T>(byte_index, raw_bytes);
        }
    }

    // 10. Return UNUSED.
}

/// ### [25.1.3.18 GetModifySetValueInBuffer ( arrayBuffer, byteIndex, type, value, op )](https://tc39.es/ecma262/#sec-getmodifysetvalueinbuffer)
///
/// The abstract operation GetModifySetValueInBuffer takes arguments
/// arrayBuffer (an ArrayBuffer or a SharedArrayBuffer), byteIndex (a
/// non-negative integer), type (a TypedArray element type), value (a Number or
/// a BigInt), and op (a read-modify-write modification function) and returns a
/// Number or a BigInt.
#[cfg(feature = "atomics")]
pub(crate) fn get_modify_set_value_in_buffer<'gc, Type: Viewable, const OP: u8>(
    agent: &mut Agent,
    array_buffer: AnyArrayBuffer,
    byte_index: usize,
    value: Numeric,
    gc: NoGcScope<'gc, '_>,
) -> Numeric<'gc> {
    // 5. Let elementSize be the Element Size value specified in Table
    //    71 for Element Type type.
    let element_size = size_of::<Type>();

    // 1. Assert: IsDetachedBuffer(arrayBuffer) is false.
    debug_assert!(!array_buffer.is_detached(agent));
    // 2. Assert: There are sufficient bytes in arrayBuffer starting at
    //    byteIndex to represent a value of type.
    debug_assert!(
        byte_index + size_of::<Type>() <= array_buffer.byte_length(agent, Ordering::Unordered)
    );
    // 3. Assert: value is a BigInt if IsBigIntElementType(type) is true;
    //    otherwise, value is a Number.
    debug_assert!(value.is_bigint() == Type::IS_BIGINT);
    // 6. Let isLittleEndian be the value of the [[LittleEndian]] field
    //    of the surrounding agent's Agent Record.
    // 7. Let rawBytes be NumericToRawBytes(type, value, isLittleEndian).
    let raw_bytes = Type::from_ne_value(agent, value);
    let raw_bytes_read = match array_buffer {
        AnyArrayBuffer::ArrayBuffer(array_buffer) => {
            let op = get_array_buffer_op::<Type, OP>();
            // 4. Let block be arrayBuffer.[[ArrayBufferData]].
            let block = array_buffer.as_mut_slice(agent);
            // 8. If IsSharedArrayBuffer(arrayBuffer) is true, then
            // 9. Else,
            let slot = &mut block[byte_index..byte_index + element_size];
            // SAFETY: Viewable types are safe to transmute.
            let (head, slot, tail) = unsafe { slot.align_to_mut::<Type>() };
            debug_assert!(head.is_empty() && tail.is_empty());
            // a. Let rawBytesRead be a List of length elementSize whose
            //    elements are the sequence of elementSize bytes starting with
            //    block[byteIndex].
            let raw_bytes_read = slot[0];
            // b. Let rawBytesModified be op(rawBytesRead, rawBytes).
            let data_modified = op(raw_bytes_read, raw_bytes);
            // c. Store the individual bytes of rawBytesModified into block,
            //    starting at block[byteIndex].
            slot[0] = data_modified;
            raw_bytes_read
        }
        AnyArrayBuffer::SharedArrayBuffer(array_buffer) => {
            // 8. If IsSharedArrayBuffer(arrayBuffer) is true, then
            let buffer = array_buffer.as_slice(agent);
            let slot = buffer.slice(byte_index, byte_index + element_size);
            let (head, slot, tail) = slot.align_to::<Type::Storage>();
            debug_assert!(head.is_empty() && tail.is_empty());
            let slot = slot.get(0).unwrap();
            let result = if const { OP == 0 } {
                // Add
                let raw_bytes = Type::into_storage(raw_bytes);
                slot.fetch_add(raw_bytes)
            } else if const { OP == 1 } {
                // And
                let raw_bytes = Type::into_storage(raw_bytes);
                slot.fetch_and(raw_bytes)
            } else if const { OP == 2 } {
                // Exchange
                let raw_bytes = Type::into_storage(raw_bytes);
                slot.swap(raw_bytes)
            } else if const { OP == 3 } {
                // Or
                let raw_bytes = Type::into_storage(raw_bytes);
                slot.fetch_or(raw_bytes)
            } else if const { OP == 4 } {
                // Sub
                let raw_bytes = raw_bytes.neg();
                let raw_bytes = Type::into_storage(raw_bytes);
                slot.fetch_add(raw_bytes)
            } else if const { OP == 5 } {
                // Xor
                let raw_bytes = Type::into_storage(raw_bytes);
                slot.fetch_xor(raw_bytes)
            } else {
                panic!("Unsupported Op value");
            };
            // a. Let execution be the [[CandidateExecution]] field of the
            //    surrounding agent's Agent Record.
            // b. Let eventsRecord be the Agent Events Record of
            //    execution.[[EventsRecords]] whose [[AgentSignifier]] is
            //    AgentSignifier().
            // c. Let rawBytesRead be a List of length elementSize whose
            //    elements are nondeterministically chosen byte values.
            // d. NOTE: In implementations, rawBytesRead is the result of a
            //    load-link, of a load-exclusive, or of an operand of a
            //    read-modify-write instruction on the underlying hardware. The
            //    nondeterminism is a semantic prescription of the memory model
            //    to describe observable behaviour of hardware with weak
            //    consistency.
            // e. Let rmwEvent be ReadModifyWriteSharedMemory { .. }.
            // f. Append rmwEvent to eventsRecord.[[EventList]].
            // g. Append Chosen Value Record { [[Event]]: rmwEvent,
            //    [[ChosenValue]]: rawBytesRead } to execution.[[ChosenValues]].
            Type::from_storage(result)
        }
    };
    // 10. Return RawBytesToNumeric(type, rawBytesRead, isLittleEndian).
    raw_bytes_read.into_ne_value(agent, gc)
}

#[cfg(feature = "atomics")]
type ModifyOp<T> = fn(T, T) -> T;

#[cfg(feature = "atomics")]
const fn get_array_buffer_op<T: Viewable, const OP: u8>() -> ModifyOp<T> {
    if const { OP == 0 } {
        // Add
        <T as Viewable>::add
    } else if const { OP == 1 } {
        // And
        <T as Viewable>::and
    } else if const { OP == 2 } {
        // Exchange
        <T as Viewable>::swap
    } else if const { OP == 3 } {
        // Or
        <T as Viewable>::or
    } else if const { OP == 4 } {
        // Sub
        <T as Viewable>::sub
    } else if const { OP == 5 } {
        // Xor
        <T as Viewable>::xor
    } else {
        panic!("Unsupported Op value");
    }
}

#[cfg(feature = "atomics")]
pub(crate) fn compare_exchange_in_buffer<'gc, Type: Viewable>(
    agent: &mut Agent,
    array_buffer: AnyArrayBuffer,
    byte_index: usize,
    expected: Numeric,
    replacement: Numeric,
    gc: NoGcScope<'gc, '_>,
) -> Numeric<'gc> {
    // 5. Let elementSize be the Element Size value specified in Table
    //    71 for Element Type type.
    let element_size = size_of::<Type>();

    // 1. Assert: IsDetachedBuffer(arrayBuffer) is false.
    debug_assert!(!array_buffer.is_detached(agent));
    // 2. Assert: There are sufficient bytes in arrayBuffer starting at
    //    byteIndex to represent a value of type.
    debug_assert!(
        byte_index + size_of::<Type>() <= array_buffer.byte_length(agent, Ordering::Unordered)
    );
    // 3. Assert: value is a BigInt if IsBigIntElementType(type) is true;
    //    otherwise, value is a Number.
    debug_assert!(
        expected.is_bigint() == Type::IS_BIGINT && replacement.is_bigint() == Type::IS_BIGINT
    );
    // 10. Let isLittleEndian be AR.[[LittleEndian]].
    // 11. Let expectedBytes be
    //     NumericToRawBytes(elementType, expected, isLittleEndian).
    let expected_bytes = Type::from_ne_value(agent, expected);
    // 12. Let replacementBytes be
    //     NumericToRawBytes(elementType, replacement, isLittleEndian).
    let replacement_bytes = Type::from_ne_value(agent, replacement);
    let raw_bytes_read = match array_buffer {
        // 13. If IsSharedArrayBuffer(buffer) is true, then
        AnyArrayBuffer::SharedArrayBuffer(array_buffer) => {
            let buffer = array_buffer.as_slice(agent);
            let slot = buffer.slice(byte_index, byte_index + element_size);
            let (head, slot, tail) = slot.align_to::<Type::Storage>();
            debug_assert!(head.is_empty() && tail.is_empty());
            let slot = slot.get(0).unwrap();
            // a. Let rawBytesRead be
            //    AtomicCompareExchangeInSharedBlock(block, byteIndexInBuffer,
            //    elementSize, expectedBytes, replacementBytes).
            let expected_bytes = Type::into_storage(expected_bytes);
            let replacement_bytes = Type::into_storage(replacement_bytes);
            match slot.compare_exchange(expected_bytes, replacement_bytes) {
                Ok(r) => Type::from_storage(r),
                Err(r) => Type::from_storage(r),
            }
        }
        // 14. Else,
        AnyArrayBuffer::ArrayBuffer(array_buffer) => {
            // 3. Let block be buffer.[[ArrayBufferData]].
            let block = array_buffer.as_mut_slice(agent);
            let slot = &mut block[byte_index..byte_index + element_size];
            // SAFETY: Viewable types are safe to transmute.
            let (head, slot, tail) = unsafe { slot.align_to_mut::<Type>() };
            debug_assert!(head.is_empty() && tail.is_empty());
            // a. Let rawBytesRead be a List of length elementSize whose
            //    elements are the sequence of elementSize bytes starting with
            //    block[byteIndexInBuffer].
            let raw_bytes_read = slot[0];
            // b. If ByteListEqual(rawBytesRead, expectedBytes) is true, then
            if raw_bytes_read == expected_bytes {
                // i. Store the individual bytes of replacementBytes into
                //    block, starting at block[byteIndexInBuffer].
                slot[0] = replacement_bytes;
            }
            raw_bytes_read
        }
    };
    // 15. Return RawBytesToNumeric(elementType, rawBytesRead, isLittleEndian).
    raw_bytes_read.into_ne_value(agent, gc)
}