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 *  DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package jdk.internal.foreign;

import jdk.incubator.foreign.MemorySegment;
import jdk.internal.access.JavaNioAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.misc.Unsafe;
import jdk.internal.vm.annotation.ForceInline;

import java.nio.ByteBuffer;
import java.util.Objects;
import java.util.function.Supplier;

Implementation for heap memory segments. An heap memory segment is composed by an offset and
a base object (typically an array). To enhance performances, the access to the base object needs to feature
sharp type information, as well as sharp null-check information. For this reason, the factories for heap segments
use a lambda to implement the base object accessor, so that the type information will remain sharp (e.g.
the static compiler will generate specialized base accessor for us).
/**
 * Implementation for heap memory segments. An heap memory segment is composed by an offset and
 * a base object (typically an array). To enhance performances, the access to the base object needs to feature
 * sharp type information, as well as sharp null-check information. For this reason, the factories for heap segments
 * use a lambda to implement the base object accessor, so that the type information will remain sharp (e.g.
 * the static compiler will generate specialized base accessor for us).
 */
public class HeapMemorySegmentImpl<H> extends AbstractMemorySegmentImpl {

    private static final Unsafe UNSAFE = Unsafe.getUnsafe();
    private static final int BYTE_ARR_BASE = UNSAFE.arrayBaseOffset(byte[].class);

    final long offset;
    final Supplier<H> baseProvider;

    @ForceInline
    HeapMemorySegmentImpl(long offset, Supplier<H> baseProvider, long length, int mask, MemoryScope scope) {
        super(length, mask, scope);
        this.offset = offset;
        this.baseProvider = baseProvider;
    }

    @Override
    H base() {
        return Objects.requireNonNull(baseProvider.get());
    }

    @Override
    long min() {
        return offset;
    }

    @Override
    HeapMemorySegmentImpl<H> dup(long offset, long size, int mask, MemoryScope scope) {
        return new HeapMemorySegmentImpl<>(this.offset + offset, baseProvider, size, mask, scope);
    }

    @Override
    ByteBuffer makeByteBuffer() {
        if (!(base() instanceof byte[])) {
            throw new UnsupportedOperationException("Not an address to an heap-allocated byte array");
        }
        JavaNioAccess nioAccess = SharedSecrets.getJavaNioAccess();
        return nioAccess.newHeapByteBuffer((byte[]) base(), (int)min() - BYTE_ARR_BASE, (int) byteSize(), this);
    }

    // factories

    public static MemorySegment makeArraySegment(byte[] arr) {
        return makeHeapSegment(() -> arr, arr.length,
                Unsafe.ARRAY_BYTE_BASE_OFFSET, Unsafe.ARRAY_BYTE_INDEX_SCALE);
    }

    public static MemorySegment makeArraySegment(char[] arr) {
        return makeHeapSegment(() -> arr, arr.length,
                Unsafe.ARRAY_CHAR_BASE_OFFSET, Unsafe.ARRAY_CHAR_INDEX_SCALE);
    }

    public static MemorySegment makeArraySegment(short[] arr) {
        return makeHeapSegment(() -> arr, arr.length,
                Unsafe.ARRAY_SHORT_BASE_OFFSET, Unsafe.ARRAY_SHORT_INDEX_SCALE);
    }

    public static MemorySegment makeArraySegment(int[] arr) {
        return makeHeapSegment(() -> arr, arr.length,
                Unsafe.ARRAY_INT_BASE_OFFSET, Unsafe.ARRAY_INT_INDEX_SCALE);
    }

    public static MemorySegment makeArraySegment(long[] arr) {
        return makeHeapSegment(() -> arr, arr.length,
                Unsafe.ARRAY_LONG_BASE_OFFSET, Unsafe.ARRAY_LONG_INDEX_SCALE);
    }

    public static MemorySegment makeArraySegment(float[] arr) {
        return makeHeapSegment(() -> arr, arr.length,
                Unsafe.ARRAY_FLOAT_BASE_OFFSET, Unsafe.ARRAY_FLOAT_INDEX_SCALE);
    }

    public static MemorySegment makeArraySegment(double[] arr) {
        return makeHeapSegment(() -> arr, arr.length,
                Unsafe.ARRAY_DOUBLE_BASE_OFFSET, Unsafe.ARRAY_DOUBLE_INDEX_SCALE);
    }

    static <Z> HeapMemorySegmentImpl<Z> makeHeapSegment(Supplier<Z> obj, int length, int base, int scale) {
        int byteSize = length * scale;
        MemoryScope scope = MemoryScope.create(null, null);
        return new HeapMemorySegmentImpl<>(base, obj, byteSize, defaultAccessModes(byteSize), scope);
    }
}