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package com.yahoo.tensor;
/**
* Utility class for efficient access and iteration along dimensions in Indexed tensors.
* Usage: Use setIndex to lock the indexes of the dimensions that don't change in this iteration.
* long base = addr.getDirectIndex();
* long stride = addr.getStride(dimension)
* i = 0...size_of_dimension
* double value = tensor.get(base + i * stride);
*
* @author baldersheim
*/
public final class DirectIndexedAddress {
private final DimensionSizes sizes;
private final int[] indexes;
private long directIndex;
private DirectIndexedAddress(DimensionSizes sizes) {
this.sizes = sizes;
indexes = new int[sizes.dimensions()];
directIndex = 0;
}
static DirectIndexedAddress of(DimensionSizes sizes) {
return new DirectIndexedAddress(sizes);
}
/** Sets the current index of a dimension */
public void setIndex(int dimension, int index) {
if (index < 0 || index >= sizes.size(dimension)) {
throw new IndexOutOfBoundsException("Index " + index + " outside of [0," + sizes.size(dimension) + ">");
}
int diff = index - indexes[dimension];
directIndex += getStride(dimension) * diff;
indexes[dimension] = index;
}
/** Retrieve the index that can be used for direct lookup in an indexed tensor. */
public long getDirectIndex() { return directIndex; }
/** returns the stride to be used for the given dimension */
public long getStride(int dimension) {
return sizes.productOfDimensionsAfter(dimension);
}
}
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