95 lines
2.5 KiB
C
95 lines
2.5 KiB
C
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#include <c10/util/Exception.h>
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#include <utility>
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namespace at {
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/*
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[collapse dims] Updates sizes, and strides to reflect a "collapse" of
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the info, possibly excluding the optional excludeDim. A "collapsed" version
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of the info is the fewest dims that order the tensor's elements in the same
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way as the original info. If excludeDim is specified, the collapse is the
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fewest dims that order the tensor's elements as the original and preserve the
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excluded dimension, unless the tensor collapses to a point.
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This function returns a pair of values.
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1) The (new) index of the preserved dimension if excludeDim is
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specified. 0 if the tensor is collapsed to a point. -1
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otherwise.
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2) The new number of dimensions.
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*/
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template <typename T>
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inline std::pair<int64_t, int64_t> collapse_dims(
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T* sizes,
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T* strides,
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int64_t dims,
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const int excludeDim = -1) {
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TORCH_CHECK(
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excludeDim >= -1 && excludeDim < dims,
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"expected excluded dim between -1 and dims - 1");
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int64_t stopDim = (excludeDim == -1) ? dims : excludeDim;
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int64_t newIndex = -1;
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int64_t oldIndex = 0;
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int64_t remappedExcludedDim = -1;
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while (oldIndex < dims) {
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// Finds a dimension to collapse into
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for (; oldIndex < stopDim; ++oldIndex) {
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if (sizes[oldIndex] == 1) {
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continue;
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}
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++newIndex;
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sizes[newIndex] = sizes[oldIndex];
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strides[newIndex] = strides[oldIndex];
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++oldIndex;
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break;
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}
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// Collapses dims
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for (; oldIndex < stopDim; ++oldIndex) {
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if (sizes[oldIndex] == 1) {
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continue;
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}
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if (strides[newIndex] == sizes[oldIndex] * strides[oldIndex]) {
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sizes[newIndex] *= sizes[oldIndex];
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strides[newIndex] = strides[oldIndex];
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} else {
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++newIndex;
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sizes[newIndex] = sizes[oldIndex];
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strides[newIndex] = strides[oldIndex];
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}
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}
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// Handles excludeDim being set (oldIndex == excludeDim)
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if (oldIndex != dims) {
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// Preserves excluded dimension
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++newIndex;
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sizes[newIndex] = sizes[oldIndex];
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strides[newIndex] = strides[oldIndex];
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remappedExcludedDim = newIndex;
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// Restarts iteration after excludeDim
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++oldIndex;
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stopDim = dims;
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}
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}
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// Handles special case of all dims size 1
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if (newIndex == -1 || (newIndex == 0 && sizes[0] == 1)) {
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dims = 1;
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sizes[0] = 1;
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strides[0] = 1;
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return std::pair<int64_t, int64_t>(0, 1);
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}
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dims = newIndex + 1;
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return std::pair<int64_t, int64_t>(remappedExcludedDim, dims);
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}
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} // namespace at
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