55 lines
1.9 KiB
Go
55 lines
1.9 KiB
Go
// Copyright ©2015 The Gonum Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package mat
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const (
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// regionOverlap is the panic string used for the general case
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// of a matrix region overlap between a source and destination.
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regionOverlap = "mat: bad region: overlap"
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// regionIdentity is the panic string used for the specific
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// case of complete agreement between a source and a destination.
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regionIdentity = "mat: bad region: identical"
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// mismatchedStrides is the panic string used for overlapping
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// data slices with differing strides.
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mismatchedStrides = "mat: bad region: different strides"
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)
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// rectanglesOverlap returns whether the strided rectangles a and b overlap
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// when b is offset by off elements after a but has at least one element before
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// the end of a. off must be positive. a and b have aCols and bCols respectively.
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//
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// rectanglesOverlap works by shifting both matrices left such that the left
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// column of a is at 0. The column indexes are flattened by obtaining the shifted
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// relative left and right column positions modulo the common stride. This allows
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// direct comparison of the column offsets when the matrix backing data slices
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// are known to overlap.
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func rectanglesOverlap(off, aCols, bCols, stride int) bool {
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if stride == 1 {
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// Unit stride means overlapping data
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// slices must overlap as matrices.
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return true
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}
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// Flatten the shifted matrix column positions
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// so a starts at 0, modulo the common stride.
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aTo := aCols
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// The mod stride operations here make the from
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// and to indexes comparable between a and b when
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// the data slices of a and b overlap.
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bFrom := off % stride
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bTo := (bFrom + bCols) % stride
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if bTo == 0 || bFrom < bTo {
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// b matrix is not wrapped: compare for
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// simple overlap.
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return bFrom < aTo
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}
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// b strictly wraps and so must overlap with a.
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return true
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}
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