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