gonum.org/v1/gonum@v0.14.0/mat/shadow_common.go (about)

     1  // Copyright ©2015 The Gonum Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package mat
     6  
     7  const (
     8  	// regionOverlap is the panic string used for the general case
     9  	// of a matrix region overlap between a source and destination.
    10  	regionOverlap = "mat: bad region: overlap"
    11  
    12  	// regionIdentity is the panic string used for the specific
    13  	// case of complete agreement between a source and a destination.
    14  	regionIdentity = "mat: bad region: identical"
    15  
    16  	// mismatchedStrides is the panic string used for overlapping
    17  	// data slices with differing strides.
    18  	mismatchedStrides = "mat: bad region: different strides"
    19  )
    20  
    21  // rectanglesOverlap returns whether the strided rectangles a and b overlap
    22  // when b is offset by off elements after a but has at least one element before
    23  // the end of a. off must be positive. a and b have aCols and bCols respectively.
    24  //
    25  // rectanglesOverlap works by shifting both matrices left such that the left
    26  // column of a is at 0. The column indexes are flattened by obtaining the shifted
    27  // relative left and right column positions modulo the common stride. This allows
    28  // direct comparison of the column offsets when the matrix backing data slices
    29  // are known to overlap.
    30  func rectanglesOverlap(off, aCols, bCols, stride int) bool {
    31  	if stride == 1 {
    32  		// Unit stride means overlapping data
    33  		// slices must overlap as matrices.
    34  		return true
    35  	}
    36  
    37  	// Flatten the shifted matrix column positions
    38  	// so a starts at 0, modulo the common stride.
    39  	aTo := aCols
    40  	// The mod stride operations here make the from
    41  	// and to indexes comparable between a and b when
    42  	// the data slices of a and b overlap.
    43  	bFrom := off % stride
    44  	bTo := (bFrom + bCols) % stride
    45  
    46  	if bTo == 0 || bFrom < bTo {
    47  		// b matrix is not wrapped: compare for
    48  		// simple overlap.
    49  		return bFrom < aTo
    50  	}
    51  
    52  	// b strictly wraps and so must overlap with a.
    53  	return true
    54  }