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shadow.go
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shadow.go
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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
import (
"gonum.org/v1/gonum/blas/blas64"
)
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"
)
// checkOverlap returns false if the receiver does not overlap data elements
// referenced by the parameter and panics otherwise.
//
// checkOverlap methods return a boolean to allow the check call to be added to a
// boolean expression, making use of short-circuit operators.
func checkOverlap(a, b blas64.General) bool {
if cap(a.Data) == 0 || cap(b.Data) == 0 {
return false
}
off := offset(a.Data[:1], b.Data[:1])
if off == 0 {
// At least one element overlaps.
if a.Cols == b.Cols && a.Rows == b.Rows && a.Stride == b.Stride {
panic(regionIdentity)
}
panic(regionOverlap)
}
if off > 0 && len(a.Data) <= off {
// We know a is completely before b.
return false
}
if off < 0 && len(b.Data) <= -off {
// We know a is completely after b.
return false
}
if a.Stride != b.Stride {
// Too hard, so assume the worst.
panic(mismatchedStrides)
}
if off < 0 {
off = -off
a.Cols, b.Cols = b.Cols, a.Cols
}
if rectanglesOverlap(off, a.Cols, b.Cols, a.Stride) {
panic(regionOverlap)
}
return false
}
func (m *Dense) checkOverlap(a blas64.General) bool {
return checkOverlap(m.RawMatrix(), a)
}
func (m *Dense) checkOverlapMatrix(a Matrix) bool {
if m == a {
return false
}
var amat blas64.General
switch a := a.(type) {
default:
return false
case RawMatrixer:
amat = a.RawMatrix()
case RawSymmetricer:
amat = generalFromSymmetric(a.RawSymmetric())
case RawTriangular:
amat = generalFromTriangular(a.RawTriangular())
}
return m.checkOverlap(amat)
}
func (s *SymDense) checkOverlap(a blas64.General) bool {
return checkOverlap(generalFromSymmetric(s.RawSymmetric()), a)
}
func (s *SymDense) checkOverlapMatrix(a Matrix) bool {
if s == a {
return false
}
var amat blas64.General
switch a := a.(type) {
default:
return false
case RawMatrixer:
amat = a.RawMatrix()
case RawSymmetricer:
amat = generalFromSymmetric(a.RawSymmetric())
case RawTriangular:
amat = generalFromTriangular(a.RawTriangular())
}
return s.checkOverlap(amat)
}
// generalFromSymmetric returns a blas64.General with the backing
// data and dimensions of a.
func generalFromSymmetric(a blas64.Symmetric) blas64.General {
return blas64.General{
Rows: a.N,
Cols: a.N,
Stride: a.Stride,
Data: a.Data,
}
}
func (t *TriDense) checkOverlap(a blas64.General) bool {
return checkOverlap(generalFromTriangular(t.RawTriangular()), a)
}
func (t *TriDense) checkOverlapMatrix(a Matrix) bool {
if t == a {
return false
}
var amat blas64.General
switch a := a.(type) {
default:
return false
case RawMatrixer:
amat = a.RawMatrix()
case RawSymmetricer:
amat = generalFromSymmetric(a.RawSymmetric())
case RawTriangular:
amat = generalFromTriangular(a.RawTriangular())
}
return t.checkOverlap(amat)
}
// generalFromTriangular returns a blas64.General with the backing
// data and dimensions of a.
func generalFromTriangular(a blas64.Triangular) blas64.General {
return blas64.General{
Rows: a.N,
Cols: a.N,
Stride: a.Stride,
Data: a.Data,
}
}
func (v *VecDense) checkOverlap(a blas64.Vector) bool {
mat := v.mat
if cap(mat.Data) == 0 || cap(a.Data) == 0 {
return false
}
off := offset(mat.Data[:1], a.Data[:1])
if off == 0 {
// At least one element overlaps.
if mat.Inc == a.Inc && len(mat.Data) == len(a.Data) {
panic(regionIdentity)
}
panic(regionOverlap)
}
if off > 0 && len(mat.Data) <= off {
// We know v is completely before a.
return false
}
if off < 0 && len(a.Data) <= -off {
// We know v is completely after a.
return false
}
if mat.Inc != a.Inc {
// Too hard, so assume the worst.
panic(mismatchedStrides)
}
if mat.Inc == 1 || off&mat.Inc == 0 {
panic(regionOverlap)
}
return false
}
// 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
}