github.com/cockroachdb/tools@v0.0.0-20230222021103-a6d27438930d/internal/diff/lcs/labels.go (about)

     1  // Copyright 2022 The Go 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 lcs
     6  
     7  import (
     8  	"fmt"
     9  )
    10  
    11  //  For each D, vec[D] has length D+1,
    12  // and the label for (D, k) is stored in vec[D][(D+k)/2].
    13  type label struct {
    14  	vec [][]int
    15  }
    16  
    17  // Temporary checking DO NOT COMMIT true TO PRODUCTION CODE
    18  const debug = false
    19  
    20  // debugging. check that the (d,k) pair is valid
    21  // (that is, -d<=k<=d and d+k even)
    22  func checkDK(D, k int) {
    23  	if k >= -D && k <= D && (D+k)%2 == 0 {
    24  		return
    25  	}
    26  	panic(fmt.Sprintf("out of range, d=%d,k=%d", D, k))
    27  }
    28  
    29  func (t *label) set(D, k, x int) {
    30  	if debug {
    31  		checkDK(D, k)
    32  	}
    33  	for len(t.vec) <= D {
    34  		t.vec = append(t.vec, nil)
    35  	}
    36  	if t.vec[D] == nil {
    37  		t.vec[D] = make([]int, D+1)
    38  	}
    39  	t.vec[D][(D+k)/2] = x // known that D+k is even
    40  }
    41  
    42  func (t *label) get(d, k int) int {
    43  	if debug {
    44  		checkDK(d, k)
    45  	}
    46  	return int(t.vec[d][(d+k)/2])
    47  }
    48  
    49  func newtriang(limit int) label {
    50  	if limit < 100 {
    51  		// Preallocate if limit is not large.
    52  		return label{vec: make([][]int, limit)}
    53  	}
    54  	return label{}
    55  }