---
title: 案例Demo
description: "可通过JavaVectorHelper工具对单个文件/整个项目进行扫描，本章节基于单个文件提供对应的可向量化示例代码，示例代码片段功能是实现数组间运算并赋值，代码仅供参考。"
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---
# 案例Demo

可通过JavaVectorHelper工具对单个文件/整个项目进行扫描，本章节基于单个文件提供对应的可向量化示例代码，示例代码片段功能是实现数组间运算并赋值，代码仅供参考。

1. 扫描前源码文件如图1所示。
  图1 BpVectorReorderer.java

2. 运行BpVectorReorderer.java文件中的for循环。
  图2 改造前运行结果

3. 使用JavaVectorHelper工具，识别出代码块中加粗显示的代码，可替换为向量化代码。

```
private static boolean centroidValid(
float[] centroid, FloatVectorValues vectors, IntsRef ids, int count) throws IOException {
// recompute centroid to check the incremental calculation
float[] check = new float[centroid.length];
computeCentroid(ids, vectors, check, VectorSimilarityFunction.EUCLIDEAN);
for (int i = 0; i < check.length; ++i) {
float diff = Math.abs(check[i] - centroid[i]);
if (diff > 1e-4) {
return false;
}
}
return true;
}
private static void swapIdsAndCentroids(
IntsRef ids,
int from,
int to,
int midPoint,
FloatVectorValues vectors,
float[] leftCentroid,
float[] rightCentroid,
float[] scratch,
int count,
VectorSimilarityFunction vectorScore)
throws IOException {
assert from < to;
int[] idArr = ids.ints;
int fromId = idArr[from];
int toId = idArr[to];
// Now update the centroids, this makes things much faster than invalidating it and having to
// recompute on the next iteration.  Should be faster than full recalculation if the number of
// swaps is reasonable.
// We want the net effect to be moving "from" left->right and "to" right->left
// (1) scratch = to - from
if (count <= MAX_CENTROID_UPDATES && vectorScore == VectorSimilarityFunction.EUCLIDEAN) {
int relativeMidpoint = midPoint - ids.offset;
vectorSubtract(vectors.vectorValue(toId), vectors.vectorValue(fromId), scratch);
// we must normalize to the proper scale by accounting for the number of points contributing
// to each centroid
// left += scratch / size(left)
vectorScalarMul(1 / (float) relativeMidpoint, scratch);
VectorUtil.add(leftCentroid, scratch);
// right -= scratch / size(right)
vectorScalarMul(-relativeMidpoint / (float) (ids.length - relativeMidpoint), scratch);
VectorUtil.add(rightCentroid, scratch);
}
idArr[from] = toId;
idArr[to] = fromId;
if (count <= MAX_CENTROID_UPDATES) {
assert centroidValid(
leftCentroid, vectors, new IntsRef(idArr, ids.offset, midPoint - ids.offset), count);
assert centroidValid(
rightCentroid,
vectors,
new IntsRef(ids.ints, midPoint, ids.length - midPoint + ids.offset),
count);
}
}
/**
* Adds the second argument to the first
*
* @param u the destination
* @param v the vector to add to the destination
**/
static void vectorSubtract(float[] u, float[] v, float[] result) {
for (int i = 0; i < u.length; i++) {
result[i] = u[i] - v[i];
//可替换为向量化代码
}
}
```


4. 替换为向量化代码时，若代码中定义了变量名称，替换后会自动引入所需要的import语句和需要声明的常量语句。

```
static void vectorSubtract(float[] u, float[] v, float[] result) {
int i = 0;
//已替换为向量化代码
for (; i < FLOAT_SPECIES.loopBound(u.length); i = i + FLOAT_SPECIES.length()) {
FloatVector uVector = FloatVector.fromArray(FLOAT_SPECIES, u, i);
FloatVector vVector = FloatVector.fromArray(FLOAT_SPECIES, v, i);
uVector.sub(vVector).intoArray(result, i);
}
for (; i < u.length; i++) {
result[i] = u[i] - v[i];
}
}
```


  需要声明的常量语句：

```
private static final VectorSpecies<Float> FLOAT_SPECIES = FloatVector.SPECIES_PREFERRED;
```


  import语句：

```
import jdk.incubator.vector.VectorSpecies;
import jdk.incubator.vector.FloatVector;
```


5. 运行BpVectorReorderer.java文件中改造后的for循环。
  图3 改造后运行结果

  编译运行改造后的文件，运行结果保持不变，性能有所提升。