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Eliminating tail recursion in JBDiff#split
Previously, on large-ish files, JBDiff#split would sometimes cause StackOverflowExceptions due to the use of tail recursion. Changed to use stacks to maintain state during iteration, and eliminated the recursion. Also updating variable names to be more readable. (cherry picked from commit 59aee5d)
This commit is contained in:
Joe Baker-Malone
committed by
Dana Dahlstrom
Dana Dahlstrom
parent
cede96c721
commit
aa2cd6f4d4
@@ -32,6 +32,7 @@ import com.intellij.updater.Utils.OpenByteArrayOutputStream;
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import java.io.*;
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import java.nio.charset.StandardCharsets;
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import java.util.Stack;
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import java.util.zip.GZIPOutputStream;
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/**
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@@ -51,105 +52,117 @@ public class JBDiff {
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private static final String VERSION = "jbdiff-0.1.1";
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private static final int min(int x, int y) {
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private static int min(int x, int y) {
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return x < y ? x : y;
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}
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private final static void split(int[] I, int[] V, int start, int len, int h) {
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int i, j, k, x, tmp, jj, kk;
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if (len < 16) {
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for (k = start; k < start + len; k += j) {
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j = 1;
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x = V[I[k] + h];
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for (i = 1; k + i < start + len; i++) {
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if (V[I[k + i] + h] < x) {
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x = V[I[k + i] + h];
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j = 0;
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}
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if (V[I[k + i] + h] == x) {
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tmp = I[k + j];
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I[k + j] = I[k + i];
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I[k + i] = tmp;
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j++;
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}
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private static void selectSplit(int[] I, int[] V, int start, int len, int h) {
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int j;
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for (int k = start; k < start + len; k += j) {
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j = 1;
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int x = V[I[k] + h];
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for (int i = 1; k + i < start + len; i++) {
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if (V[I[k + i] + h] < x) {
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x = V[I[k + i] + h];
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j = 0;
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}
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for (i = 0; i < j; i++) {
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V[I[k + i]] = k + j - 1;
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}
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if (j == 1) {
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I[k] = -1;
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if (V[I[k + i] + h] == x) {
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int tmp = I[k + j];
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I[k + j] = I[k + i];
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I[k + i] = tmp;
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j++;
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}
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}
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return;
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}
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x = V[I[start + len / 2] + h];
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jj = 0;
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kk = 0;
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for (i = start; i < start + len; i++) {
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if (V[I[i] + h] < x) {
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jj++;
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for (int i = 0; i < j; i++) {
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V[I[k + i]] = k + j - 1;
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}
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if (V[I[i] + h] == x) {
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kk++;
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if (j == 1) {
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I[k] = -1;
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}
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}
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}
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jj += start;
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kk += jj;
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private static void split(int[] I, int[] V, int initstart, int initlen, int h) {
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Stack<Integer> startStack = new Stack<Integer>();
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Stack<Integer> lenStack = new Stack<Integer>();
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startStack.push(initstart);
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lenStack.push(initlen);
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while (!startStack.isEmpty()) {
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int start = startStack.pop();
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int len = lenStack.pop();
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i = start;
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j = 0;
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k = 0;
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while (i < jj) {
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if (V[I[i] + h] < x) {
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i++;
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if (len < 16) {
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selectSplit(I, V, start, len, h);
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continue;
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}
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else if (V[I[i] + h] == x) {
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tmp = I[i];
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I[i] = I[jj + j];
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I[jj + j] = tmp;
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j++;
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int pivot = V[I[start + len / 2] + h];
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int endLessThanIndex = 0;
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int endLessOrEqualIndex = 0;
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for (int i = start; i < start + len; i++) {
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if (V[I[i] + h] < pivot) {
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endLessThanIndex++;
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}
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if (V[I[i] + h] == pivot) {
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endLessOrEqualIndex++;
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}
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}
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else {
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tmp = I[i];
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I[i] = I[kk + k];
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I[kk + k] = tmp;
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k++;
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endLessThanIndex += start;
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endLessOrEqualIndex += endLessThanIndex;
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int i = start;
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int currentEqualIndex = 0;
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int currentGreaterIndex = 0;
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while (i < endLessThanIndex) {
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if (V[I[i] + h] < pivot) {
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i++;
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}
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else if (V[I[i] + h] == pivot) {
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int tmp = I[i];
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I[i] = I[endLessThanIndex + currentEqualIndex];
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I[endLessThanIndex + currentEqualIndex] = tmp;
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currentEqualIndex++;
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}
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else {
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int tmp = I[i];
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I[i] = I[endLessOrEqualIndex + currentGreaterIndex];
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I[endLessOrEqualIndex + currentGreaterIndex] = tmp;
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currentGreaterIndex++;
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}
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}
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}
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while (jj + j < kk) {
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if (V[I[jj + j] + h] == x) {
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j++;
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while (endLessThanIndex + currentEqualIndex < endLessOrEqualIndex) {
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if (V[I[endLessThanIndex + currentEqualIndex] + h] == pivot) {
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currentEqualIndex++;
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}
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else {
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int tmp = I[endLessThanIndex + currentEqualIndex];
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I[endLessThanIndex + currentEqualIndex] = I[endLessOrEqualIndex + currentGreaterIndex];
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I[endLessOrEqualIndex + currentGreaterIndex] = tmp;
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currentGreaterIndex++;
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}
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}
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else {
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tmp = I[jj + j];
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I[jj + j] = I[kk + k];
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I[kk + k] = tmp;
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k++;
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for (i = endLessThanIndex; i < endLessOrEqualIndex; i++) {
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V[I[i]] = endLessOrEqualIndex - 1;
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}
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}
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if (jj > start) {
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split(I, V, start, jj - start, h);
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}
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if (endLessThanIndex == endLessOrEqualIndex - 1) {
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I[endLessThanIndex] = -1;
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}
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for (i = 0; i < kk - jj; i++) {
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V[I[jj + i]] = kk - 1;
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}
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if (endLessThanIndex > start) {
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startStack.push(start);
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lenStack.push(endLessThanIndex - start);
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}
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if (jj == kk - 1) {
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I[jj] = -1;
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}
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if (start + len > kk) {
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split(I, V, kk, start + len - kk, h);
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if (start + len > endLessOrEqualIndex) {
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startStack.push(endLessOrEqualIndex);
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lenStack.push(start + len - endLessOrEqualIndex);
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}
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}
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}
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