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/*
* Copyright 2023 The original authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package dev.morling.onebrc;
import java.io.IOException;
import java.util.Arrays;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
import java.lang.Math;
public class CalculateAverage_netrunnereve {
private static final String FILE = "./measurements.txt";
private static class MeasurementAggregator { // min, max, sum stored as 0.1/unit
private MeasurementAggregator next = null; // linked list of entries for handling hash colisions
private byte[] station = null;
private int min = Integer.MAX_VALUE;
private int max = Integer.MIN_VALUE;
private long sum = 0;
private int count = 0;
}
// djb2 hash
private static int calc_hash(byte[] input, int len) {
int hash = 5831;
for (int i = 0; i < len; i++) {
hash = ((hash << 5) + hash) + Byte.toUnsignedInt(input[i]);
}
return Math.abs(hash % 16384);
}
public static void main(String[] args) {
try {
RandomAccessFile mraf = new RandomAccessFile(FILE, "r");
long fileSize = mraf.getChannel().size();
long bufSize = Integer.MAX_VALUE; // Java requirement is <= Integer.MAX_VALUE
int numStations = 0;
MeasurementAggregator[] hashSpace = new MeasurementAggregator[16384]; // 14-bit hash
byte[] scratch = new byte[100]; // <= 100 characters in station name
String[] staArr = new String[10000]; // max 10000 station names
MeasurementAggregator ma = null;
long h = 0;
while (h < fileSize) {
long length = bufSize;
boolean finished = false;
if (h + length > fileSize) {
length = fileSize - h;
finished = true;
}
MappedByteBuffer mbuf = mraf.getChannel().map(FileChannel.MapMode.READ_ONLY, h, length);
int mbs = mbuf.capacity();
// check for last newline and split there, anything after goes to next buffer
if (!finished) {
for (int i = mbs - 1; true; i--) {
byte cur = mbuf.get(i - 1);
if (cur == 10) { // \n
mbs = i;
break;
}
}
}
boolean state = false; // 0 for station pickup, 1 for measurement pickup
int negMul = 1;
int head = 0;
int tempCnt = -1; // 0 if 1 digit measurement, 1 if 2 digit
for (int i = 0; i < mbs; i++) {
byte cur = mbuf.get(i);
if (state == true) {
if (cur == 46) { // .
int tempa = mbuf.get(i + 1) - 48;
tempa += (scratch[0] - 48) * (10 + 90 * tempCnt) + (scratch[1] - 48) * (10 * tempCnt); // branchless
tempa *= negMul;
if (tempa < ma.min) {
ma.min = tempa;
}
if (tempa > ma.max) {
ma.max = tempa;
}
ma.sum += tempa;
ma.count++;
i += 2; // go to start of new line
state = false;
negMul = 1;
head = i + 1;
tempCnt = -1;
}
else if (cur == 45) { // ascii -
negMul = -1;
}
else {
scratch[tempCnt + 1] = cur;
tempCnt++;
}
}
else if (cur == 59) { // ;
int len = i - head;
// this is faster than filling scratch immediately after each byte is read
mbuf.position(head);
mbuf.get(scratch, 0, len);
int hash = calc_hash(scratch, len);
ma = hashSpace[hash];
MeasurementAggregator prev = null;
while (true) {
if (ma == null) {
ma = new MeasurementAggregator();
ma.station = Arrays.copyOfRange(scratch, 0, len);
staArr[numStations] = new String(scratch, 0, len, StandardCharsets.UTF_8);
if (prev != null) {
prev.next = ma;
}
else {
hashSpace[hash] = ma;
}
numStations++;
break;
}
else if ((len != ma.station.length) || (Arrays.compare(scratch, 0, len, ma.station, 0, len) != 0)) { // hash collision
prev = ma;
ma = ma.next;
}
else { // hit
break;
}
}
state = true;
head = i + 1;
}
}
h += mbs;
}
Arrays.sort(staArr, 0, numStations);
String out = "{";
for (int i = 0; i < numStations; i++) {
byte[] strBuf = staArr[i].getBytes(StandardCharsets.UTF_8);
int hash = calc_hash(strBuf, strBuf.length);
ma = hashSpace[hash];
while (true) {
if ((strBuf.length != ma.station.length) || (Arrays.compare(strBuf, ma.station) != 0)) { // hash collision
ma = ma.next;
continue;
}
else { // hit
double min = Math.round(Double.valueOf(ma.min)) / 10.0;
double avg = Math.round(Double.valueOf(ma.sum) / Double.valueOf(ma.count)) / 10.0;
double max = Math.round(Double.valueOf(ma.max)) / 10.0;
out += staArr[i] + "=" + min + "/" + avg + "/" + max;
if (i != (numStations - 1)) {
out += ", ";
}
break;
}
}
}
out += "}\n";
System.out.print(out);
mraf.getChannel().close();
mraf.close();
}
catch (IOException ex) {
System.exit(1);
}
System.exit(0);
}
}
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