org.opentripplanner.common.geometry.DlugoszVarLenIntPacker Maven / Gradle / Ivy
package org.opentripplanner.common.geometry;
import java.io.ByteArrayOutputStream;
import java.util.ArrayList;
import java.util.List;
/**
* Variable-length integer encoding. This optimize integer storage when most of the values are
* small, but few of them can be quite large (as in a geometry). Adapted Dlugosz scheme to support
* signed int whose average are around 0.
*
* See Dlugosz' variable-length integer encoding (http://www.dlugosz.com/ZIP2/VLI.html).
*
* @author laurent
*
*/
public class DlugoszVarLenIntPacker {
public static byte[] pack(int[] arr) {
if (arr == null) {
return null;
}
ByteArrayOutputStream baos = new ByteArrayOutputStream(arr.length);
for (int i : arr) {
if (i >= -64 && i <= 63) {
// 0xxx xxxx -> 7 bits value
// i+64 between 0 and 127, 7 bits
int ui = i + 64;
baos.write(ui);
} else if (i >= -8192 && i <= 8191) {
// 10xx xxxx + 8 -> 14 bits value
// i+8192 between 0 and 16383
int ui = i + 8192;
baos.write(0x80 | (ui >> 8)); // 6b MSB
baos.write(ui & 0xFF); // 8b LSB
} else if (i >= -1048576 && i <= 1048575) {
// 110 xxxx + 2x8 -> 21 bits value
// i + 1048576 between 0 and 2097151
int ui = i + 1048576;
baos.write(0xC0 | (ui >> 16)); // 5b MSB
baos.write((ui >> 8) & 0xFF); // 8b
baos.write(ui & 0xFF); // 8b
} else if (i >= -67108864 && i <= 67108863) {
// 1110 0xxx + 3x8 -> 27 bits value
// i + 67108864 between 0 and 134217727
int ui = i + 67108864;
baos.write(0xE0 | (ui >> 24)); // 3b MSB
baos.write((ui >> 16) & 0xFF); // 8b
baos.write((ui >> 8) & 0xFF); // 8b
baos.write(ui & 0xFF); // 8b
} else { // int can't have more than 32 bits
// 1110 1xxx + 4x8 -> 35 bits value
// i + 0x80000000 fits in 35 bits for sure
long ui = (long) i + 2147483648L;
baos.write((int) (0xE8 | (ui >> 32))); // 3b MSB
baos.write((int) ((ui >> 24) & 0xFF)); // 8b
baos.write((int) ((ui >> 16) & 0xFF)); // 8b
baos.write((int) ((ui >> 8) & 0xFF)); // 8b
baos.write((int) (ui & 0xFF)); // 8b
}
}
return baos.toByteArray();
}
public static int[] unpack(byte[] arr) {
if (arr == null) {
return null;
}
List retval = new ArrayList(arr.length);
int i = 0;
while (i < arr.length) {
int v1 = arr[i] & 0xFF;
i++;
if ((v1 & 0x80) == 0x00) {
// 0xxx xxxx -> 7 bits value
int sv = (v1 & 0x7F) - 64;
retval.add(sv);
} else if ((v1 & 0xC0) == 0x80) {
// 10xx xxxx + 8 -> 14 bits value
int sv = ((v1 & 0x3F) << 8) + (arr[i] & 0xFF) - 8192;
i++;
retval.add(sv);
} else if ((v1 & 0xE0) == 0xC0) {
// 110 xxxx + 2x8 -> 21 bits value
int sv = ((v1 & 0x1F) << 16) + ((arr[i] & 0xFF) << 8) + (arr[i + 1] & 0xFF)
- 1048576;
i += 2;
retval.add(sv);
} else if ((v1 & 0xF8) == 0xE0) {
// 1110 0xxx + 3x8 -> 27 bits value
int sv = ((v1 & 0x1F) << 24) + ((arr[i] & 0xFF) << 16) + ((arr[i + 1] & 0xFF) << 8)
+ (arr[i + 2] & 0xFF) - 67108864;
i += 3;
retval.add(sv);
} else {
// 1110 1xxx + 4x8 -> 35 bits value
long sv = (((long) v1 & 0x1F) << 32) + ((arr[i] & 0xFF) << 24)
+ ((arr[i + 1] & 0xFF) << 16) + ((arr[i + 2] & 0xFF) << 8)
+ (arr[i + 3] & 0xFF) - 2147483648L;
i += 4;
retval.add((int) sv);
}
}
int[] bufret = new int[retval.size()];
i = 0;
for (int v : retval) {
bufret[i++] = v;
}
return bufret;
}
}