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8311207: Cleanup for Optimization for UUID.toString #14745

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8311207: Cleanup for Optimization for UUID.toString #14745

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468bc61
8311207: Optimization for j.u.UUID.toString
wenshao Jul 1, 2023
244c0eb
use big endian
wenshao Jul 1, 2023
b6c59e0
Suggested HexDigits change
liach Jul 1, 2023
425559f
Merge pull request #1 from liachmodded/optimization_for_uuid_to_string
wenshao Jul 1, 2023
76dba96
revert to the previous version
wenshao Jul 1, 2023
43ec99d
private static final Unsafe
wenshao Jul 1, 2023
6abf314
Explain the rationale
liach Jul 1, 2023
e5274dd
code style
wenshao Jul 1, 2023
d6bb272
fix typo
wenshao Jul 8, 2023
25cf014
use ByteArrayLittleEndian
wenshao Sep 5, 2023
6996243
Merge branch 'master' into optimization_for_uuid_to_string
wenshao Sep 5, 2023
141880f
fix java doc, big-endian -> little-endian
wenshao Sep 5, 2023
3f6d35d
remove redundant parentheses
wenshao Sep 5, 2023
2d36332
Merge branch 'master' into optimization_for_uuid_to_string
wenshao Sep 5, 2023
747e813
reversed how & hi
wenshao Sep 7, 2023
384354d
add DIGITS description
wenshao Sep 8, 2023
46b4b05
lo | hi => hi | lo
wenshao Sep 8, 2023
10b1e6e
Merge branch 'master' into optimization_for_uuid_to_string
wenshao Sep 12, 2023
4f6ed3e
merge from master
wenshao Sep 12, 2023
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26 changes: 13 additions & 13 deletions src/java.base/share/classes/java/util/UUID.java
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@

import jdk.internal.access.JavaLangAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.util.ByteArray;
import jdk.internal.util.ByteArrayLittleEndian;
import jdk.internal.util.HexDigits;

/**
Expand Down Expand Up @@ -470,34 +470,34 @@ public String toString() {
long lsb = leastSigBits;
long msb = mostSigBits;
byte[] buf = new byte[36];
ByteArray.setLong(
ByteArrayLittleEndian.setLong(
buf,
0,
HexDigits.digit((int) (msb >> 56), (int) (msb >> 48), (int) (msb >> 40), (int) (msb >> 32)));
HexDigits.packDigits((int) (msb >> 56), (int) (msb >> 48), (int) (msb >> 40), (int) (msb >> 32)));
buf[8] = '-';
ByteArray.setInt(
ByteArrayLittleEndian.setInt(
buf,
9,
HexDigits.digit(((int) msb) >> 24, ((int) msb) >> 16));
HexDigits.packDigits(((int) msb) >> 24, ((int) msb) >> 16));
buf[13] = '-';
ByteArray.setInt(
ByteArrayLittleEndian.setInt(
buf,
14,
HexDigits.digit(((int) msb) >> 8, (int) msb));
HexDigits.packDigits(((int) msb) >> 8, (int) msb));
buf[18] = '-';
ByteArray.setInt(
ByteArrayLittleEndian.setInt(
buf,
19,
HexDigits.digit((int) (lsb >> 56), (int) (lsb >> 48)));
HexDigits.packDigits((int) (lsb >> 56), (int) (lsb >> 48)));
buf[23] = '-';
ByteArray.setLong(
ByteArrayLittleEndian.setLong(
buf,
24,
HexDigits.digit(((int) (lsb >> 40)), (int) (lsb >> 32), ((int) lsb) >> 24, ((int) lsb) >> 16));
ByteArray.setInt(
HexDigits.packDigits((int) (lsb >> 40), (int) (lsb >> 32), ((int) lsb) >> 24, ((int) lsb) >> 16));
ByteArrayLittleEndian.setInt(
buf,
32,
HexDigits.digit(((int) lsb) >> 8, (int) lsb));
HexDigits.packDigits(((int) lsb) >> 8, (int) lsb));

try {
return jla.newStringNoRepl(buf, StandardCharsets.ISO_8859_1);
Expand Down
67 changes: 30 additions & 37 deletions src/java.base/share/classes/jdk/internal/util/HexDigits.java
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Original file line number Diff line number Diff line change
Expand Up @@ -39,38 +39,27 @@ public final class HexDigits implements Digits {
* Each element of the array represents the ascii encoded
* hex relative to its index, for example:<p>
* <pre>
* 0 -> '00' -> ('0' << 8) | '0' -> 12336
* 1 -> '01' -> ('0' << 8) | '1' -> 12337
* 2 -> '02' -> ('0' << 8) | '2' -> 12338
* 0 -> '00' -> '0' | ('0' << 8) -> 0x3030
* 1 -> '01' -> '0' | ('1' << 8) -> 0x3130
* 2 -> '02' -> '0' | ('2' << 8) -> 0x3230
*
* ...
*
* 10 -> '0a' -> ('0' << 8) | 'a' -> 12385
* 11 -> '0b' -> ('0' << 8) | 'b' -> 12386
* 12 -> '0c' -> ('0' << 8) | 'b' -> 12387
* 10 -> '0a' -> '0' | ('a' << 8) -> 0x6130
* 11 -> '0b' -> '0' | ('b' << 8) -> 0x6230
* 12 -> '0c' -> '0' | ('b' << 8) -> 0x6330
*
* ...
*
* 26 -> '1a' -> ('1' << 8) | 'a' -> 12641
* 27 -> '1b' -> ('1' << 8) | 'b' -> 12642
* 28 -> '1c' -> ('1' << 8) | 'c' -> 12643
* 26 -> '1a' -> '1' | ('a' << 8) -> 0x6131
* 27 -> '1b' -> '1' | ('b' << 8) -> 0x6231
* 28 -> '1c' -> '1' | ('c' << 8) -> 0x6331
*
* ...
*
* 253 -> 'fd' -> ('f' << 8) | 'd' -> 26212
* 254 -> 'fe' -> ('f' << 8) | 'e' -> 26213
* 255 -> 'ff' -> ('f' << 8) | 'f' -> 26214
* </pre>
* <p>use like this:
* <pre>
* int v = 254;
*
* char[] chars = new char[2];
*
* short i = DIGITS[v]; // 26213
*
* chars[0] = (char) (byte) (i >> 8); // 'f'
* chars[1] = (char) (byte) i; // 'e'
* 253 -> 'fd' -> 'f' | ('d' << 8) -> 0x6466
* 254 -> 'fe' -> 'f' | ('e' << 8) -> 0x6566
* 255 -> 'ff' -> 'f' | ('f' << 8) -> 0x6666
* </pre>
*/
@Stable
Expand All @@ -85,10 +74,10 @@ public final class HexDigits implements Digits {
short[] digits = new short[16 * 16];

for (int i = 0; i < 16; i++) {
short hi = (short) ((i < 10 ? i + '0' : i - 10 + 'a') << 8);
short lo = (short) (i < 10 ? i + '0' : i - 10 + 'a');

for (int j = 0; j < 16; j++) {
short lo = (short) (j < 10 ? j + '0' : j - 10 + 'a');
short hi = (short) ((j < 10 ? j + '0' : j - 10 + 'a') << 8);
digits[(i << 4) + j] = (short) (hi | lo);
}
}
Expand All @@ -103,20 +92,24 @@ private HexDigits() {
}

/**
* Combine two hex shorts into one int based on big endian
* Return a little-endian packed integer for the 4 ASCII bytes for an input unsigned 2-byte integer.
* {@code b0} is the most significant byte and {@code b1} is the least significant byte.
* The integer is passed byte-wise to allow reordering of execution.
*/
public static int digit(int b0, int b1) {
return (DIGITS[b0 & 0xff] << 16) | DIGITS[b1 & 0xff];
public static int packDigits(int b0, int b1) {
return DIGITS[b0 & 0xff] | (DIGITS[b1 & 0xff] << 16);
}

/**
* Combine four hex shorts into one long based on big endian
* Return a little-endian packed long for the 8 ASCII bytes for an input unsigned 4-byte integer.
* {@code b0} is the most significant byte and {@code b3} is the least significant byte.
* The integer is passed byte-wise to allow reordering of execution.
*/
public static long digit(int b0, int b1, int b2, int b3) {
return (((long) DIGITS[b0 & 0xff]) << 48)
| (((long) DIGITS[b1 & 0xff]) << 32)
| (DIGITS[b2 & 0xff] << 16)
| DIGITS[b3 & 0xff];
public static long packDigits(int b0, int b1, int b2, int b3) {
return DIGITS[b0 & 0xff]
| (DIGITS[b1 & 0xff] << 16)
| (((long) DIGITS[b2 & 0xff]) << 32)
| (((long) DIGITS[b3 & 0xff]) << 48);
Comment on lines +109 to +112
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@RogerRiggs RogerRiggs Sep 12, 2023

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Can you reverse the order of these source lines to put the shifts of the higher order bits before the lower order bit shifts. 3333222211110000. Its easier to understand where the bits end up in the long.
The rest of the change is better focused.

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@wenshao wenshao Sep 12, 2023 •
edited
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if reverse packDigits order, performance will be slow, I don't know why yet.

The following is the data running on MacBookPro M1 Max :

make test TEST="micro:java.util.UUIDBench.toString"

Benchmark           (size)   Mode  Cnt   Score   Error   Units (current order 4f6ed3e6)
UUIDBench.toString   20000  thrpt   15  96.396 ? 0.946  ops/us


Benchmark           (size)   Mode  Cnt   Score   Error   Units (reverse packDigits order)
UUIDBench.toString   20000  thrpt   15  86.496 ? 0.542  ops/us

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@cl4es cl4es Sep 12, 2023

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Looks like something that might be an interesting puzzler for JIT compiler folks. Perhaps added implicit casts to long messes something up?

}

@Override
Expand All @@ -125,15 +118,15 @@ public int digits(long value, byte[] buffer, int index,
while ((value & ~0xFF) != 0) {
int digits = DIGITS[(int) (value & 0xFF)];
value >>>= 8;
putCharMH.invokeExact(buffer, --index, digits & 0xFF);
putCharMH.invokeExact(buffer, --index, digits >> 8);
putCharMH.invokeExact(buffer, --index, digits & 0xFF);
}

int digits = DIGITS[(int) (value & 0xFF)];
putCharMH.invokeExact(buffer, --index, digits & 0xFF);
putCharMH.invokeExact(buffer, --index, digits >> 8);

if (0xF < value) {
putCharMH.invokeExact(buffer, --index, digits >> 8);
putCharMH.invokeExact(buffer, --index, digits & 0xFF);
}

return index;
Expand Down