jasonk000 commented on a change in pull request #11721:
URL: https://github.com/apache/kafka/pull/11721#discussion_r799082813
##########
File path: clients/src/main/java/org/apache/kafka/common/utils/ByteUtils.java
##########
@@ -386,18 +386,39 @@ public static void writeDouble(double value, ByteBuffer
buffer) {
buffer.putDouble(value);
}
+ final static int[] LEADING_ZEROS_TO_U_VARINT_SIZE = new int[] {
+ // 32 bits, and each 7-bits adds one byte to the output
+ 5, 5, 5, 5, // 32
+ 4, 4, 4, 4, 4, 4, 4, // 28
+ 3, 3, 3, 3, 3, 3, 3, // 21
+ 2, 2, 2, 2, 2, 2, 2, // 14
+ 1, 1, 1, 1, 1, 1, 1, // 7
+ 1 // 0
+ };
+
+ final static int[] LEADING_ZEROS_TO_U_VARLONG_SIZE = new int[] {
+ // 64 bits, and each 7-bits adds one byte to the output
+ 10, // 64
+ 9, 9, 9, 9, 9, 9, 9, // 63
+ 8, 8, 8, 8, 8, 8, 8, // 56
+ 7, 7, 7, 7, 7, 7, 7, // 49
+ 6, 6, 6, 6, 6, 6, 6, // 42
+ 5, 5, 5, 5, 5, 5, 5, // 35
+ 4, 4, 4, 4, 4, 4, 4, // 28
+ 3, 3, 3, 3, 3, 3, 3, // 21
+ 2, 2, 2, 2, 2, 2, 2, // 14
+ 1, 1, 1, 1, 1, 1, 1, // 7
+ 1 // 0
+ };
+
/**
* Number of bytes needed to encode an integer in unsigned variable-length
format.
*
* @param value The signed value
*/
public static int sizeOfUnsignedVarint(int value) {
- int bytes = 1;
- while ((value & 0xffffff80) != 0L) {
- bytes += 1;
- value >>>= 7;
- }
- return bytes;
+ int leadingZeros = Integer.numberOfLeadingZeros(value);
+ return LEADING_ZEROS_TO_U_VARINT_SIZE[leadingZeros];
Review comment:
OK, got it. Thank you for the nudges. They are now effectively identical
in performance, and the math-version uses 1 less cmp/mov (for array bounds &
fetch), with one extra instruction, and no requirement to hit the cache.
```
Benchmark
Mode Cnt Score Error Units
ByteUtilsBenchmark.testSizeOfUnsignedVarint
thrpt 20 503633.665 ± 5214.083 ops/ms
ByteUtilsBenchmark.testSizeOfUnsignedVarint:IPC
thrpt 2 4.608 insns/clk
ByteUtilsBenchmark.testSizeOfUnsignedVarint:L1-dcache-loads
thrpt 2 13.002 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarint:branches
thrpt 2 5.005 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarint:instructions
thrpt 2 31.080 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarintMath
thrpt 20 507438.241 ± 5268.695 ops/ms
ByteUtilsBenchmark.testSizeOfUnsignedVarintMath:IPC
thrpt 2 4.789 insns/clk
ByteUtilsBenchmark.testSizeOfUnsignedVarintMath:L1-dcache-loads
thrpt 2 11.992 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarintMath:branches
thrpt 2 4.004 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarintMath:instructions
thrpt 2 32.059 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarintOriginal
thrpt 20 371946.626 ± 3105.947 ops/ms
ByteUtilsBenchmark.testSizeOfUnsignedVarintOriginal:IPC
thrpt 2 5.360 insns/clk
ByteUtilsBenchmark.testSizeOfUnsignedVarintOriginal:L1-dcache-loads
thrpt 2 14.002 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarintOriginal:branches
thrpt 2 7.992 #/op
ByteUtilsBenchmark.testSizeOfUnsignedVarintOriginal:instructions
thrpt 2 48.931 #/op
```
I'll switch the code over.
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