shubhamvishu commented on code in PR #16631:
URL: https://github.com/apache/lucene/pull/16631#discussion_r3961527388
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lucene/core/src/java25/org/apache/lucene/internal/vectorization/PanamaVectorUtilSupport.java:
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@@ -584,6 +588,24 @@ private static int int4DotProductBody(ByteVectorLoader a,
ByteVectorLoader b, in
return sum;
}
+ @Override
+ public void int4Unpack(byte[] packed, byte[] unpacked) {
+ final int len = packed.length;
+ final int bound = BYTE_SPECIES_FULL.loopBound(len);
+ int i = 0;
+ for (; i < bound; i += BYTE_SPECIES_FULL.length()) {
+ ByteVector v = ByteVector.fromArray(BYTE_SPECIES_FULL, packed, i);
+ // LSHR is a logical shift within the byte lane, so the high nibble
needs no mask.
+ v.lanewise(LSHR, 4).intoArray(unpacked, i);
+ v.lanewise(VectorOperators.AND, (byte) 0x0F).intoArray(unpacked, len +
i);
+ }
+ // scalar tail
+ for (; i < len; i++) {
+ unpacked[i] = (byte) ((packed[i] >> 4) & 0x0F);
+ unpacked[len + i] = (byte) (packed[i] & 0x0F);
+ }
Review Comment:
Minor : I understand this has been an convention in this file though I think
we could "possibly" further optimize for the case where vector length isn't
divisible by `BYTE_SPECIES_FULL.length` (eg : 300 dim and
`BYTE_SPECIES_FULL.length` as 32 like Graviton 3) and the remaining tail is >
16 or > 8; provided simd over that smaller tail/chunk is faster than simple
iteration over it.
At the same time, how often are there such non power of 2 dimensions used in
real scenario? maybe not often?
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