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SVE_MATCH FIX - add fallback path if nkeys > VL #3345

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Merged
jasonrandrews merged 1 commit into from
Jun 2, 2026
+6 −0
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SVE_MATCH FIX - add fallback path if nkeys > VL #3345

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6 changes: 6 additions & 0 deletions content/learning-paths/servers-and-cloud-computing/sve2-match/sve2-match-search.md
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,7 @@ int search_sve2_match_u8(const uint8_t *hay, size_t n, const uint8_t *keys,
size_t nkeys) {
if (nkeys == 0) return 0;
const size_t VL = svcntb();
if (nkeys > VL) return search_generic_u8(hay, n, keys, nkeys);
svbool_t pg = svptrue_b8();
uint8_t tmp[256];
for (size_t i = 0; i < VL; ++i) tmp[i] = keys[i % nkeys];
Expand All @@ -121,6 +122,7 @@ int search_sve2_match_u16(const uint16_t *hay, size_t n, const uint16_t *keys,
size_t nkeys) {
if (nkeys == 0) return 0;
const size_t VL = svcnth();
if (nkeys > VL) return search_generic_u16(hay, n, keys, nkeys);
svbool_t pg = svptrue_b16();
uint16_t tmp[128];
for (size_t i = 0; i < VL; ++i) tmp[i] = keys[i % nkeys];
Expand All @@ -142,6 +144,7 @@ int search_sve2_match_u16(const uint16_t *hay, size_t n, const uint16_t *keys,
The SVE MATCH implementation with the `search_sve2_match_u8()` and `search_sve2_match_u16()` functions provide an efficient vectorized search approach with these key technical aspects:
- Uses SVE2's specialized MATCH instruction to compare multiple elements against multiple keys in parallel
- Leverages hardware-specific vector length through `svcntb()` for scalability
- In the case where the number of keys, `nkeys`, exceeds the hardware-specific vector length, the implementation falls back to the generic scalar version.
- Prepares a vector of search keys that's compared against blocks of data
- Processes data in vector-sized chunks with early termination when matches are found. Stops immediately when any element in the vector matches.
- Falls back to scalar code for remainder elements
Expand All @@ -157,6 +160,8 @@ int search_sve2_match_u8_unrolled(const uint8_t *hay, size_t n, const uint8_t *k
size_t nkeys) {
if (nkeys == 0) return 0;
const size_t VL = svcntb();
if (nkeys > VL) return search_generic_u8(hay, n, keys, nkeys);

svbool_t pg = svptrue_b8();

// Prepare key vector
Expand Down Expand Up @@ -205,6 +210,7 @@ int search_sve2_match_u16_unrolled(const uint16_t *hay, size_t n, const uint16_t
size_t nkeys) {
if (nkeys == 0) return 0;
const size_t VL = svcnth();
if (nkeys > VL) return search_generic_u16(hay, n, keys, nkeys);
svbool_t pg = svptrue_b16();

// Prepare key vector
Expand Down
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