SVE Instruction List by Dougall Johnson
CLASTA (vectors): Conditionally extract element after last to vector register
CLASTA Zdn.D, Pg, Zdn.D, Zm.D (SVE (SME
svfloat64_t svclasta[_f64](svbool_t pg, svfloat64_t fallback, svfloat64_t data)
svint64_t svclasta[_s64](svbool_t pg, svint64_t fallback, svint64_t data)
svuint64_t svclasta[_u64](svbool_t pg, svuint64_t fallback, svuint64_t data)
128-bit SVE
Find the last (leftmost) 64-bit element from (2) where the corresponding predicate bit in (1) is non-zero, then broadcast the next element to all 64-bit lanes of (4). If the last corresponding predicate bit is non-zero, broadcast the first (rightmost) element from (1) to all lanes of (4). If all corresponding predicate bits are zero, preserve the value from (3).
256-bit SVE
Find the last (leftmost) 64-bit element from (2) where the corresponding predicate bit in (1) is non-zero, then broadcast the next element to all 64-bit lanes of (4). If the last corresponding predicate bit is non-zero, broadcast the first (rightmost) element from (1) to all lanes of (4). If all corresponding predicate bits are zero, preserve the value from (3).
512-bit SVE
Find the last (leftmost) 64-bit element from (2) where the corresponding predicate bit in (1) is non-zero, then broadcast the next element to all 64-bit lanes of (4). If the last corresponding predicate bit is non-zero, broadcast the first (rightmost) element from (1) to all lanes of (4). If all corresponding predicate bits are zero, preserve the value from (3).
Larger sizes
1024-bit SVE
Find the last (leftmost) 64-bit element from (2) where the corresponding predicate bit in (1) is non-zero, then broadcast the next element to all 64-bit lanes of (4). If the last corresponding predicate bit is non-zero, broadcast the first (rightmost) element from (1) to all lanes of (4). If all corresponding predicate bits are zero, preserve the value from (3).
2048-bit SVE
Find the last (leftmost) 64-bit element from (2) where the corresponding predicate bit in (1) is non-zero, then broadcast the next element to all 64-bit lanes of (4). If the last corresponding predicate bit is non-zero, broadcast the first (rightmost) element from (1) to all lanes of (4). If all corresponding predicate bits are zero, preserve the value from (3).
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Inspired by and based on the x86/x64 SIMD Instruction List by Daytime.