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internal/bytealg: unroll compare_arm64.s chunk16_loop to 32 bytes/iter #79728

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internal/bytealg: unroll compare_arm64.s chunk16_loop to 32 bytes/iter #79728

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31 changes: 25 additions & 6 deletions src/internal/bytealg/compare_arm64.s
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Original file line number Diff line number Diff line change
Expand Up @@ -39,19 +39,38 @@ TEXT cmpbody<>(SB),NOSPLIT|NOFRAME,$0-0
CSEL LT, R3, R1, R6 // R6 is min(R1, R3)

CBZ R6, samebytes
BIC $0xf, R6, R10
CBZ R10, small // length < 16
ADD R0, R10 // end of chunk16
// length >= 16
chunk16_loop:
BIC $0x1f, R6, R10
CBZ R10, chunk16 // length < 32, try single chunk16
ADD R0, R10 // end of chunk32
// length >= 32
chunk32_loop:
LDP.P 16(R0), (R4, R8)
LDP.P 16(R2), (R5, R9)
CMP R4, R5
BNE cmp
CMP R8, R9
BNE cmpnext
LDP.P 16(R0), (R4, R8)
LDP.P 16(R2), (R5, R9)
CMP R4, R5
BNE cmp
CMP R8, R9
BNE cmpnext
CMP R10, R0
BNE chunk16_loop
BNE chunk32_loop
AND $0x1f, R6, R6 // remaining 0-31 bytes
CBZ R6, samebytes
// handle remaining 0-31 bytes: one possible 16-byte chunk then tail
TBZ $4, R6, small_direct
chunk16:
TBZ $4, R6, small // length < 16
LDP.P 16(R0), (R4, R8)
LDP.P 16(R2), (R5, R9)
CMP R4, R5
BNE cmp
CMP R8, R9
BNE cmpnext
small_direct:
AND $0xf, R6, R6
CBZ R6, samebytes
SUBS $8, R6
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