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| author | Wilco Dijkstra <wilco.dijkstra@arm.com> | 2023-01-11 13:53:05 +0000 |
|---|---|---|
| committer | Wilco Dijkstra <wilco.dijkstra@arm.com> | 2023-01-17 15:09:18 +0000 |
| commit | ad098893ba3c3344a5f2f6ab1627c47204afdb47 (patch) | |
| tree | 91d9ebc4e4ca1b8624eb93bd60e63236bb73c4c1 /sysdeps/aarch64 | |
| parent | 03c8ce5000198947a4dd7b2c14e5131738fda62b (diff) | |
| download | glibc-ad098893ba3c3344a5f2f6ab1627c47204afdb47.tar.gz glibc-ad098893ba3c3344a5f2f6ab1627c47204afdb47.tar.xz glibc-ad098893ba3c3344a5f2f6ab1627c47204afdb47.zip | |
AArch64: Optimize strnlen
Optimize strnlen using the shrn instruction and improve the main loop. Small strings are around 10% faster, large strings are 40% faster on modern CPUs. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Diffstat (limited to 'sysdeps/aarch64')
| -rw-r--r-- | sysdeps/aarch64/strnlen.S | 39 |
1 files changed, 18 insertions, 21 deletions
diff --git a/sysdeps/aarch64/strnlen.S b/sysdeps/aarch64/strnlen.S index 35fd14804d..21112fbf76 100644 --- a/sysdeps/aarch64/strnlen.S +++ b/sysdeps/aarch64/strnlen.S @@ -44,19 +44,16 @@ /* Core algorithm: - - For each 16-byte chunk we calculate a 64-bit nibble mask value with four bits - per byte. We take 4 bits of every comparison byte with shift right and narrow - by 4 instruction. Since the bits in the nibble mask reflect the order in - which things occur in the original string, counting trailing zeros identifies - exactly which byte matched. */ + Process the string in 16-byte aligned chunks. Compute a 64-bit mask with + four bits per byte using the shrn instruction. A count trailing zeros then + identifies the first zero byte. */ ENTRY (__strnlen) PTR_ARG (0) SIZE_ARG (1) bic src, srcin, 15 cbz cntin, L(nomatch) - ld1 {vdata.16b}, [src], 16 + ld1 {vdata.16b}, [src] cmeq vhas_chr.16b, vdata.16b, 0 lsl shift, srcin, 2 shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */ @@ -71,36 +68,40 @@ L(finish): csel result, cntin, result, ls ret +L(nomatch): + mov result, cntin + ret + L(start_loop): sub tmp, src, srcin + add tmp, tmp, 17 subs cntrem, cntin, tmp - b.ls L(nomatch) + b.lo L(nomatch) /* Make sure that it won't overread by a 16-byte chunk */ - add tmp, cntrem, 15 - tbnz tmp, 4, L(loop32_2) - + tbz cntrem, 4, L(loop32_2) + sub src, src, 16 .p2align 5 L(loop32): - ldr qdata, [src], 16 + ldr qdata, [src, 32]! cmeq vhas_chr.16b, vdata.16b, 0 umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */ fmov synd, dend cbnz synd, L(end) L(loop32_2): - ldr qdata, [src], 16 + ldr qdata, [src, 16] subs cntrem, cntrem, 32 cmeq vhas_chr.16b, vdata.16b, 0 - b.ls L(end) + b.lo L(end_2) umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */ fmov synd, dend cbz synd, L(loop32) - +L(end_2): + add src, src, 16 L(end): shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */ - sub src, src, 16 - mov synd, vend.d[0] sub result, src, srcin + fmov synd, dend #ifndef __AARCH64EB__ rbit synd, synd #endif @@ -110,10 +111,6 @@ L(end): csel result, cntin, result, ls ret -L(nomatch): - mov result, cntin - ret - END (__strnlen) libc_hidden_def (__strnlen) weak_alias (__strnlen, strnlen) |