diff options
Diffstat (limited to 'sysdeps/aarch64/strlen.S')
| -rw-r--r-- | sysdeps/aarch64/strlen.S | 25 |
1 files changed, 9 insertions, 16 deletions
diff --git a/sysdeps/aarch64/strlen.S b/sysdeps/aarch64/strlen.S index a2310871c2..3a5d088407 100644 --- a/sysdeps/aarch64/strlen.S +++ b/sysdeps/aarch64/strlen.S @@ -34,35 +34,29 @@ #define src x1 #define synd x2 #define tmp x3 -#define wtmp w3 #define shift x4 #define data q0 #define vdata v0 #define vhas_nul v1 -#define vrepmask v2 -#define vend v3 -#define dend d3 +#define vend v2 +#define dend d2 /* Core algorithm: - For each 16-byte chunk we calculate a 64-bit syndrome value with four bits - per byte. For even bytes, bits 0-3 are set if the relevant byte matched the - requested character or the byte is NUL. Bits 4-7 must be zero. Bits 4-7 are - set likewise for odd bytes so that adjacent bytes can be merged. Since the - bits in the syndrome reflect the order in which things occur in the original - string, counting trailing zeros identifies exactly which byte matched. */ + 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. */ ENTRY (STRLEN) PTR_ARG (0) bic src, srcin, 15 - mov wtmp, 0xf00f ld1 {vdata.16b}, [src] - dup vrepmask.8h, wtmp cmeq vhas_nul.16b, vdata.16b, 0 lsl shift, srcin, 2 - and vhas_nul.16b, vhas_nul.16b, vrepmask.16b - addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */ + shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */ fmov synd, dend lsr synd, synd, shift cbz synd, L(loop) @@ -80,8 +74,7 @@ L(loop): fmov synd, dend cbz synd, L(loop) - and vhas_nul.16b, vhas_nul.16b, vrepmask.16b - addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */ + shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */ sub result, src, srcin fmov synd, dend #ifndef __AARCH64EB__ |