diff options
Diffstat (limited to 'sysdeps/aarch64')
| -rw-r--r-- | sysdeps/aarch64/strchr.S | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/sysdeps/aarch64/strchr.S b/sysdeps/aarch64/strchr.S new file mode 100644 index 0000000000..a89725d96f --- /dev/null +++ b/sysdeps/aarch64/strchr.S @@ -0,0 +1,138 @@ +/* strchr - find a character in a string + + Copyright (C) 2014 Free Software Foundation, Inc. + + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library. If not, see + <http://www.gnu.org/licenses/>. */ + +#include <sysdep.h> + +/* Assumptions: + * + * ARMv8-a, AArch64 + */ + +/* Arguments and results. */ +#define srcin x0 +#define chrin w1 + +#define result x0 + +#define src x2 +#define tmp1 x3 +#define wtmp2 w4 +#define tmp3 x5 + +#define vrepchr v0 +#define vdata1 v1 +#define vdata2 v2 +#define vhas_nul1 v3 +#define vhas_nul2 v4 +#define vhas_chr1 v5 +#define vhas_chr2 v6 +#define vrepmask_0 v7 +#define vrepmask_c v16 +#define vend1 v17 +#define vend2 v18 + + /* Core algorithm. + For each 32-byte hunk we calculate a 64-bit syndrome value, with + two bits per byte (LSB is always in bits 0 and 1, for both big + and little-endian systems). Bit 0 is set iff the relevant byte + matched the requested character. Bit 1 is set iff the + relevant byte matched the NUL end of string (we trigger off bit0 + for the special case of looking for NUL). Since the bits + in the syndrome reflect exactly the order in which things occur + in the original string a count_trailing_zeros() operation will + identify exactly which byte is causing the termination, and why. */ + +/* Locals and temporaries. */ + +ENTRY (strchr) + mov wtmp2, #0x0401 + movk wtmp2, #0x4010, lsl #16 + dup vrepchr.16b, chrin + bic src, srcin, #31 + dup vrepmask_c.4s, wtmp2 + ands tmp1, srcin, #31 + add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s // lsl #1 + b.eq L(loop) + + /* Input string is not 32-byte aligned. Rather than forcing + the padding bytes to a safe value, we calculate the syndrome + for all the bytes, but then mask off those bits of the + syndrome that are related to the padding. */ + ld1 {vdata1.16b, vdata2.16b}, [src], #32 + neg tmp1, tmp1 + cmeq vhas_nul1.16b, vdata1.16b, #0 + cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b + cmeq vhas_nul2.16b, vdata2.16b, #0 + cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b + and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b + and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b + and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b + and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b + orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b + orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b + lsl tmp1, tmp1, #1 + addp vend1.16b, vend1.16b, vend2.16b // 256->128 + mov tmp3, #~0 + addp vend1.16b, vend1.16b, vend2.16b // 128->64 + lsr tmp1, tmp3, tmp1 + + mov tmp3, vend1.2d[0] + bic tmp1, tmp3, tmp1 // Mask padding bits. + cbnz tmp1, L(tail) + +L(loop): + ld1 {vdata1.16b, vdata2.16b}, [src], #32 + cmeq vhas_nul1.16b, vdata1.16b, #0 + cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b + cmeq vhas_nul2.16b, vdata2.16b, #0 + cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b + /* Use a fast check for the termination condition. */ + orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b + orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b + orr vend1.16b, vend1.16b, vend2.16b + addp vend1.2d, vend1.2d, vend1.2d + mov tmp1, vend1.2d[0] + cbz tmp1, L(loop) + + /* Termination condition found. Now need to establish exactly why + we terminated. */ + and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b + and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b + and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b + and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b + orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b + orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b + addp vend1.16b, vend1.16b, vend2.16b // 256->128 + addp vend1.16b, vend1.16b, vend2.16b // 128->64 + + mov tmp1, vend1.2d[0] +L(tail): + sub src, src, #32 + rbit tmp1, tmp1 + clz tmp1, tmp1 + /* Tmp1 is even if the target charager was found first. Otherwise + we've found the end of string and we weren't looking for NUL. */ + tst tmp1, #1 + add result, src, tmp1, lsr #1 + csel result, result, xzr, eq + ret +END (strchr) +libc_hidden_builtin_def (strchr) +weak_alias (strchr, index) |