diff options
Diffstat (limited to 'libc/ports/sysdeps/aarch64/memcmp.S')
| -rw-r--r-- | libc/ports/sysdeps/aarch64/memcmp.S | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/libc/ports/sysdeps/aarch64/memcmp.S b/libc/ports/sysdeps/aarch64/memcmp.S new file mode 100644 index 000000000..6398ddd3e --- /dev/null +++ b/libc/ports/sysdeps/aarch64/memcmp.S @@ -0,0 +1,151 @@ +/* memcmp - compare memory + + Copyright (C) 2013 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 + */ + +/* Parameters and result. */ +#define src1 x0 +#define src2 x1 +#define limit x2 +#define result x0 + +/* Internal variables. */ +#define data1 x3 +#define data1w w3 +#define data2 x4 +#define data2w w4 +#define has_nul x5 +#define diff x6 +#define endloop x7 +#define tmp1 x8 +#define tmp2 x9 +#define tmp3 x10 +#define pos x11 +#define limit_wd x12 +#define mask x13 + +ENTRY_ALIGN (memcmp, 6) + cbz limit, L(ret0) + eor tmp1, src1, src2 + tst tmp1, #7 + b.ne L(misaligned8) + ands tmp1, src1, #7 + b.ne L(mutual_align) + add limit_wd, limit, #7 + lsr limit_wd, limit_wd, #3 + /* Start of performance-critical section -- one 64B cache line. */ +L(loop_aligned): + ldr data1, [src1], #8 + ldr data2, [src2], #8 +L(start_realigned): + subs limit_wd, limit_wd, #1 + eor diff, data1, data2 /* Non-zero if differences found. */ + csinv endloop, diff, xzr, ne /* Last Dword or differences. */ + cbz endloop, L(loop_aligned) + /* End of performance-critical section -- one 64B cache line. */ + + /* Not reached the limit, must have found a diff. */ + cbnz limit_wd, L(not_limit) + + /* Limit % 8 == 0 => all bytes significant. */ + ands limit, limit, #7 + b.eq L(not_limit) + + lsl limit, limit, #3 /* Bits -> bytes. */ + mov mask, #~0 +#ifdef __AARCH64EB__ + lsr mask, mask, limit +#else + lsl mask, mask, limit +#endif + bic data1, data1, mask + bic data2, data2, mask + + orr diff, diff, mask +L(not_limit): + +#ifndef __AARCH64EB__ + rev diff, diff + rev data1, data1 + rev data2, data2 +#endif + /* The MS-non-zero bit of DIFF marks either the first bit + that is different, or the end of the significant data. + Shifting left now will bring the critical information into the + top bits. */ + clz pos, diff + lsl data1, data1, pos + lsl data2, data2, pos + /* But we need to zero-extend (char is unsigned) the value and then + perform a signed 32-bit subtraction. */ + lsr data1, data1, #56 + sub result, data1, data2, lsr #56 + RET + +L(mutual_align): + /* Sources are mutually aligned, but are not currently at an + alignment boundary. Round down the addresses and then mask off + the bytes that precede the start point. */ + bic src1, src1, #7 + bic src2, src2, #7 + add limit, limit, tmp1 /* Adjust the limit for the extra. */ + lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ + ldr data1, [src1], #8 + neg tmp1, tmp1 /* Bits to alignment -64. */ + ldr data2, [src2], #8 + mov tmp2, #~0 +#ifdef __AARCH64EB__ + /* Big-endian. Early bytes are at MSB. */ + lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ +#else + /* Little-endian. Early bytes are at LSB. */ + lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ +#endif + add limit_wd, limit, #7 + orr data1, data1, tmp2 + orr data2, data2, tmp2 + lsr limit_wd, limit_wd, #3 + b L(start_realigned) + +L(ret0): + mov result, #0 + RET + + .p2align 6 +L(misaligned8): + sub limit, limit, #1 +1: + /* Perhaps we can do better than this. */ + ldrb data1w, [src1], #1 + ldrb data2w, [src2], #1 + subs limit, limit, #1 + ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ + b.eq 1b + sub result, data1, data2 + RET +END (memcmp) +#undef bcmp +weak_alias (memcmp, bcmp) +libc_hidden_builtin_def (memcmp) |