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Diffstat (limited to 'arch/arm64/lib/strlen.S')
| -rw-r--r-- | arch/arm64/lib/strlen.S | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/arch/arm64/lib/strlen.S b/arch/arm64/lib/strlen.S new file mode 100644 index 000000000000..987b68b9ce44 --- /dev/null +++ b/arch/arm64/lib/strlen.S @@ -0,0 +1,126 @@ +/* + * Copyright (C) 2013 ARM Ltd. + * Copyright (C) 2013 Linaro. + * + * This code is based on glibc cortex strings work originally authored by Linaro + * and re-licensed under GPLv2 for the Linux kernel. The original code can + * be found @ + * + * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/ + * files/head:/src/aarch64/ + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ + +#include <linux/linkage.h> +#include <asm/assembler.h> + +/* + * calculate the length of a string + * + * Parameters: + * x0 - const string pointer + * Returns: + * x0 - the return length of specific string + */ + +/* Arguments and results. */ +srcin .req x0 +len .req x0 + +/* Locals and temporaries. */ +src .req x1 +data1 .req x2 +data2 .req x3 +data2a .req x4 +has_nul1 .req x5 +has_nul2 .req x6 +tmp1 .req x7 +tmp2 .req x8 +tmp3 .req x9 +tmp4 .req x10 +zeroones .req x11 +pos .req x12 + +#define REP8_01 0x0101010101010101 +#define REP8_7f 0x7f7f7f7f7f7f7f7f +#define REP8_80 0x8080808080808080 + +ENTRY(strlen) + mov zeroones, #REP8_01 + bic src, srcin, #15 + ands tmp1, srcin, #15 + b.ne .Lmisaligned + /* + * NUL detection works on the principle that (X - 1) & (~X) & 0x80 + * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and + * can be done in parallel across the entire word. + */ + /* + * The inner loop deals with two Dwords at a time. This has a + * slightly higher start-up cost, but we should win quite quickly, + * especially on cores with a high number of issue slots per + * cycle, as we get much better parallelism out of the operations. + */ +.Lloop: + ldp data1, data2, [src], #16 +.Lrealigned: + sub tmp1, data1, zeroones + orr tmp2, data1, #REP8_7f + sub tmp3, data2, zeroones + orr tmp4, data2, #REP8_7f + bic has_nul1, tmp1, tmp2 + bics has_nul2, tmp3, tmp4 + ccmp has_nul1, #0, #0, eq /* NZCV = 0000 */ + b.eq .Lloop + + sub len, src, srcin + cbz has_nul1, .Lnul_in_data2 +CPU_BE( mov data2, data1 ) /*prepare data to re-calculate the syndrome*/ + sub len, len, #8 + mov has_nul2, has_nul1 +.Lnul_in_data2: + /* + * For big-endian, carry propagation (if the final byte in the + * string is 0x01) means we cannot use has_nul directly. The + * easiest way to get the correct byte is to byte-swap the data + * and calculate the syndrome a second time. + */ +CPU_BE( rev data2, data2 ) +CPU_BE( sub tmp1, data2, zeroones ) +CPU_BE( orr tmp2, data2, #REP8_7f ) +CPU_BE( bic has_nul2, tmp1, tmp2 ) + + sub len, len, #8 + rev has_nul2, has_nul2 + clz pos, has_nul2 + add len, len, pos, lsr #3 /* Bits to bytes. */ + ret + +.Lmisaligned: + cmp tmp1, #8 + neg tmp1, tmp1 + ldp data1, data2, [src], #16 + lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ + mov tmp2, #~0 + /* Big-endian. Early bytes are at MSB. */ +CPU_BE( lsl tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */ + /* Little-endian. Early bytes are at LSB. */ +CPU_LE( lsr tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */ + + orr data1, data1, tmp2 + orr data2a, data2, tmp2 + csinv data1, data1, xzr, le + csel data2, data2, data2a, le + b .Lrealigned +ENDPROC(strlen) |