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Diffstat (limited to 'arch/arm64/lib/strnlen.S')
| -rw-r--r-- | arch/arm64/lib/strnlen.S | 171 |
1 files changed, 171 insertions, 0 deletions
diff --git a/arch/arm64/lib/strnlen.S b/arch/arm64/lib/strnlen.S new file mode 100644 index 000000000..355be0444 --- /dev/null +++ b/arch/arm64/lib/strnlen.S @@ -0,0 +1,171 @@ +/* + * 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> + +/* + * determine the length of a fixed-size string + * + * Parameters: + * x0 - const string pointer + * x1 - maximal string length + * Returns: + * x0 - the return length of specific string + */ + +/* Arguments and results. */ +srcin .req x0 +len .req x0 +limit .req x1 + +/* Locals and temporaries. */ +src .req x2 +data1 .req x3 +data2 .req x4 +data2a .req x5 +has_nul1 .req x6 +has_nul2 .req x7 +tmp1 .req x8 +tmp2 .req x9 +tmp3 .req x10 +tmp4 .req x11 +zeroones .req x12 +pos .req x13 +limit_wd .req x14 + +#define REP8_01 0x0101010101010101 +#define REP8_7f 0x7f7f7f7f7f7f7f7f +#define REP8_80 0x8080808080808080 + +WEAK(strnlen) + cbz limit, .Lhit_limit + mov zeroones, #REP8_01 + bic src, srcin, #15 + ands tmp1, srcin, #15 + b.ne .Lmisaligned + /* Calculate the number of full and partial words -1. */ + sub limit_wd, limit, #1 /* Limit != 0, so no underflow. */ + lsr limit_wd, limit_wd, #4 /* Convert to Qwords. */ + + /* + * 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 + bic has_nul2, tmp3, tmp4 + subs limit_wd, limit_wd, #1 + orr tmp1, has_nul1, has_nul2 + ccmp tmp1, #0, #0, pl /* NZCV = 0000 */ + b.eq .Lloop + + cbz tmp1, .Lhit_limit /* No null in final Qword. */ + + /* + * We know there's a null in the final Qword. The easiest thing + * to do now is work out the length of the string and return + * MIN (len, limit). + */ + sub len, src, srcin + cbz has_nul1, .Lnul_in_data2 +CPU_BE( mov data2, data1 ) /*perpare 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. */ + cmp len, limit + csel len, len, limit, ls /* Return the lower value. */ + ret + +.Lmisaligned: + /* + * Deal with a partial first word. + * We're doing two things in parallel here; + * 1) Calculate the number of words (but avoiding overflow if + * limit is near ULONG_MAX) - to do this we need to work out + * limit + tmp1 - 1 as a 65-bit value before shifting it; + * 2) Load and mask the initial data words - we force the bytes + * before the ones we are interested in to 0xff - this ensures + * early bytes will not hit any zero detection. + */ + ldp data1, data2, [src], #16 + + sub limit_wd, limit, #1 + and tmp3, limit_wd, #15 + lsr limit_wd, limit_wd, #4 + + add tmp3, tmp3, tmp1 + add limit_wd, limit_wd, tmp3, lsr #4 + + neg tmp4, tmp1 + lsl tmp4, tmp4, #3 /* Bytes beyond alignment -> bits. */ + + mov tmp2, #~0 + /* Big-endian. Early bytes are at MSB. */ +CPU_BE( lsl tmp2, tmp2, tmp4 ) /* Shift (tmp1 & 63). */ + /* Little-endian. Early bytes are at LSB. */ +CPU_LE( lsr tmp2, tmp2, tmp4 ) /* Shift (tmp1 & 63). */ + + cmp tmp1, #8 + + orr data1, data1, tmp2 + orr data2a, data2, tmp2 + + csinv data1, data1, xzr, le + csel data2, data2, data2a, le + b .Lrealigned + +.Lhit_limit: + mov len, limit + ret +ENDPIPROC(strnlen) |