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/* strnlen - calculate the length of a string with limit.
Copyright (c) 2013, Linaro Limited
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
* Neither the name of the Linaro nor the
names of its contributors may be used to endorse or promote products
derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
#if (defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED))
/* See strlen-stub.c */
#else
/* Assumptions:
*
* ARMv8-a, AArch64
*/
/* Arguments and results. */
#define srcin x0
#define len x0
#define limit x1
/* Locals and temporaries. */
#define src x2
#define data1 x3
#define data2 x4
#define data2a x5
#define has_nul1 x6
#define has_nul2 x7
#define tmp1 x8
#define tmp2 x9
#define tmp3 x10
#define tmp4 x11
#define zeroones x12
#define pos x13
#define limit_wd x14
.macro def_fn f p2align=0
.text
.p2align \p2align
.global \f
.type \f, %function
\f:
.endm
#define REP8_01 0x0101010101010101
#define REP8_7f 0x7f7f7f7f7f7f7f7f
#define REP8_80 0x8080808080808080
.text
.p2align 6
.Lstart:
/* Pre-pad to ensure critical loop begins an icache line. */
.rep 7
nop
.endr
/* Put this code here to avoid wasting more space with pre-padding. */
.Lhit_limit:
mov len, limit
ret
def_fn 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. */
/* Start of critial section -- keep to one 64Byte cache line. */
.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
/* End of critical section -- keep to one 64Byte cache line. */
orr tmp1, has_nul1, has_nul2
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
#ifdef __AARCH64EB__
mov data2, data1
#endif
sub len, len, #8
mov has_nul2, has_nul1
.Lnul_in_data2:
#ifdef __AARCH64EB__
/* 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. */
rev data2, data2
sub tmp1, data2, zeroones
orr tmp2, data2, #REP8_7f
bic has_nul2, tmp1, tmp2
#endif
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. */
sub limit_wd, limit, #1
neg tmp4, tmp1
cmp tmp1, #8
and tmp3, limit_wd, #15
lsr limit_wd, limit_wd, #4
mov tmp2, #~0
ldp data1, data2, [src], #16
lsl tmp4, tmp4, #3 /* Bytes beyond alignment -> bits. */
add tmp3, tmp3, tmp1
#ifdef __AARCH64EB__
/* Big-endian. Early bytes are at MSB. */
lsl tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */
#else
/* Little-endian. Early bytes are at LSB. */
lsr tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */
#endif
add limit_wd, limit_wd, tmp3, lsr #4
orr data1, data1, tmp2
orr data2a, data2, tmp2
csinv data1, data1, xzr, le
csel data2, data2, data2a, le
b .Lrealigned
.size strnlen, . - .Lstart /* Include pre-padding in size. */
#endif
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