mirror of
https://github.com/autc04/Retro68.git
synced 2024-12-01 11:52:47 +00:00
239 lines
7.6 KiB
ArmAsm
239 lines
7.6 KiB
ArmAsm
/* Copyright (c) 2013-2015, 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, unaligned accesses, min page size 4k.
|
|
*/
|
|
|
|
/* To test the page crossing code path more thoroughly, compile with
|
|
-DTEST_PAGE_CROSS - this will force all calls through the slower
|
|
entry path. This option is not intended for production use. */
|
|
|
|
/* Arguments and results. */
|
|
#define srcin x0
|
|
#define len x0
|
|
|
|
/* Locals and temporaries. */
|
|
#define src x1
|
|
#define data1 x2
|
|
#define data2 x3
|
|
#define has_nul1 x4
|
|
#define has_nul2 x5
|
|
#define tmp1 x4
|
|
#define tmp2 x5
|
|
#define tmp3 x6
|
|
#define tmp4 x7
|
|
#define zeroones x8
|
|
|
|
#define L(l) .L ## l
|
|
|
|
.macro def_fn f p2align=0
|
|
.text
|
|
.p2align \p2align
|
|
.global \f
|
|
.type \f, %function
|
|
\f:
|
|
.endm
|
|
|
|
/* 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. A faster check
|
|
(X - 1) & 0x80 is zero for non-NUL ASCII characters, but gives
|
|
false hits for characters 129..255. */
|
|
|
|
#define REP8_01 0x0101010101010101
|
|
#define REP8_7f 0x7f7f7f7f7f7f7f7f
|
|
#define REP8_80 0x8080808080808080
|
|
|
|
#ifdef TEST_PAGE_CROSS
|
|
# define MIN_PAGE_SIZE 15
|
|
#else
|
|
# define MIN_PAGE_SIZE 4096
|
|
#endif
|
|
|
|
/* Since strings are short on average, we check the first 16 bytes
|
|
of the string for a NUL character. In order to do an unaligned ldp
|
|
safely we have to do a page cross check first. If there is a NUL
|
|
byte we calculate the length from the 2 8-byte words using
|
|
conditional select to reduce branch mispredictions (it is unlikely
|
|
strlen will be repeatedly called on strings with the same length).
|
|
|
|
If the string is longer than 16 bytes, we align src so don't need
|
|
further page cross checks, and process 32 bytes per iteration
|
|
using the fast NUL check. If we encounter non-ASCII characters,
|
|
fallback to a second loop using the full NUL check.
|
|
|
|
If the page cross check fails, we read 16 bytes from an aligned
|
|
address, remove any characters before the string, and continue
|
|
in the main loop using aligned loads. Since strings crossing a
|
|
page in the first 16 bytes are rare (probability of
|
|
16/MIN_PAGE_SIZE ~= 0.4%), this case does not need to be optimized.
|
|
|
|
AArch64 systems have a minimum page size of 4k. We don't bother
|
|
checking for larger page sizes - the cost of setting up the correct
|
|
page size is just not worth the extra gain from a small reduction in
|
|
the cases taking the slow path. Note that we only care about
|
|
whether the first fetch, which may be misaligned, crosses a page
|
|
boundary. */
|
|
|
|
def_fn strlen p2align=6
|
|
and tmp1, srcin, MIN_PAGE_SIZE - 1
|
|
mov zeroones, REP8_01
|
|
cmp tmp1, MIN_PAGE_SIZE - 16
|
|
b.gt L(page_cross)
|
|
ldp data1, data2, [srcin]
|
|
#ifdef __AARCH64EB__
|
|
/* For big-endian, carry propagation (if the final byte in the
|
|
string is 0x01) means we cannot use has_nul1/2 directly.
|
|
Since we expect strings to be small and early-exit,
|
|
byte-swap the data now so has_null1/2 will be correct. */
|
|
rev data1, data1
|
|
rev data2, data2
|
|
#endif
|
|
sub tmp1, data1, zeroones
|
|
orr tmp2, data1, REP8_7f
|
|
sub tmp3, data2, zeroones
|
|
orr tmp4, data2, REP8_7f
|
|
bics has_nul1, tmp1, tmp2
|
|
bic has_nul2, tmp3, tmp4
|
|
ccmp has_nul2, 0, 0, eq
|
|
beq L(main_loop_entry)
|
|
|
|
/* Enter with C = has_nul1 == 0. */
|
|
csel has_nul1, has_nul1, has_nul2, cc
|
|
mov len, 8
|
|
rev has_nul1, has_nul1
|
|
clz tmp1, has_nul1
|
|
csel len, xzr, len, cc
|
|
add len, len, tmp1, lsr 3
|
|
ret
|
|
|
|
/* The inner loop processes 32 bytes per iteration and uses the fast
|
|
NUL check. If we encounter non-ASCII characters, use a second
|
|
loop with the accurate NUL check. */
|
|
.p2align 4
|
|
L(main_loop_entry):
|
|
bic src, srcin, 15
|
|
sub src, src, 16
|
|
L(main_loop):
|
|
ldp data1, data2, [src, 32]!
|
|
.Lpage_cross_entry:
|
|
sub tmp1, data1, zeroones
|
|
sub tmp3, data2, zeroones
|
|
orr tmp2, tmp1, tmp3
|
|
tst tmp2, zeroones, lsl 7
|
|
bne 1f
|
|
ldp data1, data2, [src, 16]
|
|
sub tmp1, data1, zeroones
|
|
sub tmp3, data2, zeroones
|
|
orr tmp2, tmp1, tmp3
|
|
tst tmp2, zeroones, lsl 7
|
|
beq L(main_loop)
|
|
add src, src, 16
|
|
1:
|
|
/* The fast check failed, so do the slower, accurate NUL check. */
|
|
orr tmp2, data1, REP8_7f
|
|
orr tmp4, data2, REP8_7f
|
|
bics has_nul1, tmp1, tmp2
|
|
bic has_nul2, tmp3, tmp4
|
|
ccmp has_nul2, 0, 0, eq
|
|
beq L(nonascii_loop)
|
|
|
|
/* Enter with C = has_nul1 == 0. */
|
|
L(tail):
|
|
#ifdef __AARCH64EB__
|
|
/* For big-endian, carry propagation (if the final byte in the
|
|
string is 0x01) means we cannot use has_nul1/2 directly. The
|
|
easiest way to get the correct byte is to byte-swap the data
|
|
and calculate the syndrome a second time. */
|
|
csel data1, data1, data2, cc
|
|
rev data1, data1
|
|
sub tmp1, data1, zeroones
|
|
orr tmp2, data1, REP8_7f
|
|
bic has_nul1, tmp1, tmp2
|
|
#else
|
|
csel has_nul1, has_nul1, has_nul2, cc
|
|
#endif
|
|
sub len, src, srcin
|
|
rev has_nul1, has_nul1
|
|
add tmp2, len, 8
|
|
clz tmp1, has_nul1
|
|
csel len, len, tmp2, cc
|
|
add len, len, tmp1, lsr 3
|
|
ret
|
|
|
|
L(nonascii_loop):
|
|
ldp data1, data2, [src, 16]!
|
|
sub tmp1, data1, zeroones
|
|
orr tmp2, data1, REP8_7f
|
|
sub tmp3, data2, zeroones
|
|
orr tmp4, data2, REP8_7f
|
|
bics has_nul1, tmp1, tmp2
|
|
bic has_nul2, tmp3, tmp4
|
|
ccmp has_nul2, 0, 0, eq
|
|
bne L(tail)
|
|
ldp data1, data2, [src, 16]!
|
|
sub tmp1, data1, zeroones
|
|
orr tmp2, data1, REP8_7f
|
|
sub tmp3, data2, zeroones
|
|
orr tmp4, data2, REP8_7f
|
|
bics has_nul1, tmp1, tmp2
|
|
bic has_nul2, tmp3, tmp4
|
|
ccmp has_nul2, 0, 0, eq
|
|
beq L(nonascii_loop)
|
|
b L(tail)
|
|
|
|
/* Load 16 bytes from [srcin & ~15] and force the bytes that precede
|
|
srcin to 0x7f, so we ignore any NUL bytes before the string.
|
|
Then continue in the aligned loop. */
|
|
L(page_cross):
|
|
bic src, srcin, 15
|
|
ldp data1, data2, [src]
|
|
lsl tmp1, srcin, 3
|
|
mov tmp4, -1
|
|
#ifdef __AARCH64EB__
|
|
/* Big-endian. Early bytes are at MSB. */
|
|
lsr tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */
|
|
#else
|
|
/* Little-endian. Early bytes are at LSB. */
|
|
lsl tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */
|
|
#endif
|
|
orr tmp1, tmp1, REP8_80
|
|
orn data1, data1, tmp1
|
|
orn tmp2, data2, tmp1
|
|
tst srcin, 8
|
|
csel data1, data1, tmp4, eq
|
|
csel data2, data2, tmp2, eq
|
|
b L(page_cross_entry)
|
|
|
|
.size strlen, . - strlen
|
|
#endif
|