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77 lines
3.0 KiB
ArmAsm
77 lines
3.0 KiB
ArmAsm
/* Copyright (C) 1998-2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<https://www.gnu.org/licenses/>. */
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/* Thumb requires excessive IT insns here. */
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#define NO_THUMB
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#include <sysdep.h>
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/* size_t strlen(const char *S)
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* entry: r0 -> string
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* exit: r0 = len
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*/
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.syntax unified
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.text
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ENTRY(strlen)
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bic r1, r0, $3 @ addr of word containing first byte
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ldr r2, [r1], $4 @ get the first word
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ands r3, r0, $3 @ how many bytes are duff?
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rsb r0, r3, $0 @ get - that number into counter.
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beq Laligned @ skip into main check routine if no
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@ more
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#ifdef __ARMEB__
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orr r2, r2, $0xff000000 @ set this byte to non-zero
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subs r3, r3, $1 @ any more to do?
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orrgt r2, r2, $0x00ff0000 @ if so, set this byte
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subs r3, r3, $1 @ more?
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orrgt r2, r2, $0x0000ff00 @ then set.
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#else
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orr r2, r2, $0x000000ff @ set this byte to non-zero
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subs r3, r3, $1 @ any more to do?
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orrgt r2, r2, $0x0000ff00 @ if so, set this byte
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subs r3, r3, $1 @ more?
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orrgt r2, r2, $0x00ff0000 @ then set.
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#endif
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Laligned: @ here, we have a word in r2. Does it
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tst r2, $0x000000ff @ contain any zeroes?
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tstne r2, $0x0000ff00 @
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tstne r2, $0x00ff0000 @
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tstne r2, $0xff000000 @
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addne r0, r0, $4 @ if not, the string is 4 bytes longer
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ldrne r2, [r1], $4 @ and we continue to the next word
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bne Laligned @
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Llastword: @ drop through to here once we find a
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#ifdef __ARMEB__
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tst r2, $0xff000000 @ word that has a zero byte in it
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addne r0, r0, $1 @
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tstne r2, $0x00ff0000 @ and add up to 3 bytes on to it
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addne r0, r0, $1 @
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tstne r2, $0x0000ff00 @ (if first three all non-zero, 4th
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addne r0, r0, $1 @ must be zero)
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#else
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tst r2, $0x000000ff @ word that has a zero byte in it
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addne r0, r0, $1 @
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tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
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addne r0, r0, $1 @
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tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
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addne r0, r0, $1 @ must be zero)
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#endif
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DO_RET(lr)
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END(strlen)
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libc_hidden_builtin_def (strlen)
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