diff options
Diffstat (limited to 'ports/sysdeps/arm/armv6/strlen.S')
| -rw-r--r-- | ports/sysdeps/arm/armv6/strlen.S | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/ports/sysdeps/arm/armv6/strlen.S b/ports/sysdeps/arm/armv6/strlen.S new file mode 100644 index 0000000000..a53d41418a --- /dev/null +++ b/ports/sysdeps/arm/armv6/strlen.S @@ -0,0 +1,99 @@ +/* strlen -- find the length of a nul-terminated string. + Copyright (C) 2013 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library. If not, see + <http://www.gnu.org/licenses/>. */ + +#include <sysdep.h> + + .syntax unified + .text + +ENTRY (strlen) + @ r0 = start of string + ldrb r2, [r0] @ load the first byte asap + + @ To cater to long strings, we want to search through a few + @ characters until we reach an aligned pointer. To cater to + @ small strings, we don't want to start doing word operations + @ immediately. The compromise is a maximum of 16 bytes less + @ whatever is required to end with an aligned pointer. + @ r3 = number of characters to search in alignment loop + and r3, r0, #7 + mov r1, r0 @ Save the input pointer + rsb r3, r3, #15 @ 16 - 1 peeled loop iteration + cmp r2, #0 + beq 99f + + @ Loop until we find ... +1: ldrb r2, [r0, #1]! + subs r3, r3, #1 @ ... the aligment point + it ne + cmpne r2, #0 @ ... or EOS + bne 1b + + @ Disambiguate the exit possibilites above + cmp r2, #0 @ Found EOS + beq 99f + add r0, r0, #1 + + @ So now we're aligned. + ldrd r2, r3, [r0], #8 +#ifdef ARCH_HAS_T2 + movw ip, #0x0101 + pld [r0, #64] + movt ip, #0x0101 +#else + ldr ip, =0x01010101 + pld [r0, #64] +#endif + + @ Loop searching for EOS, 8 bytes at a time. + @ Subtracting (unsigned saturating) from 1 for any byte means that + @ we get 1 for any byte that was originally zero and 0 otherwise. + @ Therefore we consider the lsb of each byte the "found" bit. + .balign 16 +2: uqsub8 r2, ip, r2 @ Find EOS + uqsub8 r3, ip, r3 + pld [r0, #128] @ Prefetch 2 lines ahead + orrs r3, r3, r2 @ Combine the two words + it eq + ldrdeq r2, r3, [r0], #8 + beq 2b + + @ Found something. Disambiguate between first and second words. + @ Adjust r0 to point to the word containing the match. + @ Adjust r2 to the found bits for the word containing the match. + cmp r2, #0 + sub r0, r0, #4 + ite eq + moveq r2, r3 + subne r0, r0, #4 + + @ Find the bit-offset of the match within the word. Note that the + @ bit result from clz will be 7 higher than "true", but we'll + @ immediately discard those bits converting to a byte offset. +#ifdef __ARMEL__ + rev r2, r2 @ For LE, count from the little end +#endif + clz r2, r2 + add r0, r0, r2, lsr #3 @ Adjust the pointer to the found byte +99: + sub r0, r0, r1 @ Subtract input to compute length + bx lr + +END (strlen) + +libc_hidden_builtin_def (strlen) |