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Diffstat (limited to 'libc/arch-arm/bionic/strlen.c')
| -rw-r--r-- | libc/arch-arm/bionic/strlen.c | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/libc/arch-arm/bionic/strlen.c b/libc/arch-arm/bionic/strlen.c new file mode 100644 index 0000000..3d1fe45 --- /dev/null +++ b/libc/arch-arm/bionic/strlen.c @@ -0,0 +1,126 @@ +/* + * Copyright (C) 2008 The Android Open Source Project + * 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. + * + * 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 OWNER 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. + */ +#include <string.h> +#include <stdint.h> + +size_t strlen(const char *s) +{ + __builtin_prefetch(s); + __builtin_prefetch(s+32); + + union { + const char *b; + const uint32_t *w; + uintptr_t i; + } u; + + // these are some scratch variables for the asm code below + uint32_t v, t; + + // initialize the string length to zero + size_t l = 0; + + // align the pointer to a 32-bit word boundary + u.b = s; + while (u.i & 0x3) { + if (__builtin_expect(*u.b++ == 0, 0)) { + goto done; + } + l++; + } + + // loop for each word, testing if it contains a zero byte + // if so, exit the loop and update the length. + // We need to process 32 bytes per loop to schedule PLD properly + // and achieve the maximum bus speed. + asm( + "ldr %[v], [ %[s] ], #4 \n" + "sub %[l], %[l], %[s] \n" + "0: \n" + "pld [ %[s], #64 ] \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" +#if !defined(__OPTIMIZE_SIZE__) + "bne 1f \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" + "bne 1f \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" + "bne 1f \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" + "bne 1f \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" + "bne 1f \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" + "bne 1f \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" + "bne 1f \n" + "sub %[t], %[v], %[mask], lsr #7\n" + "and %[t], %[t], %[mask] \n" + "bics %[t], %[t], %[v] \n" + "ldreq %[v], [ %[s] ], #4 \n" +#endif + "beq 0b \n" + "1: \n" + "add %[l], %[l], %[s] \n" + "tst %[v], #0xFF \n" + "beq 2f \n" + "add %[l], %[l], #1 \n" + "tst %[v], #0xFF00 \n" + "beq 2f \n" + "add %[l], %[l], #1 \n" + "tst %[v], #0xFF0000 \n" + "addne %[l], %[l], #1 \n" + "2: \n" + : [l]"=&r"(l), [v]"=&r"(v), [t]"=&r"(t), [s]"=&r"(u.b) + : "%[l]"(l), "%[s]"(u.b), [mask]"r"(0x80808080UL) + : "cc" + ); + +done: + return l; +} |