1*043036a2SApple OSS Distributions /*-
2*043036a2SApple OSS Distributions * Copyright (c) 2009 Xin LI <[email protected]>
3*043036a2SApple OSS Distributions * All rights reserved.
4*043036a2SApple OSS Distributions *
5*043036a2SApple OSS Distributions * Redistribution and use in source and binary forms, with or without
6*043036a2SApple OSS Distributions * modification, are permitted provided that the following conditions
7*043036a2SApple OSS Distributions * are met:
8*043036a2SApple OSS Distributions * 1. Redistributions of source code must retain the above copyright
9*043036a2SApple OSS Distributions * notice, this list of conditions and the following disclaimer.
10*043036a2SApple OSS Distributions * 2. Redistributions in binary form must reproduce the above copyright
11*043036a2SApple OSS Distributions * notice, this list of conditions and the following disclaimer in the
12*043036a2SApple OSS Distributions * documentation and/or other materials provided with the distribution.
13*043036a2SApple OSS Distributions *
14*043036a2SApple OSS Distributions * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15*043036a2SApple OSS Distributions * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16*043036a2SApple OSS Distributions * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17*043036a2SApple OSS Distributions * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18*043036a2SApple OSS Distributions * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19*043036a2SApple OSS Distributions * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20*043036a2SApple OSS Distributions * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21*043036a2SApple OSS Distributions * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22*043036a2SApple OSS Distributions * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23*043036a2SApple OSS Distributions * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24*043036a2SApple OSS Distributions * SUCH DAMAGE.
25*043036a2SApple OSS Distributions */
26*043036a2SApple OSS Distributions
27*043036a2SApple OSS Distributions #include "string.h"
28*043036a2SApple OSS Distributions #include <limits.h>
29*043036a2SApple OSS Distributions
30*043036a2SApple OSS Distributions /*
31*043036a2SApple OSS Distributions * Portable strlen() for 32-bit and 64-bit systems.
32*043036a2SApple OSS Distributions *
33*043036a2SApple OSS Distributions * Rationale: it is generally much more efficient to do word length
34*043036a2SApple OSS Distributions * operations and avoid branches on modern computer systems, as
35*043036a2SApple OSS Distributions * compared to byte-length operations with a lot of branches.
36*043036a2SApple OSS Distributions *
37*043036a2SApple OSS Distributions * The expression:
38*043036a2SApple OSS Distributions *
39*043036a2SApple OSS Distributions * ((x - 0x01....01) & ~x & 0x80....80)
40*043036a2SApple OSS Distributions *
41*043036a2SApple OSS Distributions * would evaluate to a non-zero value iff any of the bytes in the
42*043036a2SApple OSS Distributions * original word is zero. However, we can further reduce ~1/3 of
43*043036a2SApple OSS Distributions * time if we consider that strlen() usually operate on 7-bit ASCII
44*043036a2SApple OSS Distributions * by employing the following expression, which allows false positive
45*043036a2SApple OSS Distributions * when high bit of 1 and use the tail case to catch these case:
46*043036a2SApple OSS Distributions *
47*043036a2SApple OSS Distributions * ((x - 0x01....01) & 0x80....80)
48*043036a2SApple OSS Distributions *
49*043036a2SApple OSS Distributions * This is more than 5.2 times as fast as the raw implementation on
50*043036a2SApple OSS Distributions * Intel T7300 under long mode for strings longer than word length.
51*043036a2SApple OSS Distributions */
52*043036a2SApple OSS Distributions
53*043036a2SApple OSS Distributions /* Magic numbers for the algorithm */
54*043036a2SApple OSS Distributions #if LONG_BIT == 32
55*043036a2SApple OSS Distributions static const unsigned long mask01 = 0x01010101;
56*043036a2SApple OSS Distributions static const unsigned long mask80 = 0x80808080;
57*043036a2SApple OSS Distributions #elif LONG_BIT == 64
58*043036a2SApple OSS Distributions static const unsigned long mask01 = 0x0101010101010101;
59*043036a2SApple OSS Distributions static const unsigned long mask80 = 0x8080808080808080;
60*043036a2SApple OSS Distributions #else
61*043036a2SApple OSS Distributions #error Unsupported word size
62*043036a2SApple OSS Distributions #endif
63*043036a2SApple OSS Distributions
64*043036a2SApple OSS Distributions #define LONGPTR_MASK (sizeof(long) - 1)
65*043036a2SApple OSS Distributions
66*043036a2SApple OSS Distributions /*
67*043036a2SApple OSS Distributions * Helper macro to return string length if we caught the zero
68*043036a2SApple OSS Distributions * byte.
69*043036a2SApple OSS Distributions */
70*043036a2SApple OSS Distributions #define testbyte(x) \
71*043036a2SApple OSS Distributions do { \
72*043036a2SApple OSS Distributions if (p[x] == '\0') \
73*043036a2SApple OSS Distributions return (p - str + x); \
74*043036a2SApple OSS Distributions } while (0)
75*043036a2SApple OSS Distributions
76*043036a2SApple OSS Distributions __attribute__((visibility("hidden")))
77*043036a2SApple OSS Distributions size_t
_libkernel_strlen(const char * str)78*043036a2SApple OSS Distributions _libkernel_strlen(const char *str)
79*043036a2SApple OSS Distributions {
80*043036a2SApple OSS Distributions const char *p;
81*043036a2SApple OSS Distributions const unsigned long *lp;
82*043036a2SApple OSS Distributions
83*043036a2SApple OSS Distributions /* Skip the first few bytes until we have an aligned p */
84*043036a2SApple OSS Distributions for (p = str; (uintptr_t)p & LONGPTR_MASK; p++) {
85*043036a2SApple OSS Distributions if (*p == '\0') {
86*043036a2SApple OSS Distributions return p - str;
87*043036a2SApple OSS Distributions }
88*043036a2SApple OSS Distributions }
89*043036a2SApple OSS Distributions
90*043036a2SApple OSS Distributions /* Scan the rest of the string using word sized operation */
91*043036a2SApple OSS Distributions for (lp = (const unsigned long *)p;; lp++) {
92*043036a2SApple OSS Distributions if ((*lp - mask01) & mask80) {
93*043036a2SApple OSS Distributions p = (const char *)(lp);
94*043036a2SApple OSS Distributions testbyte(0);
95*043036a2SApple OSS Distributions testbyte(1);
96*043036a2SApple OSS Distributions testbyte(2);
97*043036a2SApple OSS Distributions testbyte(3);
98*043036a2SApple OSS Distributions #if (LONG_BIT >= 64)
99*043036a2SApple OSS Distributions testbyte(4);
100*043036a2SApple OSS Distributions testbyte(5);
101*043036a2SApple OSS Distributions testbyte(6);
102*043036a2SApple OSS Distributions testbyte(7);
103*043036a2SApple OSS Distributions #endif
104*043036a2SApple OSS Distributions }
105*043036a2SApple OSS Distributions }
106*043036a2SApple OSS Distributions
107*043036a2SApple OSS Distributions /* NOTREACHED */
108*043036a2SApple OSS Distributions return 0;
109*043036a2SApple OSS Distributions }
110