diff options
Diffstat (limited to 'cpukit/libc/string/strlen.c')
-rw-r--r-- | cpukit/libc/string/strlen.c | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/cpukit/libc/string/strlen.c b/cpukit/libc/string/strlen.c new file mode 100644 index 0000000000..acffa49e14 --- /dev/null +++ b/cpukit/libc/string/strlen.c @@ -0,0 +1,82 @@ +/* +FUNCTION + <<strlen>>---character string length + +INDEX + strlen + +SYNOPSIS + #include <string.h> + size_t strlen(const char *<[str]>); + +DESCRIPTION + The <<strlen>> function works out the length of the string + starting at <<*<[str]>>> by counting chararacters until it + reaches a <<NULL>> character. + +RETURNS + <<strlen>> returns the character count. + +PORTABILITY +<<strlen>> is ANSI C. + +<<strlen>> requires no supporting OS subroutines. + +QUICKREF + strlen ansi pure +*/ + +#include <_ansi.h> +#include <string.h> +#include <limits.h> + +#define LBLOCKSIZE (sizeof (long)) +#define UNALIGNED(X) ((long)X & (LBLOCKSIZE - 1)) + +#if LONG_MAX == 2147483647L +#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080) +#else +#if LONG_MAX == 9223372036854775807L +/* Nonzero if X (a long int) contains a NULL byte. */ +#define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080) +#else +#error long int is not a 32bit or 64bit type. +#endif +#endif + +#ifndef DETECTNULL +#error long int is not a 32bit or 64bit byte +#endif + +size_t +strlen (const char *str) +{ + const char *start = str; + +#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__) + unsigned long *aligned_addr; + + /* Align the pointer, so we can search a word at a time. */ + while (UNALIGNED (str)) + { + if (!*str) + return str - start; + str++; + } + + /* If the string is word-aligned, we can check for the presence of + a null in each word-sized block. */ + aligned_addr = (unsigned long *)str; + while (!DETECTNULL (*aligned_addr)) + aligned_addr++; + + /* Once a null is detected, we check each byte in that block for a + precise position of the null. */ + str = (char *) aligned_addr; + +#endif /* not PREFER_SIZE_OVER_SPEED */ + + while (*str) + str++; + return str - start; +} |