strlen.c File Reference

#include <limits.h>
#include <string.h>

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Macros
#define	LONGPTR_MASK   (sizeof(long) - 1)
#define	testbyte(x)

Functions
size_t	strlen (const char *str)
	Returns the length of the given null-terminated byte string. More...

Macro Definition Documentation

LONGPTR_MASK

#define LONGPTR_MASK   (sizeof(long) - 1)

Definition at line 64 of file strlen.c.

testbyte

#define testbyte

(

x

)

Value:

do                                                  \
    {                                                   \
        if(p[x] == '\0')                                \
            return ((uintptr_t)p - (uintptr_t)str + x); \
    } while(0)

Definition at line 70 of file strlen.c.

Function Documentation

strlen()

size_t strlen

(

const char *

str

)

Returns the length of the given null-terminated byte string.

Returns the length of the given null-terminated byte string, that is, the number of characters in a character array whose first element is pointed to by str up to and not including the first null character.

The behavior is undefined if str is not a pointer to a null-terminated byte string.

Parameters

str	pointer to the null-terminated byte string to be examined

Returns

The length of the null-terminated byte string str.

Definition at line 77 of file strlen.c.

{
    const char* p;
    const unsigned long* lp;

    /* Skip the first few bytes until we have an aligned p */
    for(p = str; (uintptr_t)p & LONGPTR_MASK; p++)
    {
        if(*p == '\0')
        {
            return ((uintptr_t)p - (uintptr_t)str);
        }
    }

    /* Scan the rest of the string using word sized operation */
    // Cast to void to prevent alignment warning
    for(lp = (const unsigned long*)(const void*)p;; lp++)
    {
        if((*lp - mask01) & mask80)
        {
            p = (const char*)(lp);
            testbyte(0);
            testbyte(1);
            testbyte(2);
            testbyte(3);
#if(LONG_BIT >= 64)
            testbyte(4);
            testbyte(5);
            testbyte(6);
            testbyte(7);
#endif
        }
    }

    /* NOTREACHED */
    // return (0);
}

References LONGPTR_MASK, and testbyte.

Referenced by __strchrnul(), strcat(), strcpy(), strdup(), strerror_r(), strncat(), strnstr(), strrchr(), and strxfrm().

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