memchr.c File Reference

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

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Macros
#define	SS   (sizeof(size_t))
#define	ALIGN   (sizeof(size_t) - 1)
#define	ONES   ((size_t)-1 / UCHAR_MAX)
#define	HIGHS   (ONES * (UCHAR_MAX / 2 + 1))
#define	HASZERO(x)   ((x)-ONES & ~(x)&HIGHS)

Functions
void *	memchr (const void *src, int c, size_t n)
	Finds the first occurrence of c in the initial n characters of the object pointed to by s. More...

Macro Definition Documentation

ALIGN

#define ALIGN   (sizeof(size_t) - 1)

Definition at line 8 of file memchr.c.

HASZERO

#define HASZERO

(

x

)

((x)-ONES & ~(x)&HIGHS)

Definition at line 11 of file memchr.c.

HIGHS

#define HIGHS   (ONES * (UCHAR_MAX / 2 + 1))

Definition at line 10 of file memchr.c.

ONES

#define ONES   ((size_t)-1 / UCHAR_MAX)

Definition at line 9 of file memchr.c.

SS

#define SS   (sizeof(size_t))

Definition at line 7 of file memchr.c.

Function Documentation

memchr()

void* memchr	(	const void *	s,
		int	c,
		size_t	n
	)

Finds the first occurrence of c in the initial n characters of the object pointed to by s.

Finds the first occurrence of c (after conversion to unsigned char as if by (unsigned char)c ) in the initial n characters (each interpreted as unsigned char) of the object pointed to by s.

The behavior is undefined if access occurs beyond the end of the array (s) searched. The behavior is undefined if s is a null pointer.

Parameters

s	pointer to the object to be examined
c	character to search for
n	max number of characters to examine

Returns

a copy of dest

Definition at line 13 of file memchr.c.

{
    const unsigned char* s = src;
    c = (unsigned char)c;

#ifdef __GNUC__
    for(; ((uintptr_t)s & ALIGN) && n && *s != c; s++, n--)
    {
    }

    if(n && *s != c)
    {
        typedef size_t __attribute__((__may_alias__)) word;
        const word* w;
        size_t k = ONES * (size_t)c;

        for(w = (const void*)s; n >= SS && !HASZERO(*w ^ k); w++, n -= SS)
        {
        }

        s = (const void*)w;
    }
#endif

    for(; n && *s != c; s++, n--)
    {
    }

    return n ? (void*)(uintptr_t)s : 0;
}

References __attribute__(), ALIGN, HASZERO, ONES, and SS.

Referenced by memmem().

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