stpncpy.c raw

   1  #include <string.h>
   2  #include <stdint.h>
   3  #include <limits.h>
   4  
   5  #define ALIGN (sizeof(size_t)-1)
   6  #define ONES ((size_t)-1/UCHAR_MAX)
   7  #define HIGHS (ONES * (UCHAR_MAX/2+1))
   8  #define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
   9  
  10  char *__stpncpy(char *restrict d, const char *restrict s, size_t n)
  11  {
  12  #ifdef __GNUC__
  13  	typedef size_t __attribute__((__may_alias__)) word;
  14  	word *wd;
  15  	const word *ws;
  16  	if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
  17  		for (; ((uintptr_t)s & ALIGN) && n && (*d=*s); n--, s++, d++);
  18  		if (!n || !*s) goto tail;
  19  		wd=(void *)d; ws=(const void *)s;
  20  		for (; n>=sizeof(size_t) && !HASZERO(*ws);
  21  		       n-=sizeof(size_t), ws++, wd++) *wd = *ws;
  22  		d=(void *)wd; s=(const void *)ws;
  23  	}
  24  #endif
  25  	for (; n && (*d=*s); n--, s++, d++);
  26  tail:
  27  	memset(d, 0, n);
  28  	return d;
  29  }
  30  
  31  weak_alias(__stpncpy, stpncpy);
  32  
  33