memcpy() and memcpy2()

ANSI-C requires that the memcpy() library function in strings.h returns a pointer of the destination and handles and is able to also handle a count of zero:

Listing: Excerpts from the string.h and string.c files relating to memcpy()



/* extract of string.h *

extern void * memcpy(void *dest, const void * source, size_t count);

extern void  memcpy2(void *dest, const void * source, size_t count);

/* this function does not return dest and assumes count > 0 */

/* extract of string.c */

void * memcpy(void *dest, const void *source, size_t count) { 

  uchar *sd = dest;

  uchar *ss = source;

  while (count--)

    *sd++ = *ss++;

  return (dest);

}

If the function does not have to return the destination and it has to handle a count of zero, the memcpy2() function in the following listing is much simpler and faster:

Listing: Excerpts from the string.c File relating to memcpy2()



/* extract of string.c */

void

memcpy2(void *dest, const void* source, size_t count) {

  /* this func does not return dest and assumes count > 0 */

  do {

    *((uchar *)dest)++ = *((uchar*)source)++;

  } while(count--);

}

Replacing calls to memcpy() with calls to memcpy2() saves runtime and code size.