Function lpPrev

src/listpack.c:466–475

If 'p' points to an element of the listpack, calling lpPrev() will return * the pointer to the previous element (the one on the left), or NULL if 'p' * already pointed to the first element of the listpack. */

 * the pointer to the previous element (the one on the left), or NULL if 'p'
 * already pointed to the first element of the listpack. */
unsigned char *lpPrev(unsigned char *lp, unsigned char *p) {
    assert(p);
    if (p-lp == LP_HDR_SIZE) return NULL;
    p--; /* Seek the first backlen byte of the last element. */
    uint64_t prevlen = lpDecodeBacklen(p);
    prevlen += lpEncodeBacklen(NULL,prevlen);
    p -= prevlen-1; /* Seek the first byte of the previous entry. */
    lpAssertValidEntry(lp, lpBytes(lp), p);
    return p;
}

/* Return a pointer to the first element of the listpack, or NULL if the
 * listpack has no elements. */