diff options
| -rw-r--r-- | erts/emulator/beam/erl_bif_lists.c | 93 |
1 files changed, 77 insertions, 16 deletions
diff --git a/erts/emulator/beam/erl_bif_lists.c b/erts/emulator/beam/erl_bif_lists.c index fe64e76575..647a218851 100644 --- a/erts/emulator/beam/erl_bif_lists.c +++ b/erts/emulator/beam/erl_bif_lists.c @@ -40,32 +40,93 @@ static BIF_RETTYPE append(Process* p, Eterm A, Eterm B) Eterm list; Eterm copy; Eterm last; - size_t need; - Eterm* hp; + Eterm* hp = NULL; Sint i; - if ((i = erts_list_length(A)) < 0) { - BIF_ERROR(p, BADARG); + list = A; + + if (is_nil(list)) { + BIF_RET(B); } - if (i == 0) { - BIF_RET(B); - } else if (is_nil(B)) { - BIF_RET(A); + + if (is_not_list(list)) { + BIF_ERROR(p, BADARG); } - need = 2*i; - hp = HAlloc(p, need); - list = A; + /* optimistic append on heap first */ + + if ((i = HeapWordsLeft(p) / 2) < 4) { + goto list_tail; + } + + hp = HEAP_TOP(p); copy = last = CONS(hp, CAR(list_val(list)), make_list(hp+2)); list = CDR(list_val(list)); - hp += 2; + hp += 2; + i -= 2; /* don't use the last 2 words (extra i--;) */ + + while(i-- && is_list(list)) { + Eterm* listp = list_val(list); + last = CONS(hp, CAR(listp), make_list(hp+2)); + list = CDR(listp); + hp += 2; + } + + /* A is proper and B is NIL return A as-is, don't update HTOP */ + + if (is_nil(list) && is_nil(B)) { + BIF_RET(A); + } + + if (is_nil(list)) { + HEAP_TOP(p) = hp; + CDR(list_val(last)) = B; + BIF_RET(copy); + } + +list_tail: + + if ((i = erts_list_length(list)) < 0) { + BIF_ERROR(p, BADARG); + } + + /* remaining list was proper and B is NIL */ + if (is_nil(B)) { + BIF_RET(A); + } + + if (hp) { + /* Note: fall through case, already written + * on the heap. + * The last 2 words of the heap is not written yet + */ + Eterm *hp_save = hp; + ASSERT(i != 0); + HEAP_TOP(p) = hp + 2; + if (i == 1) { + hp[0] = CAR(list_val(list)); + hp[1] = B; + BIF_RET(copy); + } + hp = HAlloc(p, 2*(i - 1)); + last = CONS(hp_save, CAR(list_val(list)), make_list(hp)); + } else { + hp = HAlloc(p, 2*i); + copy = last = CONS(hp, CAR(list_val(list)), make_list(hp+2)); + hp += 2; + } + + list = CDR(list_val(list)); i--; + + ASSERT(i > -1); while(i--) { - Eterm* listp = list_val(list); - last = CONS(hp, CAR(listp), make_list(hp+2)); - list = CDR(listp); - hp += 2; + Eterm* listp = list_val(list); + last = CONS(hp, CAR(listp), make_list(hp+2)); + list = CDR(listp); + hp += 2; } + CDR(list_val(last)) = B; BIF_RET(copy); } |