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array.c : speedup Array#unshift by using space in shared array

- when array owns its shared array (ARY_SHARED_NUM == 1),
  and there is enough space then try unshift values directly into shared
  array
- when resulting array is big (~>64 items) then make it shared
  with enough room for future #unshifts, and then insert into shared array
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funny-falcon committed Sep 2, 2012
1 parent 283253c commit 6f67f1da1e5e60c0c7a0ab65e430fddacea7226e
Showing with 55 additions and 9 deletions.
  1. +55 −9 array.c
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64 array.c
@@ -970,6 +970,55 @@ rb_ary_shift_m(int argc, VALUE *argv, VALUE ary)
return result;
}
+static void
+ary_ensure_room_for_unshift(VALUE ary, int argc)
+{
+ long len = RARRAY_LEN(ary);
+ long new_len = len + argc;
+ long capa;
+ VALUE *head, *sharedp;
+
+ if (ARY_SHARED_P(ary)) {
+ VALUE shared = ARY_SHARED(ary);
+ capa = RARRAY_LEN(shared);
+ if (ARY_SHARED_NUM(shared) == 1 && capa > new_len) {
+ head = RARRAY_PTR(ary);
+ sharedp = RARRAY_PTR(shared);
+ goto makeroom_if_need;
+ }
+ }
+
+ rb_ary_modify(ary);
+ capa = ARY_CAPA(ary);
+ if (capa - (capa >> 6) <= new_len) {
+ ary_double_capa(ary, new_len);
+ }
+
+ /* use shared array for big "queues" */
+ if (new_len > ARY_DEFAULT_SIZE * 4) {
+ /* make a room for unshifted items */
+ capa = ARY_CAPA(ary);
+ ary_make_shared(ary);
+
+ head = sharedp = RARRAY_PTR(ary);
+ goto makeroom;
+makeroom_if_need:
+ if (head - sharedp < argc) {
+ long room;
+makeroom:
+ room = capa - new_len;
+ room -= room >> 4;
+ MEMMOVE(sharedp + argc + room, head, VALUE, len);
+ head = sharedp + argc + room;
+ }
+ ARY_SET_PTR(ary, head - argc);
+ }
+ else {
+ /* sliding items */
+ MEMMOVE(RARRAY_PTR(ary) + argc, RARRAY_PTR(ary), VALUE, len);
+ }
+}
+
/*
* call-seq:
* ary.unshift(obj, ...) -> ary
@@ -985,19 +1034,16 @@ rb_ary_shift_m(int argc, VALUE *argv, VALUE ary)
static VALUE
rb_ary_unshift_m(int argc, VALUE *argv, VALUE ary)
{
- long len;
+ long len = RARRAY_LEN(ary);
- rb_ary_modify(ary);
- if (argc == 0) return ary;
- if (ARY_CAPA(ary) <= (len = RARRAY_LEN(ary)) + argc) {
- ary_double_capa(ary, len + argc);
+ if (argc == 0) {
+ rb_ary_modify_check(ary);
+ return ary;
}
- /* sliding items */
- MEMMOVE(RARRAY_PTR(ary) + argc, RARRAY_PTR(ary), VALUE, len);
+ ary_ensure_room_for_unshift(ary, argc);
MEMCPY(RARRAY_PTR(ary), argv, VALUE, argc);
- ARY_INCREASE_LEN(ary, argc);
-
+ ARY_SET_LEN(ary, len + argc);
return ary;
}

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