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Optimize Array#rotate!(n) for n = 1 and n = -1

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For the most common cases of `rotate!` one place to the right or to the
left, instead of doing some reversals of the array we just keep a single
value in a temporary value, use memmove and then put the temporary
value where it should be.
This commit is contained in:
Ary Borenszweig 2019-11-29 17:59:47 -03:00 • committed by Nobuyoshi Nakada
parent a0d1fd16d1
commit e5c441a4a2
Notes: git 2019-12-29 13:13:05 +09:00
1 changed files with 15 additions and 5 deletions
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20
array.c
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@ -2618,10 +2618,20 @@ rotate_count(long cnt, long len)
static void
ary_rotate_ptr(VALUE *ptr, long len, long cnt)
{
--len;
if (cnt < len) ary_reverse(ptr + cnt, ptr + len);
if (--cnt > 0) ary_reverse(ptr, ptr + cnt);
if (len > 0) ary_reverse(ptr, ptr + len);
if (cnt == 1) {
VALUE tmp = *ptr;
memmove(ptr, ptr + 1, sizeof(VALUE)*(len - 1));
*(ptr + len - 1) = tmp;
} else if (cnt == len - 1) {
VALUE tmp = *(ptr + len - 1);
memmove(ptr + 1, ptr, sizeof(VALUE)*(len - 1));
*ptr = tmp;
} else {
--len;
if (cnt < len) ary_reverse(ptr + cnt, ptr + len);
if (--cnt > 0) ary_reverse(ptr, ptr + cnt);
if (len > 0) ary_reverse(ptr, ptr + len);
}
}
VALUE
@ -2631,7 +2641,7 @@ rb_ary_rotate(VALUE ary, long cnt)
if (cnt != 0) {
long len = RARRAY_LEN(ary);
if (len > 0 && (cnt = rotate_count(cnt, len)) > 0) {
if (len > 1 && (cnt = rotate_count(cnt, len)) > 0) {
RARRAY_PTR_USE_TRANSIENT(ary, ptr, ary_rotate_ptr(ptr, len, cnt));
return ary;
}