如何优化for循环 [英] how to optimize a for loop
问题描述
我有这个循环（所有变量都是指针）：
for（foo = bar; foo baz; foo--）
*（foo + 1）= * foo;
如何优化指针交换以便它使用 - 和++或一元
+ - 而不是+1（如果可能的话 - 我不是'我想要比代码更多#defines
）？
IOCCC获奖者可以真正帮助我：P
I have this loop (all variables are pointers):
for (foo = bar; foo baz; foo--)
*(foo+1) = *foo;
How do I optimize the pointer swap so that it uses -- and ++ or unary
+- instead of +1 (if possible - I don''t want to have more #defines
than code)?
IOCCC winners can really help me with this :P
推荐答案
10月30日下午6:14，andreyvul< andrey .... @ gmail.comwrote：
On Oct 30, 6:14 pm, andreyvul <andrey....@gmail.comwrote:
我有这个循环（所有变量都是指针）：
for（foo = bar; foo baz; foo--）
*（foo + 1）= * foo ;
如何优化指针交换以便它使用 - 和++或一元
+ - 而不是+1（如果可能的话 - 我不会想要比代码更多#defines
）？
IOCCC获奖者可以真正帮助我：P
I have this loop (all variables are pointers):
for (foo = bar; foo baz; foo--)
*(foo+1) = *foo;
How do I optimize the pointer swap so that it uses -- and ++ or unary
+- instead of +1 (if possible - I don''t want to have more #defines
than code)?
IOCCC winners can really help me with this :P
memmove（foo + 1，foo，len）;
注意memcpy（）是这里不允许。
memmove(foo+1, foo, len);
Note that memcpy() is not allowed here.
10月30日晚上9点26分，user923005< dcor ... @ connx.comwrote：
On Oct 30, 9:26 pm, user923005 <dcor...@connx.comwrote:
10月30日下午6:14，andreyvul< andrey .... @ gmail.com写道：
On Oct 30, 6:14 pm, andreyvul <andrey....@gmail.comwrote:
我有这个循环（所有变量都是指针）：
for（foo = bar; foo baz; foo--）
*（foo + 1）= * foo;
如何优化指针交换以便它使用 - 和++或一元
+ - 而不是+1（如果可能的话 - 我不想比代码更多#defines
）？
IOCCC获奖者可以真的帮助我：P
I have this loop (all variables are pointers):
for (foo = bar; foo baz; foo--)
*(foo+1) = *foo;
How do I optimize the pointer swap so that it uses -- and ++ or unary
+- instead of +1 (if possible - I don''t want to have more #defines
than code)?
IOCCC winners can really help me with this :P
memmove（foo + 1，foo，len）;
请注意memcpy（ ）这里不允许。
memmove(foo+1, foo, len);
Note that memcpy() is not allowed here.
打破我的就地合并，对不起。与此相同的结果：
for（foo = bar + 1; foo baz;）
*（foo）= *（ - foo）;
虽然我猜测'两个班轮中的memmove是如何工作的。
有没有办法优化插入排序'的内循环是我
的意思。
完整的排序代码（t是一个值变量）：
/ * ...分而治之...... * /
for（;（start< = mid）&&（mid + 1< = end）; start ++）{
if（* start< *（mid +） 1））//排序（当前元素属于第一个
一半）
继续;
else {/ * true inplace merge需要insersion-排序类似
*方法，因为下半部分的值被插入到
*当前元素* /
//复制第一个下半场中的元素t
t = *（mid + 1）;
//将上半场向右移动（这是我试图
优化）
for（shift = mid; shift> = start; shift--）
*（sh ift + 1）= * shift;
//复制t开始
* start = t;
mid ++;
}
}
Breaks my in-place mergesort, sorry. Same result as with this:
for (foo = bar + 1; foo baz;)
*(foo) = *(--foo);
Though I''m guessing that''s how memmove works in a two-liner.
Is there a way to optimize insertion sort''s inner loop is what I
meant.
full sort code (t is a value variable):
/* ... divide and conquer ... */
for (;(start <= mid) && (mid + 1 <= end); start++) {
if (*start < *(mid + 1)) //sorted (current element belongs in 1st
half)
continue;
else { /* true inplace merge requires insersion-sort-like
* methods because a value from the second half is inserted to
* the current element */
//copy the first element in the second half to t
t = *(mid + 1);
//shift first half to the right (this is what I was trying to
optimize)
for (shift = mid; shift >= start; shift--)
*(shift + 1) = *shift;
//copy t to start
*start = t;
mid++;
}
}
andreyvul< an ******** @ gmail.comwrites：
andreyvul <an********@gmail.comwrites:
我有这个循环（所有变量都是指针）：
for（foo = bar; foo baz; foo--）
*（foo + 1）= * foo;
如何优化指针交换以便它使用 - 和++或一元
+ - 而不是+1（如果可能的话 - 我不想比代码更多#defines
）？
IOCCC获奖者可以真的帮助我：P
I have this loop (all variables are pointers):
for (foo = bar; foo baz; foo--)
*(foo+1) = *foo;
How do I optimize the pointer swap so that it uses -- and ++ or unary
+- instead of +1 (if possible - I don''t want to have more #defines
than code)?
IOCCC winners can really help me with this :P
是什么让你认为替换+ 1用++表示是优化吗？
-
Keith Thompson（The_Other_Keith） ks * **@mib.org < http://www.ghoti.net/~kst>
圣地亚哥超级计算机中心< *< http://users.sdsc。 edu / ~kst>
我们必须做点什么。这是事情。因此，我们必须这样做。
- Antony Jay和Jonathan Lynn，是部长
What makes you think that replacing "+1" with "++" is an optimization?
--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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