问题描述
是
if(!test)
快于
if(test==-1)
我可以生产装配，但生产的装配太多，我不能找到我之后的细节。我希望有人只知道答案。我猜想他们是一样的，除非大多数CPU架构有某种比较零的捷径。
I can produce assembly but there is too much assembly produced and I can never locate the particulars I'm after. I was hoping someone just knows the answer. I would guess they are the same unless most CPU architectures have some sort of "compare to zero" short cut.
感谢任何帮助。
推荐答案
通常情况下，是的。在典型的处理器测试零，或测试符号（负/正）是简单的条件代码检查。这意味着可以重新排序指令以省略测试指令。在伪汇编中，考虑这样：
Typically, yes. In typical processors testing against zero, or testing sign (negative/positive) are simple condition code checks. This means that instructions can be re-ordered to omit a test instruction. In pseudo assembly, consider this:
Loop:
LOADCC r1, test // load test into register 1, and set condition codes
BCZS Loop // If zero was set, go to Loop
测试1：
Loop:
LOAD r1, test // load test into register 1
SUBT r1, 1 // Subtract Test instruction, with destination suppressed
BCNE Loop // If not equal to 1, go to Loop
现在对于通常的优化前免责声明：您的程序太慢了？不进行优化，对其进行配置。
Now for the usual pre-optimization disclaimer: Is your program too slow? Don't optimize, profile it.
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