Objective中的非规格化浮点
Stack Overflow的相关性问题/答案为什么将0.1f更改为0会使性能下降10倍？ 为Objective-C？ 如果有任何相关性，这应如何改变我的编码习惯？ 有什么方法可以关闭Mac OS X上的非规格化浮点？
这似乎与iOS完全无关。 那是对的吗？
正如我在回答你的评论时说的那样：
它不仅仅是一个CPU而是一个语言问题，所以它可能与x86上的Objective-C有关。 （iPhone的ARMv7似乎不支持非规范化浮点数，至少使用默认的运行时/构建设置）
更新
我刚测试过。 在x86上的Mac OS X上观察到速度下降，在ARMv7上的iOS上它不是（默认构建设置）。
而且可以预料，在iOS模拟器（在x86上）运行的非规范化浮点数会再次出现。
有趣的是， FLT_MIN和DBL_MIN分别被定义为最小的非非规格化数字（在iOS，Mac OS X和Linux上）。 奇怪的事情发生使用
DBL_MIN/2.0
在你的代码中; 编译器很高兴地设置一个非规格化的常量，但只要（arm）CPU触及它，它就被设置为零：
double test = DBL_MIN/2.0;
printf("test == 0.0 %dn",test==0.0);
printf("DBL_MIN/2 == 0.0 %dn",DBL_MIN/2.0==0.0);
输出：
test == 0.0 1 // computer says YES
DBL_MIN/2 == 0.0 0 // compiler says NO
因此，快速运行时检查是否支持非规范化可以是：
#define SUPPORT_DENORMALIZATION ({volatile double t=DBL_MIN/2.0;t!=0.0;})
（“即使没有适用于任何目的的暗示保证”也是如此）
这就是ARM在刷新到零模式时所说的：http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204h/Bcfheche.html
更新<< 1
这是您在ARMv7上禁用刷新到零模式的方式：
int x;
asm(
"vmrs %[result],FPSCR rn"
"bic %[result],%[result],#16777216 rn"
"vmsr FPSCR,%[result]"
:[result] "=r" (x) : :
);
printf("ARM FPSCR: %08xn",x);
以下惊人的结果。
您可以清楚地看到反规范化的成本为零。 （对于iPad 2.在iPhone 4上，它的成本只有10％的小幅下降。）
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