在默认环境下，vdsp认为double和float这两种范例是一样的，因此我们较量long double和float。
1.1 范例暗示
下面是两种范例的数据暗示：
| float | long double | |
| 字节数 | 4 | 8 |
| 标记位 | 1 | 1 |
| 指数位数 | 8 | 11 |
| 尾数位数 | 23 | 52 |
| 最小值 | 1.1754943508222875E-38F | 2.2250738585072014E-308L |
| 最大值 | 3.4028234663852886E+38F | 1.797693134862315708E+308L |
| 判别率 | 1.1920928955078125E-07F | 2.2204460492503131E-16L |
1.2 正常环境下的运算效率
下表给出两种范例下做运算的效率较量，选择High performance
| float | long double | |
| 加减运算 | 132 cycle | 166 cycle |
| 乘法运算 | 92 cycle | 179 cycle |
| 除法运算 | 240 cycle | 1506 cycle |
狂汗，这个long double做除法也太狠了点！
下表给出两种范例下做运算的效率较量，选择Strict IEEE：
| Float | long double | |
| 加减运算 | 310 cycle | 381 cycle |
| 乘法运算 | 274 cycle | 585 cycle |
| 除法运算 | 497 cycle | 1063 cycle |
这里有一个值显得很奇怪，在选择了Strict IEEE选项之后，long double举办除法运算反而变快了！
在vdsp的文档里这样表明这两种差异的选项：
The -fast-fp (fast floating point) switch directs the compiler to link with the high-speed floating-point emulation library. This library relaxes some of the IEEE floating-point standard’s rules for checking inputs against not-a-number (NaN) and denormalized numbers to improve performance. This switch is enabled by default.
The -ieee-fp (slower floating point) switch directs the compiler to link with the fully-compliant floating-point emulation library. This library obeys all of the IEEE floating-point standard’s rules, and incurs a performance penalty when compared with the default floating-point emulation library.
照说利用Strict IEEE选项之后应该所有的计较都变慢，但long double的浮点除法好像是个破例！
