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再给你看看 Intel 的说法:
前面介绍了x87 FPU有8个80位扩展双精度的寄存器用于数据计算。支持的数据编码格式,除了整形,浮点有三种:单精度float,双精度double,和扩展双精度 long double,接下来描述这三种的用途
As a general rule, values should be stored in memory in double-precision format. This format provides sufficient range and precision to return correct results with a minimum of programmer attention.
The single-precision format is useful for debugging algorithms, because rounding problems will manifest themselves more quickly in this format.
The double extended-precision format is normally reserved for holding intermediate results in the x87 FPU registers and constants. Its extra length is designed to shield final results from the effects of rounding and overflow/underflow in intermediate calculations. However, when an application requires the maximum range and precision of the x87 FPU (for data storage, computations, and results), values can be stored in memory in double extended-precision format.
所以你想让x87 FPU进行一次单精度舍入的乘法运算是不可能的,x86平台上只有软件模拟才能做到。
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