管理 C++ 单精度和双精度混合计算的规则是什么? [英] What are the rules governing C++ single and double precision mixed calculations?

问题描述

例如，这些变量:

result (double)
a (double)
b (float)
c (float)
d (double)

一个简单的计算:

result = a * (b + c) * d

类型转换的方式和时间以及如何确定每次计算的执行精度?

How and when are the types converted and how do I figure out what precision each calculation is performed at?

推荐答案

所有操作都是在相同类型的对象上完成的(假设是正常的算术运算).

All operations are done on objects of the same type (assuming normal arithmetic operations).

如果您编写的程序使用不同的类型，那么编译器会自动升级 ONE 参数，使它们都相同.

If you write a program that uses different types then the compiler will auto upgrade ONE parameter so that they are both the same.

在这种情况下，浮点数将升级为双精度数:

In this situations floats will be upgraded to doubles:

result      = a * (b + c) * d

float  tmp1 = b + c;            // Plus operation done on floats.
                                // So the result is a float

double tmp2 = a * (double)tmp1; // Multiplication done on double (as `a` is double)
                                // so tmp1 will be up converted to a double.

double tmp3 = tmp2 * d;         // Multiplication done on doubles.
                                // So result is a double

result      = tmp3;             // No conversion as tmp3 is same type as result.

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