对于 C++ 整数，1 除以 2 是否可靠地等于 0，3/2 = 1、5/2 = 2 等等？
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With c++ integers, does 1 divided by 2 reliably equal 0, and 3/2 = 1, 5/2 = 2 etc.?
提问by mosi
There are two vectors of differing, yet related sizes. The larger is (2 * RESOLUTION) + INDEX_OFFSET(e.g. 2050) and the smaller is simply RESOLUTION(e.g. 1024). I believe it safe enough to assume that uint16_tcan be used to contain the vector index.
有两个大小不同但相关的向量。较大的是(2 * RESOLUTION) + INDEX_OFFSET（例如2050），较小的是RESOLUTION（例如1024）。我相信它足够安全，uint16_t可以用来包含向量索引。
Iteration through the larger vector is performed by incrementing resultIndexby 2. During each iteration, an assignment is made to the smaller vector at the index (resultIndex - INDEX_OFFSET) / 2.
对较大向量的迭代通过增加resultIndex2来执行。在每次迭代期间，对索引处的较小向量进行分配(resultIndex - INDEX_OFFSET) / 2。
Essentially, the code relies on the assumption that, whether INDEX_OFFSETis odd or even, the above division by 2 will always round down, regardless of architecture. For example, if resultIndexis 0 or 1, then 0 is expected, if is it 2 or 3 then 1 is expected, and so on. Is this a safe assumption, within the parameters above?
本质上，代码依赖于这样的假设：无论INDEX_OFFSET是奇数还是偶数，上述除以 2 的结果总是向下取整，无论架构如何。例如，如果resultIndex是 0 或 1，则预期为 0，如果是 2 或 3，则预期为 1，依此类推。在上述参数范围内，这是一个安全的假设吗？
N.B. I acknowledge the existence of 'Dividing integer types - Are results predictable?'but it does not seem to be an exact match.
注意，我承认存在“划分整数类型 - 结果是否可预测？” 但它似乎并不完全匹配。
回答by Lightness Races in Orbit
Yes; this is guaranteed by the language:
是的; 这是由语言保证的：
[C++11: 5.6/4]:The binary/operator yields the quotient, and the binary%operator yields the remainder from the division of the first expression by the second. If the second operand of/or%is zero the behavior is undefined. For integral operands the/operator yields the algebraic quotient with any fractional part discarded;if the quotienta/bis representable in the type of the result,(a/b)*b + a%bis equal toa.
[C++11: 5.6/4]:二元/运算符产生商，二元%运算符产生第一个表达式除以第二个表达式的余数。如果/or的第二个操作数%为零，则行为未定义。对于整数操作数，/运算符产生代数商，其中任何小数部分都被丢弃；如果商a/b可在结果的类型中表示，(a/b)*b + a%b则等于a。
In 3/2, both 3and 2are integral operands; the algebraic quotient of this operation is 1.5, and when you discard the fractional part .5, you get 1. This holds for your other examples and, well, all other examples.
在 中3/2，3和2都是整数操作数；此运算的代数商为1.5，当您丢弃小数部分时.5，您会得到1。这适用于您的其他示例以及所有其他示例。
