C#中点向下舍入到零 [英] C# midpointrounding down to zero

问题描述

我知道MidpointRounding.AwayFromZero和MidpointRounding.ToEven，但是我想我希望两者之间有一些联系.它是用于促销模块的，因此折扣值必须取整(如果值是.5).

I know about MidpointRounding.AwayFromZero and MidpointRounding.ToEven, but I think I want something inbetween. It is for a promotions module, so discounted prices must round down if the value is .5.

例如，我想要:

£1.244 to round to £1.24
£1.245 to round to £1.24
£1.246 to round to £1.25

据我了解，.AwayFromZero将中间值四舍五入为1.25英镑，.ToEven将正确舍入为1.24英镑，但是1.335英镑将被四舍五入为1.34英镑，而不是我想要的1.33英镑.

As I understand it, .AwayFromZero would round the middle value to £1.25 and .ToEven would round correctly to £1.24, but £1.335 would be rounded to £1.34, rather than £1.33 which is what I want.

有人知道如何做到这一点吗?

Does anyone know how to accomplish this?

谢谢乔恩

推荐答案

有很多未指定的行为.让我们保持安全并明确地进行舍入，忽略负数，因为这与金钱有关:

There is a lot of unspecified behavior. Let's keep it safe and do the rounding explicitly, ignoring negatives since this is about money:

    public static decimal Promotion(decimal value) {
        decimal unround = decimal.Floor(value * 100m);
        decimal fraction = value * 100m - unround;
        if (fraction <= 0.5m) return unround / 100m;
        else return (unround + 1m) / 100m;
    }

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