问题描述
当尝试运行下面的示例代码(类似于查找表)时，它总是生成以下错误消息:函数'out'的纯定义以维度0的方式来无限制地调用函数'color'"
When trying to run the sample code below (similar to a look up table), it always generates the following error message: "The pure definition of Function 'out' calls function 'color' in an unbounded way in dimension 0".
RDom r(0, 10, 0, 10);
Func label, color, out;
Var x,y,c;
label(x,y) = 0;
label(r.x,r.y) = 1;
color(c) = 0;
color(label(r.x,r.y)) = 255;
out(x,y) = color(label(x,y));
out.realize(10,10);
在调用实现之前，我试图像下面这样静态设置边界，但没有成功.
Before calling realize, I have tried to statically set bound, like below, without success.
color.bound(c,0,10);
label.bound(x,0,10).bound(y,0,10);
out.bound(x,0,10).bound(y,0,10);
我也看了直方图示例，但是它们有些不同.
I also looked at the histogram examples, but they are a bit different.
这是Halide中的某种限制吗?
Is this some kind of restrictions in Halide?
推荐答案
卤化物可通过分析作为参数传递给Func的值的范围来防止任何越界访问(并决定要计算的内容).如果这些值是无界的，则无法做到这一点.使它们有界的方法是使用钳位:
Halide prevents any out of bounds access (and decides what to compute) by analyzing the range of the values you pass as arguments to a Func. If those values are unbounded, it can't do that. The way to make them bounded is with clamp:
out(x, y) = color(clamp(label(x, y), 0, 9));
在这种情况下，其不受限制的原因是标签具有更新定义，这使分析放弃了.如果您改写这样的标签:
In this case, the reason it's unbounded is that label has an update definition, which makes the analysis give up. If you wrote label like this instead:
label(x, y) = select(x >= 0 && x < 10 && y >= 0 && y < 10, 1, 0);
那么您就不需要夹子了.
Then you wouldn't need the clamp.
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