MATLAB Mex函数可以接受单打和双打吗? [英] Can a MATLAB Mex function accept both single and doubles?

问题描述

我有一个接受双矩阵作为输入的mex函数，但我刚刚意识到该函数所使用的代码也可以具有单精度矩阵.是否可以允许该函数接受其中任何一个?

I have a mex function that accepts double matrices as the input, but I just realized that the code this function is used for, can have single precision matrices as well. Is it possible to allow the function to accept either?

否则，解决此问题的另一种方法是什么?

Or if not, what is an alternative way to fix this issue?

推荐答案

简单的解决方案是将MATLAB中的输入转换为一致的类型(大概是double)，但是如果您想让MEX函数处理多种类型的话，这是一种方法.

The simple solution would be to convert the inputs in MATLAB to a consistent type (presumably double), but if you would like to have your MEX function handle multiple types, here is one way.

使用 mxIsSingle 和 mxIsDouble (或 ，而无需任何数据转换.

Check the input type with mxIsSingle and mxIsDouble (or mxIsClass) and handle it accordingly. You might have an ifstatement in mexFunction that sets up the inputs and outputs and then calls a template function. See the example below, which thresholds all the values in an array using the C++ standard library function template std::min<T> without requiring any data conversion.

flexibleFunction.cpp

#include "mex.h"
#include <algorithm> // std::min

template <typename T>
void threshArrayLT(T *out, const T *arr, mwSize n, T c)
{  // you allocate out
    for (mwSize i = 0; i < n; ++i)
        out[i] = std::min<T>(arr[i], c);
}

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
    if (nlhs > 1 || nrhs != 2)
        mexErrMsgTxt("Syntax:\n\tH = flexibleFunction(arr,c)");

    if (!mxIsDouble(prhs[0]) && !mxIsSingle(prhs[0]))
        mexErrMsgTxt("Array must be double or single.");

    if ((mxIsDouble(prhs[0]) && !mxIsDouble(prhs[1])) || 
            (mxIsSingle(prhs[0]) && !mxIsSingle(prhs[1])))
        mexErrMsgTxt("Arguments must have same type.");

    const mwSize* dims = mxGetDimensions(prhs[0]);
    int ndims = static_cast<int>(mxGetNumberOfDimensions(prhs[0]));
    size_t numel = mxGetNumberOfElements(prhs[0]);

    if (mxIsDouble(prhs[0])) {
        double *arr = mxGetPr(prhs[0]);
        double c = mxGetScalar(prhs[1]);
        plhs[0] = mxCreateNumericArray(ndims,dims,mxDOUBLE_CLASS,mxREAL);
        threshArrayLT(mxGetPr(plhs[0]),arr,numel,c);
        // In reality, if it's this simple, use std::transform with lambda or bind:
        //std::transform(arr, arr+numel, mxGetPr(plhs[0]), 
        //    [&](double s){ return std::min(s,c); });
    } else if (mxIsSingle(prhs[0])) {
        float *arr = (float*)mxGetData(prhs[0]);
        float c = static_cast<float>(mxGetScalar(prhs[1]));
        plhs[0] = mxCreateNumericArray(ndims,dims,mxSINGLE_CLASS,mxREAL);
        threshArrayLT((float*)mxGetData(plhs[0]),arr,numel,c);
    }
}

您还可以在C ++中使用函数重载(相同的名称，不同的参数类型).

You can also use function overloading in C++ (same name, different argument types).

示例

>> v = rand(1,8); c = 0.5;
>> whos v c
  Name      Size            Bytes  Class     Attributes

  c         1x1                 8  double              
  v         1x8                64  double           


>> flexibleFunction(v,c)
ans =
    0.2760    0.5000    0.5000    0.1626    0.1190    0.4984    0.5000    0.3404
>> flexibleFunction(single(v),single(c))
ans =
    0.2760    0.5000    0.5000    0.1626    0.1190    0.4984    0.5000    0.3404

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