Numerical Methods with MATLAB(NMM1[1].5计算方法工具箱).

/* File: binSearch.c * * C source code for MEX version of binary search routine * G.W. Recktenwald, 5 Jan 1998 */ #include <math.h> #include "mex.h" /* Input Arguments */ #define X_IN prhs[0] #define XHAT_IN prhs[1] /* Output Arguments */ #define INDEX_OUT plhs[0] /* -------- prototypes for functions defined in this file */ unsigned int binSearch(double x[], unsigned int n, double xhat); /* -------- Begin mexFunction(), the mex gateway to MATLAB -----------*/ void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[] ) { double *i,*x,*xhat; unsigned int n; int rows, cols; /* Check for proper number of arguments */ if (nrhs != 2) { mexErrMsgTxt("binSearch requires two input arguments."); } else if (nlhs > 1) { mexErrMsgTxt("binSearch requires one output argument."); } /* Create a matrix for the return argument */ INDEX_OUT = mxCreateDoubleMatrix(1, 1, mxREAL); /* Assign pointers to the input and output parameters */ i = mxGetPr(INDEX_OUT); x = mxGetPr(X_IN); xhat = mxGetPr(XHAT_IN); rows = mxGetM(X_IN); /* Get number of rows in input matrix */ cols = mxGetN(X_IN); /* Get number of columns */ n = rows * cols; /* Total number of elements */ /* The binSearch does the work and returns an unsigned int, * which must be cast to double before assigning to i. * Note that binSearch() returns the zero-offset index. * Add one to that result to get proper MATLAB index, * which is unit offset */ *i = (double)(1+binSearch(x,n,*xhat)); return; } /* ------------------ binSearch() --------------------------- */ /* * Binary search to find index i such that x[i] <= xhat <= x[i+1] * * Input: x[] = (double) vector of monotonic data * n = (unsigned int) length of x[] * xhat = test value * * Return: i = index in x vector such that x[i]<= xhat <= x[i+1] * * Note: This C function returns the index in the zero-offset * vector x. Add one to the result to obtain the correct * MATLAB index, which is unit-offset. */ unsigned int binSearch(double x[], unsigned int n, double xhat) { unsigned int ia,ib,im; ia = 0; ib = n-1; /* Last element is n-1 for zero-offset vector */ while (ib-ia>1) { im = (ia+ib) >> 1; /* Right shift by 1 is efficient integer divide by 2 */ if (x[im] < xhat) { ia = im; /* Replace lower bracket */ } else { ib = im; /* Replace upper bracket */ } } return ia; /* While loop terminates when ia is desired index */ }