comparison toolboxes/distance_learning/mlr/util/binarysearch.c @ 0:e9a9cd732c1e tip

first hg version after svn

+/* CREATED:2010-01-17 08:12:57 by Brian McFee <[e-mail]> */
+/* binarysearch.c
+ *
+ *  binary search
+ *
+ * Compile: 
+ *  mex binarysearch.c
+ */
+
+#include "mex.h"
+
+
+void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
+{
+    /* Declare variables */
+    int nQuery, nData;          /* number of elements */
+    double *pQuery, *pData;     /* input arrays */
+    double *positions;          /* output array(s) */
+
+    int i;
+
+    if (nrhs != 2) {
+        mexErrMsgTxt("Two input arguments are required.");
+    }
+    if (nlhs > 1) {
+        mexErrMsgTxt("Too many output arguments.");
+    }
+
+    if (!(mxIsDouble(prhs[0])) || !(mxIsDouble(prhs[1]))) {
+        mexErrMsgTxt("Input arrays must be of type double.");
+    }
+
+    nQuery      = mxGetNumberOfElements(prhs[0]);
+    nData       = mxGetNumberOfElements(prhs[1]);
+    pQuery      = (double *)mxGetPr(prhs[0]);
+    pData       = (double *)mxGetPr(prhs[1]);
+    
+    plhs[0]     = mxCreateDoubleMatrix(1, nQuery, mxREAL);
+    positions   = mxGetPr(plhs[0]);
+
+    /* Now for the meat */
+
+    for (i = 0; i < nQuery; i++) {
+        positions[i] = 0;
+        positions[i] = binarysearch(pQuery[i], pData, nData);
+    }
+
+    mxSetN(plhs[0], nQuery);
+}
+
+int binarysearch(double q, double *data, int n) {
+    int l = 0;
+    int u = n-1;
+    int pivot;
+
+    while (l < u) {
+        pivot = l + (u - l) / 2;
+
+        if (q > data[pivot]) {
+            u = pivot - 1;
+        } else {
+            l = pivot + 1;
+        }
+    }
+
+    /* Break ties to the right */
+    if (l == n || q > data[l]) {
+        return l;
+    } else {
+        return l + 1;
+    }
+
+}