vl_binsearch.c

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/*
Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
All rights reserved.

This file is part of the VLFeat library and is made available under
the terms of the BSD license (see the COPYING file).
*/

#include <mexutils.h>

void
mexFunction(int nout, mxArray *out[],
            int nin, const mxArray *in[])
{
  enum { IN_B=0, IN_X, IN_END } ;
  enum { OUT_IDX=0 } ;
  vl_size numElementsX, numElementsB ;
  const double *X, *B ;
  double *IDX ;

  if (nout > 1) {
    vlmxError(vlmxErrTooManyOutputArguments, NULL) ;
  }
  if (nin != 2) {
    vlmxError(vlmxErrInvalidArgument,
              "Incorrect number of arguments.") ;
  }
  if (! vlmxIsPlain (IN(B)) ||
      ! vlmxIsPlain (IN(X)) ) {
    vlmxError(vlmxErrInvalidArgument,
              "All arguments must be plain arrays.") ;
  }

  numElementsX = mxGetNumberOfElements(IN(X)) ;
  numElementsB = mxGetNumberOfElements(IN(B)) ;

  {
    mwSize const * dimensions = mxGetDimensions(IN(X)) ;
    vl_size numDimensions = mxGetNumberOfDimensions(IN(X)) ;
    OUT(IDX) = mxCreateNumericArray (numDimensions, dimensions, mxDOUBLE_CLASS, mxREAL) ;
  }

  /* if B is empty it defines only [-inf, +inf) */
  if (numElementsB == 0) return ;

  IDX = mxGetPr(OUT(IDX)) ;
  X = mxGetPr(IN(X)) ;
  B = mxGetPr(IN(B)) ;

  {
    vl_uindex i ;
    for (i = 0 ; i < numElementsX ; ++i) {
      double x = X[i] ;
      vl_uindex blower = 0 ;
      vl_uindex bupper = numElementsB - 1 ;
      vl_uindex bsplit ;

      if (x < B[0]) {
        IDX [i] = 0 ;
        continue ;
      }

      if (x >= B[numElementsB - 1]) {
        IDX [i] = numElementsB ;
        continue ;
      }

      while (blower + 1 < bupper) {
        bsplit = (bupper + blower) / 2 ;
        if (x < B[bsplit]) bupper = bsplit ;
        else blower = bsplit ;
      }
      IDX [i] = blower + 1 ;
    }
  }
}