diff --git a/c/coreslam_sisd.c b/c/coreslam_sisd.c
new file mode 100644
index 0000000..81c8b98
--- /dev/null
+++ b/c/coreslam_sisd.c
@@ -0,0 +1,70 @@
+/*
+coreslam_sisd.c SISD default for CoreSLAM when SSE not available. 
+
+Adapted from code in CoreSLAM.c downloaded from openslam.org on 01 January 2014.  
+
+Copyright (C) 2014 Simon D. Levy
+
+This code is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as 
+published by the Free Software Foundation, either version 3 of the 
+License, or (at your option) any later version.
+
+This code is distributed in the hope that it will be useful,     
+but WITHOUT ANY WARRANTY without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License 
+along with this code.  If not, see <http:#www.gnu.org/licenses/>.
+
+*/
+
+
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "coreslam.h"
+#include "coreslam_internals.h"
+
+int 
+distance_scan_to_map(
+    map_t *  map,
+    scan_t * scan,
+    position_t position)
+{    
+    /* Pre-compute sine and cosine of angle for rotation */
+    double position_theta_radians = radians(position.theta_degrees);
+    double costheta = cos(position_theta_radians) * map->scale_pixels_per_mm;
+    double sintheta = sin(position_theta_radians) * map->scale_pixels_per_mm;
+    
+    /* Pre-compute pixel offset for translation */
+    double pos_x_pix = position.x_mm * map->scale_pixels_per_mm;
+    double pos_y_pix = position.y_mm * map->scale_pixels_per_mm;
+
+    int64_t sum = 0; /* sum of map values at those points */
+    int npoints = 0; /* number of points where scan matches map */
+    
+    int i = 0;
+    for (i=0; i<scan->npoints; i++) 
+    {        
+        /* Consider only scan points representing obstacles */
+        if (scan->value[i] == OBSTACLE)
+        {
+            /* Translate and rotate scan point to robot position */
+            int x = floor(pos_x_pix + costheta * scan->x_mm[i] - sintheta * scan->y_mm[i] + 0.5);
+            int y = floor(pos_y_pix + sintheta * scan->x_mm[i] + costheta * scan->y_mm[i] + 0.5);
+         
+            /* Add point if in map bounds */
+            if (x >= 0 && x < map->size_pixels && y >= 0 && y < map->size_pixels) 
+            {
+                sum += map->pixels[y * map->size_pixels + x];
+                npoints++;
+            } 
+        }
+    } 
+
+    /* Return sum scaled by number of points, or -1 if none */
+    return npoints ? (int)(sum * 1024 / npoints) : -1;  
+}