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diff --git a/potrace/progress.h b/potrace/progress.h
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+/* Copyright (C) 2001-2007 Peter Selinger.
+ *  This file is part of Potrace. It is free software and it is covered
+ *  by the GNU General Public License. See the file COPYING for details. */
+
+/* operations on potrace_progress_t objects, which are defined in
+ *  potracelib.h. Note: the code attempts to minimize runtime overhead
+ *  when no progress monitoring was requested. It also tries to
+ *  minimize excessive progress calculations beneath the "epsilon"
+ *  threshold. */
+
+#ifndef PROGRESS_H
+#define PROGRESS_H
+
+/* structure to hold progress bar callback data */
+struct progress_s
+{
+    void   (* callback)( double progress, void* privdata ); /* callback fn */
+    void*  data;                                            /* callback function's private data */
+    double min, max;                                        /* desired range of progress, e.g. 0.0 to 1.0 */
+    double epsilon;                                         /* granularity: can skip smaller increments */
+    double b;                                               /* upper limit of subrange in superrange units */
+    double d_prev;                                          /* previous value of d */
+};
+typedef struct progress_s progress_t;
+
+/* notify given progress object of current progress. Note that d is
+ *  given in the 0.0-1.0 range, which will be scaled and translated to
+ *  the progress object's range. */
+static inline void progress_update( double d, progress_t* prog )
+{
+    double d_scaled;
+
+    if( prog->callback != NULL )
+    {
+        d_scaled = prog->min * (1 - d) + prog->max * d;
+        if( d == 1.0 || d_scaled >= prog->d_prev + prog->epsilon )
+        {
+            prog->callback( prog->min * (1 - d) + prog->max * d, prog->data );
+            prog->d_prev = d_scaled;
+        }
+    }
+}
+
+
+/* start a subrange of the given progress object. The range is
+ *  narrowed to [a..b], relative to 0.0-1.0 coordinates. If new range
+ *  is below granularity threshold, disable further subdivisions. */
+static inline void progress_subrange_start( double            a,
+                                            double            b,
+                                            const progress_t* prog,
+                                            progress_t*       sub )
+{
+    double min, max;
+
+    if( prog->callback == NULL )
+    {
+        sub->callback = NULL;
+        return;
+    }
+
+    min = prog->min * (1 - a) + prog->max * a;
+    max = prog->min * (1 - b) + prog->max * b;
+
+    if( max - min < prog->epsilon )
+    {
+        sub->callback = NULL; /* no further progress info in subrange */
+        sub->b = b;
+        return;
+    }
+    sub->callback = prog->callback;
+    sub->data     = prog->data;
+    sub->epsilon  = prog->epsilon;
+    sub->min    = min;
+    sub->max    = max;
+    sub->d_prev = prog->d_prev;
+    return;
+}
+
+
+static inline void progress_subrange_end( progress_t* prog, progress_t* sub )
+{
+    if( prog->callback != NULL )
+    {
+        if( sub->callback == NULL )
+        {
+            progress_update( sub->b, prog );
+        }
+        else
+        {
+            prog->d_prev = sub->d_prev;
+        }
+    }
+}
+
+
+#endif /* PROGRESS_H */