Index: libucdf/tester.c
===================================================================
--- libucdf/tester.c	(revision 35429)
+++ libucdf/tester.c	(revision 35430)
@@ -43,6 +43,21 @@
 	return 0;
 }
 
+static int print_file_at(ucdf_ctx_t *ctx, ucdf_direntry_t *de, long offs, long len)
+{
+	ucdf_file_t fp;
+	char tmp[1024];
+
+	if (ucdf_fopen(ctx, &fp, de) != 0)
+		return -1;
+
+	printf(" seek to %ld: %d\n", offs, ucdf_fseek(&fp, offs));
+	printf(" read %ld: %ld\n", len, ucdf_fread(&fp, tmp, len));
+	fwrite(tmp, len, 1, stdout);
+	printf("\n");
+	return 0;
+}
+
 int main(int argc, char *argv[])
 {
 	char *fn = "A.PcbDoc";
@@ -68,6 +83,11 @@
 		print_dir(&ctx, de, 0);
 		printf("==\n");
 		dump_file(&ctx, de);
+		printf("==\n");
+		print_file_at(&ctx, de, 39384, 10);
+		print_file_at(&ctx, de, 39385, 10);
+		print_file_at(&ctx, de, 39386, 10);
+		print_file_at(&ctx, de, 39387, 10);
 	}
 
 	ucdf_close(&ctx);
Index: libucdf/ucdf.c
===================================================================
--- libucdf/ucdf.c	(revision 35429)
+++ libucdf/ucdf.c	(revision 35430)
@@ -480,3 +480,50 @@
 	return ucdf_fread_long(fp, dst, len);
 }
 
+
+int ucdf_fseek(ucdf_file_t *fp, long offs)
+{
+	ucdf_ctx_t *ctx = fp->ctx;
+	long sect_min, sect_max;
+	long sect_idx, sect_offs, sect_id, n;
+
+	if (fp->de->is_short)
+		return -1;
+
+	if (offs == fp->stream_offs)
+		return 0; /* no need to move */
+
+	if ((offs < 0) || (offs >= fp->de->size))
+		return -1; /* do not seek out of the file */
+
+	/* fast lane: check if seek is within the current sector */
+	sect_min = fp->stream_offs - fp->sect_offs;
+	sect_max = sect_min + ctx->sect_size;
+	if ((offs >= sect_min) && (offs < sect_max)) {
+		long delta = offs - fp->stream_offs;
+		fp->stream_offs += delta;
+		fp->sect_offs += delta;
+		return 0;
+	}
+
+	/* seeking to another sector; since SAT is a singly linked list, we need
+	   to recalculate this sector by sector */
+	sect_idx = offs / ctx->sect_size;
+	sect_offs = offs % ctx->sect_size;
+
+	sect_id = fp->de->first;
+	for(n = 0; n < sect_idx; n++) {
+		if (sect_id < 0)
+			return -1;
+		sect_id = ctx->sat[sect_id];
+	}
+
+	if (sect_id < 0)
+		return -1;
+
+	fp->stream_offs += offs;
+	fp->sect_offs += sect_offs;
+	fp->sect_id = sect_id;
+	return 0;
+}
+
Index: libucdf/ucdf.h
===================================================================
--- libucdf/ucdf.h	(revision 35429)
+++ libucdf/ucdf.h	(revision 35430)
@@ -88,4 +88,9 @@
    ends short, returns less than len. If stream is already at EOF, returns 0 */
 long ucdf_fread(ucdf_file_t *fp, char *dst, long len);
 
+/* Seek to a given byte offset from the beginning of the stream. Returns 0
+   on success or -1 on error (in which case no seek is done). At the moment
+   only long files are supported. */
+int ucdf_fseek(ucdf_file_t *fp, long offs);
 
+