utf8: Errors in xstring-copy! and utf8-case-map

[sjamaan]

utf8-srfi-13 has a problem where it's missing a set of parentheses; it's passing the procedure - as one of the arguments to +, causing an infinite loop in string-xcopy!:

#;1> (use utf8-srfi-13)
#;2> (define s1 "foo")
#;3> (define s2 (make-string 3))
#;4> (string-xcopy! s2 0 s1 1)
;; never stops, should put "oof" in s2

This is simple to fix:

Index: utf8-srfi-13.scm
===================================================================
--- utf8-srfi-13.scm	(revision 26685)
+++ utf8-srfi-13.scm	(working copy)
@@ -570,7 +570,7 @@
 
 (define (string-xcopy target tstart s from . opt)
   (let-optionals* opt ((to1 #f) (start 0) (end (utf8-string-length s)))
-    (let ((to (or to1 (+ from - end start))))
+    (let ((to (or to1 (+ from (- end start)))))
       (string-append (utf8-substring target 0 tstart)
                      (xsubstring s from to start end)
                      (utf8-substring target

There's another bug in utf8-case-map, which I don't know how to trigger (might be worthwhile trying to figure that out to add it as a regression test). There's two places where u32vector-ref is called with only one argument. This is also simple to fix, but as I wasn't able to trigger the bug I'm not sure this is correct:

Index: utf8-case-map.scm
===================================================================
--- utf8-case-map.scm	(revision 26685)
+++ utf8-case-map.scm	(working copy)
@@ -122,9 +122,9 @@
      (>= hi lo)
      (cond
        ((= i (u32vector-ref tab (* lo 4)))
-        (u32vector-ref (+ (* lo 4) off)))
+        (u32vector-ref tab (+ (* lo 4) off)))
        ((= i (u32vector-ref tab (* hi 4)))
-        (u32vector-ref (+ (* hi 4) off)))
+        (u32vector-ref tab (+ (* hi 4) off)))
        (else
         (let loop ((a lo) (b hi))
           (if (= a b)

These bugs were found by the scrutinizer, see ​http://parenteses.org/mario/misc/specialize-report/install/utf8.html