Gambit prelude addition for bv2string

[gambiteer]

firefly:~/programs/r7rs-benchmarks> git diff src/GambitC-prelude.scm
diff --git a/src/GambitC-prelude.scm b/src/GambitC-prelude.scm
index 51ffde0..73f9cdd 100644
--- a/src/GambitC-prelude.scm
+++ b/src/GambitC-prelude.scm
@@ -35,6 +35,23 @@
 (define write-string write)

 (define (this-scheme-implementation-name) (string-append "gambitc-" (system-version-string)))
+
+(define (string->utf8 s)
+  (with-output-to-u8vector
+   '()
+   (lambda ()
+     (display s))))
+
+(define (utf8->string v)
+  (call-with-input-u8vector
+   v
+   (lambda (p)
+     (list->string (read-all p read-char)))))
+
+(define make-bytevector make-u8vector)
+
+(define bytevector-u8-set! u8vector-set!)
+
 ;; TODO: load syntax-case here, to get syntax-rules.
 ;; google says (load "~~/syntax-case"), but that doesn't work on my machine :-/

I'm not sure that these lines in the femtolisp prelude:

+(define utf8->string identity)
+(define string->utf8 identity) 

are really true---are utf8-encoded strings really just byte-vectors in femtolisp? It does make the benchmark to faster, though!

[gambiteer]

Here is an improved patch (doesn't depend on default setting of built gambit):

firefly:~/programs/r7rs-benchmarks> git diff src/GambitC-prelude.scm 
diff --git a/src/GambitC-prelude.scm b/src/GambitC-prelude.scm
index 51ffde0..09e7e64 100644
--- a/src/GambitC-prelude.scm
+++ b/src/GambitC-prelude.scm
@@ -35,6 +35,21 @@
 (define write-string write)

 (define (this-scheme-implementation-name) (string-append "gambitc-" (system-version-string)))
+
+(define (string->utf8 s)
+  (with-output-to-u8vector
+   (list char-encoding: 'UTF-8)
+   (lambda ()
+     (display s))))
+
+(define (utf8->string v)
+  (let ((p (open-input-u8vector (list char-encoding: 'UTF-8 init: v))))
+    (list->string (read-all p read-char))))
+
+(define make-bytevector make-u8vector)
+
+(define bytevector-u8-set! u8vector-set!)
+
 ;; TODO: load syntax-case here, to get syntax-rules.
 ;; google says (load "~~/syntax-case"), but that doesn't work on my machine :-/

[gambiteer]

This one uses Gambit's builtin functions better:

firefly:~/programs/r7rs-benchmarks> git diff src/GambitC-prelude.scm 
diff --git a/src/GambitC-prelude.scm b/src/GambitC-prelude.scm
index 51ffde0..af07f2a 100644
--- a/src/GambitC-prelude.scm
+++ b/src/GambitC-prelude.scm
@@ -35,6 +35,25 @@
 (define write-string write)

 (define (this-scheme-implementation-name) (string-append "gambitc-" (system-version-string)))
+
+(define (string->utf8 s)
+  (with-output-to-u8vector
+   (list char-encoding: 'UTF-8)
+   (lambda ()
+     (display s))))
+
+(define (utf8->string bstr #!optional (enc 'UTF-8))
+  (let* ((in (open-input-u8vector `(char-encoding: ,enc init: ,bstr)))
+         (len (u8vector-length bstr))
+         (out (make-string len))
+         (n (read-substring out 0 len in)))
+    (string-shrink! out n)
+    out))
+
+(define make-bytevector make-u8vector)
+
+(define bytevector-u8-set! u8vector-set!)
+
 ;; TODO: load syntax-case here, to get syntax-rules.
 ;; google says (load "~~/syntax-case"), but that doesn't work on my machine :-/