[Guile-commits] 05/07: Move scm_c_shrink_bytevector off realloc

[Andy Wingo]

wingo pushed a commit to branch wip-whippet
in repository guile.

commit f3649d7d1bf28790c882785dd2b3c2f5935c8d7a
Author: Andy Wingo <wi...@pobox.com>
AuthorDate: Wed Apr 30 11:01:14 2025 +0200

    Move scm_c_shrink_bytevector off realloc
    
    * libguile/bytevectors.c (scm_c_shrink_bytevector): Return buf as is if
    length is more than half of previous.  Otherwise make a fresh buffer and
    copy.
---
 libguile/bytevectors.c | 33 +++++++++------------------------
 1 file changed, 9 insertions(+), 24 deletions(-)

diff --git a/libguile/bytevectors.c b/libguile/bytevectors.c
index 6b14c7246..2ec26730b 100644
--- a/libguile/bytevectors.c
+++ b/libguile/bytevectors.c
@@ -1,4 +1,4 @@
-/* Copyright 2009-2015,2018-2019,2023
+/* Copyright 2009-2015,2018-2019,2023,2025
      Free Software Foundation, Inc.
 
    This file is part of Guile.
@@ -394,40 +394,25 @@ SCM_DEFINE (scm_bytevector_slice, "bytevector-slice", 2, 
1, 0,
 SCM
 scm_c_shrink_bytevector (SCM bv, size_t c_new_len)
 {
-  SCM new_bv;
-  size_t c_len;
-
   if (SCM_UNLIKELY (c_new_len % SCM_BYTEVECTOR_TYPE_SIZE (bv)))
     /* This would be an internal Guile programming error */
     abort ();
 
-  c_len = SCM_BYTEVECTOR_LENGTH (bv);
+  size_t c_len = SCM_BYTEVECTOR_LENGTH (bv);
   if (SCM_UNLIKELY (c_new_len > c_len))
     abort ();
 
-  SCM_BYTEVECTOR_SET_LENGTH (bv, c_new_len);
-
-  if (SCM_BYTEVECTOR_CONTIGUOUS_P (bv))
+  if (SCM_BYTEVECTOR_CONTIGUOUS_P (bv) && c_new_len > c_len / 2) 
     {
-      signed char *c_bv;
-
-      c_bv = scm_gc_realloc (SCM2PTR (bv),
-                            c_len + SCM_BYTEVECTOR_HEADER_BYTES,
-                            c_new_len + SCM_BYTEVECTOR_HEADER_BYTES,
-                            SCM_GC_BYTEVECTOR);
-      new_bv = PTR2SCM (c_bv);
-      SCM_BYTEVECTOR_SET_CONTENTS (new_bv, c_bv + SCM_BYTEVECTOR_HEADER_BYTES);
+      SCM_BYTEVECTOR_SET_LENGTH (bv, c_new_len);
+      return bv;
     }
-  else
-    {
-      signed char *c_bv;
 
-      c_bv = scm_gc_realloc (SCM_BYTEVECTOR_CONTENTS (bv),
-                            c_len, c_new_len, SCM_GC_BYTEVECTOR);
-      SCM_BYTEVECTOR_SET_CONTENTS (bv, c_bv);
+  SCM new_bv =
+    scm_i_make_typed_bytevector (c_new_len, SCM_BYTEVECTOR_ELEMENT_TYPE (bv));
 
-      new_bv = bv;
-    }
+  memcpy (SCM_BYTEVECTOR_CONTENTS (new_bv), SCM_BYTEVECTOR_CONTENTS (bv),
+          c_new_len);
 
   return new_bv;
 }