[Guile-commits] 01/02: 'string->symbol' avoids copying the underlying string.

[Ludovic Courtès]

civodul pushed a commit to branch main
in repository guile.

commit 032acdeac9dfe6b407a1fcbd9f00c3e1a0dd27aa
Author: Ludovic Courtès <ludo@gnu.org>
AuthorDate: Sat Feb 5 23:27:48 2022 +0100

    'string->symbol' avoids copying the underlying string.
    
    * libguile/strings.c (scm_i_make_symbol): Reuse NAME's stringbuf unless
    it's mutable or NAME starts at a non-zero offset or has a different
    length.
---
 libguile/strings.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/libguile/strings.c b/libguile/strings.c
index a5b4b0386..5eebb3300 100644
--- a/libguile/strings.c
+++ b/libguile/strings.c
@@ -763,10 +763,16 @@ SCM
 scm_i_make_symbol (SCM name, scm_t_bits flags, unsigned long hash)
 {
   SCM buf, symbol;
-  size_t length = STRING_LENGTH (name);
+  size_t start, length = STRING_LENGTH (name);
 
-  name = scm_i_substring_copy (name, 0, length);
-  buf = STRING_STRINGBUF (name);
+  get_str_buf_start (&name, &buf, &start);
+  if (SCM_UNLIKELY (STRINGBUF_MUTABLE (buf)
+                    || start != 0
+                    || STRINGBUF_LENGTH (buf) != length))
+    {
+      name = scm_i_substring_copy (name, 0, length);
+      buf = STRING_STRINGBUF (name);
+    }
 
   symbol = scm_words (scm_tc7_symbol | flags, 3);
   SCM_SET_CELL_WORD_1 (symbol, SCM_UNPACK (buf));