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Optimize empty substring case of scm_i_substring_copy

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* libguile/strings.c (scm_i_substring_copy): When asked to create an
  empty substring, use 'scm_i_make_string' to make use of its
  optimization for empty strings that reuses the global null_stringbuf.
This commit is contained in:
Mark H Weaver 2012-02-08 15:29:10 -05:00
parent d6cb0203cb
commit d5b75b6c80
1 changed files with 27 additions and 22 deletions
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49
libguile/strings.c
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@ -372,31 +372,36 @@ scm_i_substring_read_only (SCM str, size_t start, size_t end)
SCM SCM
scm_i_substring_copy (SCM str, size_t start, size_t end) scm_i_substring_copy (SCM str, size_t start, size_t end)
{ {
size_t len = end - start; if (start == end)
SCM buf, my_buf, substr; return scm_i_make_string (0, NULL, 0);
size_t str_start;
int wide = 0;
get_str_buf_start (&str, &buf, &str_start);
if (scm_i_is_narrow_string (str))
{
my_buf = make_stringbuf (len);
memcpy (STRINGBUF_CHARS (my_buf),
STRINGBUF_CHARS (buf) + str_start + start, len);
}
else else
{ {
my_buf = make_wide_stringbuf (len); size_t len = end - start;
u32_cpy ((scm_t_uint32 *) STRINGBUF_WIDE_CHARS (my_buf), SCM buf, my_buf, substr;
(scm_t_uint32 *) (STRINGBUF_WIDE_CHARS (buf) + str_start size_t str_start;
+ start), len); int wide = 0;
wide = 1; get_str_buf_start (&str, &buf, &str_start);
if (scm_i_is_narrow_string (str))
{
my_buf = make_stringbuf (len);
memcpy (STRINGBUF_CHARS (my_buf),
STRINGBUF_CHARS (buf) + str_start + start, len);
}
else
{
my_buf = make_wide_stringbuf (len);
u32_cpy ((scm_t_uint32 *) STRINGBUF_WIDE_CHARS (my_buf),
(scm_t_uint32 *) (STRINGBUF_WIDE_CHARS (buf) + str_start
+ start), len);
wide = 1;
}
scm_remember_upto_here_1 (buf);
substr = scm_double_cell (STRING_TAG, SCM_UNPACK (my_buf),
(scm_t_bits) 0, (scm_t_bits) len);
if (wide)
scm_i_try_narrow_string (substr);
return substr;
} }
scm_remember_upto_here_1 (buf);
substr = scm_double_cell (STRING_TAG, SCM_UNPACK (my_buf),
(scm_t_bits) 0, (scm_t_bits) len);
if (wide)
scm_i_try_narrow_string (substr);
return substr;
} }
SCM SCM