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Optimize 'string-join'.

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* libguile/srfi-13.c (string-join): Rewrite to call 'scm_string_append'
  only once.
This commit is contained in:
Mark H Weaver 2013-04-01 03:47:29 -04:00
parent 2f13a46672
commit 786ab4258f
1 changed files with 58 additions and 65 deletions
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123
libguile/srfi-13.c
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@ -394,91 +394,84 @@ SCM_DEFINE (scm_string_join, "string-join", 1, 2, 0,
"@end table")
#define FUNC_NAME s_scm_string_join
{
#define GRAM_INFIX 0
#define GRAM_STRICT_INFIX 1
#define GRAM_SUFFIX 2
#define GRAM_PREFIX 3
SCM tmp;
SCM result;
int gram = GRAM_INFIX;
size_t del_len = 0;
long strings = scm_ilength (ls);
SCM append_list = SCM_EOL;
long list_len = scm_ilength (ls);
size_t delimiter_len = 0;
/* Validate the string list. */
if (strings < 0)
if (list_len < 0)
SCM_WRONG_TYPE_ARG (1, ls);
/* Validate the delimiter and record its length. */
if (SCM_UNBNDP (delimiter))
{
delimiter = scm_from_locale_string (" ");
del_len = 1;
delimiter_len = 1;
}
else
{
SCM_VALIDATE_STRING (2, delimiter);
del_len = scm_i_string_length (delimiter);
delimiter_len = scm_i_string_length (delimiter);
}
/* Validate the grammar symbol and remember the grammar. */
/* Validate the grammar symbol. */
if (SCM_UNBNDP (grammar))
gram = GRAM_INFIX;
else if (scm_is_eq (grammar, scm_sym_infix))
gram = GRAM_INFIX;
else if (scm_is_eq (grammar, scm_sym_strict_infix))
gram = GRAM_STRICT_INFIX;
else if (scm_is_eq (grammar, scm_sym_suffix))
gram = GRAM_SUFFIX;
else if (scm_is_eq (grammar, scm_sym_prefix))
gram = GRAM_PREFIX;
else
grammar = scm_sym_infix;
else if (!(scm_is_eq (grammar, scm_sym_infix)
|| scm_is_eq (grammar, scm_sym_strict_infix)
|| scm_is_eq (grammar, scm_sym_suffix)
|| scm_is_eq (grammar, scm_sym_prefix)))
SCM_WRONG_TYPE_ARG (3, grammar);
/* Check grammar constraints. */
if (strings == 0 && gram == GRAM_STRICT_INFIX)
SCM_MISC_ERROR ("strict-infix grammar requires non-empty list",
SCM_EOL);
result = scm_i_make_string (0, NULL, 0);
tmp = ls;
switch (gram)
if (list_len == 0)
{
case GRAM_INFIX:
case GRAM_STRICT_INFIX:
while (scm_is_pair (tmp))
{
result = scm_string_append (scm_list_2 (result, SCM_CAR (tmp)));
if (!scm_is_null (SCM_CDR (tmp)) && del_len > 0)
result = scm_string_append (scm_list_2 (result, delimiter));
tmp = SCM_CDR (tmp);
}
break;
case GRAM_SUFFIX:
while (scm_is_pair (tmp))
{
result = scm_string_append (scm_list_2 (result, SCM_CAR (tmp)));
if (del_len > 0)
result = scm_string_append (scm_list_2 (result, delimiter));
tmp = SCM_CDR (tmp);
}
break;
case GRAM_PREFIX:
while (scm_is_pair (tmp))
{
if (del_len > 0)
result = scm_string_append (scm_list_2 (result, delimiter));
result = scm_string_append (scm_list_2 (result, SCM_CAR (tmp)));
tmp = SCM_CDR (tmp);
}
break;
if (scm_is_eq (grammar, scm_sym_strict_infix))
SCM_MISC_ERROR ("strict-infix grammar requires non-empty list",
SCM_EOL);
else
/* Handle empty lists specially */
append_list = SCM_EOL;
}
else if (delimiter_len == 0)
/* Handle empty delimiters specially */
append_list = ls;
else
{
SCM *last_cdr_p = &append_list;
#define ADD_TO_APPEND_LIST(x) \
(last_cdr_p = SCM_CDRLOC (*last_cdr_p = scm_list_1 (x)))
/* Build a list of strings to pass to 'string-append'.
Here we assume that 'ls' has at least one element. */
/* If using the 'prefix' grammar, start with the delimiter. */
if (scm_is_eq (grammar, scm_sym_prefix))
ADD_TO_APPEND_LIST (delimiter);
/* Handle the first element of 'ls' specially, so that in the loop
that follows we can unconditionally insert the delimiter before
every remaining element. */
ADD_TO_APPEND_LIST (SCM_CAR (ls));
ls = SCM_CDR (ls);
/* Insert the delimiter before every remaining element. */
while (scm_is_pair (ls))
{
ADD_TO_APPEND_LIST (delimiter);
ADD_TO_APPEND_LIST (SCM_CAR (ls));
ls = SCM_CDR (ls);
}
/* If using the 'suffix' grammar, add the delimiter to the end. */
if (scm_is_eq (grammar, scm_sym_suffix))
ADD_TO_APPEND_LIST (delimiter);
#undef ADD_TO_APPEND_LIST
}
return result;
#undef GRAM_INFIX
#undef GRAM_STRICT_INFIX
#undef GRAM_SUFFIX
#undef GRAM_PREFIX
/* Construct the final result. */
return scm_string_append (append_list);
}
#undef FUNC_NAME