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Optimize scm_ilength and 'length+'.

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* libguile/list.c (scm_ilength): Test for SCM_NULL_OR_NIL_P only after
  testing scm_is_pair.  Conform to GNU coding standards.

* libguile/srfi-1.c (scm_srfi1_length_plus): Ditto.
This commit is contained in:
Mark H Weaver 2014-06-04 20:42:21 -04:00
parent 4afca1a066
commit fc8a90043b
2 changed files with 31 additions and 22 deletions
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31
libguile/list.c
View file

@ -1,5 +1,5 @@
/* Copyright (C) 1995,1996,1997,2000,2001,2003,2004,2008,2009,2010,2011 /* Copyright (C) 1995-1997, 2000, 2001, 2003, 2004, 2008-2011,
* Free Software Foundation, Inc. * 2014 Free Software Foundation, Inc.
* *
* This library is free software; you can redistribute it and/or * This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License * modify it under the terms of the GNU Lesser General Public License
@ -179,24 +179,25 @@ SCM_DEFINE (scm_list_p, "list?", 1, 0, 0,
long" lists (i.e. lists with cycles in their cdrs), and returns -1 long" lists (i.e. lists with cycles in their cdrs), and returns -1
if it does find one. */ if it does find one. */
long long
scm_ilength(SCM sx) scm_ilength (SCM sx)
{ {
long i = 0; long i = 0;
SCM tortoise = sx; SCM tortoise = sx;
SCM hare = sx; SCM hare = sx;
do { do
if (SCM_NULL_OR_NIL_P(hare)) return i; {
if (!scm_is_pair (hare)) return -1; if (!scm_is_pair (hare))
hare = SCM_CDR(hare); return SCM_NULL_OR_NIL_P (hare) ? i : -1;
i++; hare = SCM_CDR (hare);
if (SCM_NULL_OR_NIL_P(hare)) return i; i++;
if (!scm_is_pair (hare)) return -1; if (!scm_is_pair (hare))
hare = SCM_CDR(hare); return SCM_NULL_OR_NIL_P (hare) ? i : -1;
i++; hare = SCM_CDR (hare);
/* For every two steps the hare takes, the tortoise takes one. */ i++;
tortoise = SCM_CDR(tortoise); /* For every two steps the hare takes, the tortoise takes one. */
} tortoise = SCM_CDR (tortoise);
}
while (!scm_is_eq (hare, tortoise)); while (!scm_is_eq (hare, tortoise));
/* If the tortoise ever catches the hare, then the list must contain /* If the tortoise ever catches the hare, then the list must contain

22
libguile/srfi-1.c
View file

@ -620,20 +620,28 @@ SCM_DEFINE (scm_srfi1_length_plus, "length+", 1, 0, 0,
do do
{ {
if (SCM_NULL_OR_NIL_P (hare))
return scm_from_size_t (i);
if (!scm_is_pair (hare)) if (!scm_is_pair (hare))
scm_wrong_type_arg_msg (FUNC_NAME, 1, lst, "proper or circular list"); {
if (SCM_NULL_OR_NIL_P (hare))
return scm_from_size_t (i);
else
scm_wrong_type_arg_msg (FUNC_NAME, 1, lst,
"proper or circular list");
}
hare = SCM_CDR (hare); hare = SCM_CDR (hare);
i++; i++;
if (SCM_NULL_OR_NIL_P (hare))
return scm_from_size_t (i);
if (!scm_is_pair (hare)) if (!scm_is_pair (hare))
scm_wrong_type_arg_msg (FUNC_NAME, 1, lst, "proper or circular list"); {
if (SCM_NULL_OR_NIL_P (hare))
return scm_from_size_t (i);
else
scm_wrong_type_arg_msg (FUNC_NAME, 1, lst,
"proper or circular list");
}
hare = SCM_CDR (hare); hare = SCM_CDR (hare);
i++; i++;
/* For every two steps the hare takes, the tortoise takes one. */ /* For every two steps the hare takes, the tortoise takes one. */
tortoise = SCM_CDR(tortoise); tortoise = SCM_CDR (tortoise);
} }
while (!scm_is_eq (hare, tortoise)); while (!scm_is_eq (hare, tortoise));