Enable --version-sort on systems without strverscmp()

The --version-sort option requires strverscmp(), but this is a glibc
extension that does not exist on OpenBSD and other systems. To enable
--version-sort on those systems, provide an internal implementation of
strverscmp(). The implementation is from the musl C library and is
MIT-licensed.

The build process remains the same: the verscmp flag should be set to 1
only if strverscmp() is available in libc. If verscmp is 0, then the
internal implementation is used.

9 files changed, 67 insertions, 19 deletions

diff --git a/README.md b/README.md
index 2289b6b..2cedc53 100644
--- a/README.md
+++ b/README.md
@@ -91,7 +91,7 @@ indicates that the corresponding feature is enabled by default.
 | help | 0 | include help text (refers to the manpage otherwise) |
 | inotify | 0 | enable inotify, needed for `--auto-reload` |
 | stat64 | 0 | Support CIFS shares from 64bit hosts on 32bit machines |
-| verscmp | 1 | Support naturing sorting (`--version-sort`). Requires a GNU-compatible libc exposing `strverscmp` |
+| verscmp | 1 | Whether your libc provides `strvercmp()`. If set to 0, feh will use an internal implementation. |
 | xinerama | 1 | Support Xinerama/XRandR multiscreen setups |
 
 For example, `make xinerama=0 debug=1` will disable Xinerama support and
diff --git a/config.mk b/config.mk
index 0a8c0e4..5dfd7d3 100644
--- a/config.mk
+++ b/config.mk
@@ -64,10 +64,7 @@ ifeq (${stat64},1)
 endif
 
 ifeq (${verscmp},1)
-	CFLAGS += -DHAVE_VERSCMP
-	MAN_VERSCMP = available
-else
-	MAN_VERSCMP = not available
+	CFLAGS += -DHAVE_STRVERSCMP
 endif
 
 ifeq (${xinerama},1)
diff --git a/man/Makefile b/man/Makefile
index acf8629..3be07e3 100644
--- a/man/Makefile
+++ b/man/Makefile
@@ -13,7 +13,6 @@ all: ${TARGETS}
 	-e 's/\$$MAN_DEBUG\$$/${MAN_DEBUG}/' \
 	-e 's/\$$MAN_EXIF\$$/${MAN_EXIF}/' \
 	-e 's/\$$MAN_INOTIFY\$$/${MAN_INOTIFY}/' \
-	-e 's/\$$MAN_VERSCMP\$$/${MAN_VERSCMP}/' \
 	-e 's/\$$MAN_XINERAMA\$$/${MAN_XINERAMA}/' \
 	< ${@:.1=.pre} > $@
 
diff --git a/man/feh.pre b/man/feh.pre
index c6dae5f..a27f042 100644
--- a/man/feh.pre
+++ b/man/feh.pre
@@ -32,9 +32,6 @@ Compile-time switches in this build:
 remote file support: libcurl $MAN_CURL$
 .
 .It
-natural sorting option $MAN_VERSCMP$
-.
-.It
 Xinerama multi-monitor support $MAN_XINERAMA$
 .
 .It
@@ -887,7 +884,6 @@ output version information and exit.
 .
 .It Cm --version-sort
 .
-.Pq optional feature, $MAN_VERSCMP$ in this build
 When combined with
 .Cm --sort name , --sort filename ,
 or
diff --git a/src/Makefile b/src/Makefile
index ac4d2fe..10e33eb 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -34,6 +34,10 @@ ifeq (${exif},1)
 		exif_nikon.c
 endif
 
+ifneq (${verscmp},1)
+	TARGETS += strverscmp.c
+endif
+
 OBJECTS = ${TARGETS:.c=.o}
 
 I_SRCS = ${shell echo *.raw}
diff --git a/src/feh.h b/src/feh.h
index a76d66f..e735871 100644
--- a/src/feh.h
+++ b/src/feh.h
@@ -31,7 +31,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  * strverscmp(3) is a GNU extension. In most supporting C libraries it
  * requires _GNU_SOURCE to be defined.
  */
-#ifdef HAVE_VERSCMP
+#ifdef HAVE_STRVERSCMP
 #define _GNU_SOURCE
 #endif
 
@@ -182,6 +182,9 @@ gib_list *feh_list_jump(gib_list * root, gib_list * l, int direction, int num);
 #ifdef HAVE_INOTIFY
 void feh_event_handle_inotify(void);
 #endif
+#ifndef HAVE_STRVERSCMP
+int strverscmp(const char *l0, const char *r0);
+#endif
 
 /* Imlib stuff */
 extern Display *disp;
diff --git a/src/filelist.c b/src/filelist.c
index 4939d4d..361ac19 100644
--- a/src/filelist.c
+++ b/src/filelist.c
@@ -402,7 +402,6 @@ void feh_file_dirname(char *dst, feh_file * f, int maxlen)
 	dst[n] = '\0';
 }
 
-#ifdef HAVE_VERSCMP
 static inline int strcmp_or_strverscmp(const char *s1, const char *s2)
 {
 	if (!opt.version_sort)
@@ -410,9 +409,6 @@ static inline int strcmp_or_strverscmp(const char *s1, const char *s2)
 	else
 		return(strverscmp(s1, s2));
 }
-#else
-#define strcmp_or_strverscmp strcmp
-#endif
 
 int feh_cmp_filename(void *file1, void *file2)
 {
diff --git a/src/options.c b/src/options.c
index 2cd7a9e..a92b1ff 100644
--- a/src/options.c
+++ b/src/options.c
@@ -943,10 +943,6 @@ static void show_version(void)
 		"stat64 "
 #endif
 
-#ifdef HAVE_VERSCMP
-		"verscmp "
-#endif
-
 #ifdef HAVE_LIBXINERAMA
 		"xinerama "
 #endif
diff --git a/src/strverscmp.c b/src/strverscmp.c
new file mode 100644
index 0000000..92cd877
--- /dev/null
+++ b/src/strverscmp.c
@@ -0,0 +1,57 @@
+/*
+ * Copyright © 2005-2020 Rich Felker, et al.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#define _GNU_SOURCE
+#include <ctype.h>
+#include <string.h>
+
+int strverscmp(const char *l0, const char *r0)
+{
+	const unsigned char *l = (const void *)l0;
+	const unsigned char *r = (const void *)r0;
+	size_t i, dp, j;
+	int z = 1;
+
+	/* Find maximal matching prefix and track its maximal digit
+	 * suffix and whether those digits are all zeros. */
+	for (dp=i=0; l[i]==r[i]; i++) {
+		int c = l[i];
+		if (!c) return 0;
+		if (!isdigit(c)) dp=i+1, z=1;
+		else if (c!='0') z=0;
+	}
+
+	if (l[dp]!='0' && r[dp]!='0') {
+		/* If we're not looking at a digit sequence that began
+		 * with a zero, longest digit string is greater. */
+		for (j=i; isdigit(l[j]); j++)
+			if (!isdigit(r[j])) return 1;
+		if (isdigit(r[j])) return -1;
+	} else if (z && dp<i && (isdigit(l[i]) || isdigit(r[i]))) {
+		/* Otherwise, if common prefix of digit sequence is
+		 * all zeros, digits order less than non-digits. */
+		return (unsigned char)(l[i]-'0') - (unsigned char)(r[i]-'0');
+	}
+
+	return l[i] - r[i];
+}