tag: support --sort=<spec>

--sort=version:refname (or --sort=v:refname for short) sorts tags as
if they are versions. --sort=-refname reverses the order (with or
without ":version").

versioncmp() is copied from string/strverscmp.c in glibc commit
ee9247c38a8def24a59eb5cfb7196a98bef8cfdc, reformatted to Git coding
style. The implementation is under LGPL-2.1 and according to [1] I can
relicense it to GPLv2.

[1] http://www.gnu.org/licenses/gpl-faq.html#AllCompatibility

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 93 insertions, 0 deletions

diff --git a/versioncmp.c b/versioncmp.c
new file mode 100644
index 0000000..7511e08
--- /dev/null
+++ b/versioncmp.c
@@ -0,0 +1,93 @@
+#include "cache.h"
+
+/*
+ * versioncmp(): copied from string/strverscmp.c in glibc commit
+ * ee9247c38a8def24a59eb5cfb7196a98bef8cfdc, reformatted to Git coding
+ * style. The implementation is under LGPL-2.1 and Git relicenses it
+ * to GPLv2.
+ */
+
+/*
+ * states: S_N: normal, S_I: comparing integral part, S_F: comparing
+ * fractionnal parts, S_Z: idem but with leading Zeroes only
+ */
+#define  S_N    0x0
+#define  S_I    0x3
+#define  S_F    0x6
+#define  S_Z    0x9
+
+/* result_type: CMP: return diff; LEN: compare using len_diff/diff */
+#define  CMP    2
+#define  LEN    3
+
+
+/*
+ * Compare S1 and S2 as strings holding indices/version numbers,
+ * returning less than, equal to or greater than zero if S1 is less
+ * than, equal to or greater than S2 (for more info, see the texinfo
+ * doc).
+ */
+
+int versioncmp(const char *s1, const char *s2)
+{
+	const unsigned char *p1 = (const unsigned char *) s1;
+	const unsigned char *p2 = (const unsigned char *) s2;
+	unsigned char c1, c2;
+	int state, diff;
+
+	/*
+	 * Symbol(s)    0       [1-9]   others
+	 * Transition   (10) 0  (01) d  (00) x
+	 */
+	static const uint8_t next_state[] = {
+		/* state    x    d    0  */
+		/* S_N */  S_N, S_I, S_Z,
+		/* S_I */  S_N, S_I, S_I,
+		/* S_F */  S_N, S_F, S_F,
+		/* S_Z */  S_N, S_F, S_Z
+	};
+
+	static const int8_t result_type[] = {
+		/* state   x/x  x/d  x/0  d/x  d/d  d/0  0/x  0/d  0/0  */
+
+		/* S_N */  CMP, CMP, CMP, CMP, LEN, CMP, CMP, CMP, CMP,
+		/* S_I */  CMP, -1,  -1,  +1,  LEN, LEN, +1,  LEN, LEN,
+		/* S_F */  CMP, CMP, CMP, CMP, CMP, CMP, CMP, CMP, CMP,
+		/* S_Z */  CMP, +1,  +1,  -1,  CMP, CMP, -1,  CMP, CMP
+	};
+
+	if (p1 == p2)
+		return 0;
+
+	c1 = *p1++;
+	c2 = *p2++;
+	/* Hint: '0' is a digit too.  */
+	state = S_N + ((c1 == '0') + (isdigit (c1) != 0));
+
+	while ((diff = c1 - c2) == 0) {
+		if (c1 == '\0')
+			return diff;
+
+		state = next_state[state];
+		c1 = *p1++;
+		c2 = *p2++;
+		state += (c1 == '0') + (isdigit (c1) != 0);
+	}
+
+	state = result_type[state * 3 + (((c2 == '0') + (isdigit (c2) != 0)))];
+
+	switch (state) {
+	case CMP:
+		return diff;
+
+	case LEN:
+		while (isdigit (*p1++))
+			if (!isdigit (*p2++))
+				return 1;
+
+		return isdigit (*p2) ? -1 : diff;
+
+	default:
+		return state;
+	}
+}