config/git: import suckless sbase

i currently use the output of sha512sum in several
places of xbmk, which is a bit unreliable in case
output changes.

other cases where i use util outputs in variables
are probably reliable, because i'm using mostly
posix utilities in those.

to mitigate this, i now import suckless sbase, which
has a reasonable sha512sum implementation.

*every* binary it builds is being placed in build.list,
because i'll probably start using more of them.

for example, i may start modifying the "date"
implementation, adding the GNU-specific options that
i need as mentioned on init.sh

i'm importing it in util/ because the sha512sum
util is needed for verifying project sources, so
if sbase itself is a "project source", that means
we can into a chicken and egg bootstrapping problem.

this is sbase at revision:
055cc1ae1b3a13c3d8f25af0a4a3316590efcd48

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/sbase/libutil/unescape.c

@@ -0,0 +1,58 @@
+/* See LICENSE file for copyright and license details. */
+#include <ctype.h>
+#include <string.h>
+
+#include "../util.h"
+
+#define is_odigit(c)  ('0' <= c && c <= '7')
+
+size_t
+unescape(char *s)
+{
+	static const char escapes[256] = {
+		['"'] = '"',
+		['\''] = '\'',
+		['\\'] = '\\',
+		['a'] = '\a',
+		['b'] = '\b',
+		['E'] = 033,
+		['e'] = 033,
+		['f'] = '\f',
+		['n'] = '\n',
+		['r'] = '\r',
+		['t'] = '\t',
+		['v'] = '\v'
+	};
+	size_t m, q;
+	char *r, *w;
+
+	for (r = w = s; *r;) {
+		if (*r != '\\') {
+			*w++ = *r++;
+			continue;
+		}
+		r++;
+		if (!*r) {
+			eprintf("null escape sequence\n");
+		} else if (escapes[(unsigned char)*r]) {
+			*w++ = escapes[(unsigned char)*r++];
+		} else if (is_odigit(*r)) {
+			for (q = 0, m = 3; m && is_odigit(*r); m--, r++)
+				q = q * 8 + (*r - '0');
+			*w++ = MIN(q, 255);
+		} else if (*r == 'x' && isxdigit(r[1])) {
+			r++;
+			for (q = 0, m = 2; m && isxdigit(*r); m--, r++)
+				if (isdigit(*r))
+					q = q * 16 + (*r - '0');
+				else
+					q = q * 16 + (tolower(*r) - 'a' + 10);
+			*w++ = q;
+		} else {
+			eprintf("invalid escape sequence '\\%c'\n", *r);
+		}
+	}
+	*w = '\0';
+
+	return w - s;
+}