1 files changed, 140 insertions, 0 deletions
diff --git a/base85.c b/base85.c
new file mode 100644
index 0000000..b88270f
--- /dev/null
+++ b/base85.c
@@ -0,0 +1,140 @@
+#include "cache.h"
+
+#undef DEBUG_85
+
+#ifdef DEBUG_85
+#define say(a) fprintf(stderr, a)
+#define say1(a,b) fprintf(stderr, a, b)
+#define say2(a,b,c) fprintf(stderr, a, b, c)
+#else
+#define say(a) do {} while(0)
+#define say1(a,b) do {} while(0)
+#define say2(a,b,c) do {} while(0)
+#endif
+
+static const char en85[] = {
+	'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
+	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
+	'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
+	'U', 'V', 'W', 'X', 'Y', 'Z',
+	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
+	'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
+	'u', 'v', 'w', 'x', 'y', 'z',
+	'!', '#', '$', '%', '&', '(', ')', '*', '+', '-',
+	';', '<', '=', '>', '?', '@', '^', '_',	'`', '{',
+	'|', '}', '~'
+};
+
+static char de85[256];
+static void prep_base85(void)
+{
+	int i;
+	if (de85['Z'])
+		return;
+	for (i = 0; i < ARRAY_SIZE(en85); i++) {
+		int ch = en85[i];
+		de85[ch] = i + 1;
+	}
+}
+
+int decode_85(char *dst, const char *buffer, int len)
+{
+	prep_base85();
+
+	say2("decode 85 <%.*s>", len/4*5, buffer);
+	while (len) {
+		unsigned acc = 0;
+		int de, cnt = 4;
+		unsigned char ch;
+		do {
+			ch = *buffer++;
+			de = de85[ch];
+			if (--de < 0)
+				return error("invalid base85 alphabet %c", ch);
+			acc = acc * 85 + de;
+		} while (--cnt);
+		ch = *buffer++;
+		de = de85[ch];
+		if (--de < 0)
+			return error("invalid base85 alphabet %c", ch);
+		/*
+		 * Detect overflow.  The largest
+		 * 5-letter possible is "|NsC0" to
+		 * encode 0xffffffff, and "|NsC" gives
+		 * 0x03030303 at this point (i.e.
+		 * 0xffffffff = 0x03030303 * 85).
+		 */
+		if (0x03030303 < acc ||
+		    0xffffffff - de < (acc *= 85))
+			return error("invalid base85 sequence %.5s", buffer-5);
+		acc += de;
+		say1(" %08x", acc);
+
+		cnt = (len < 4) ? len : 4;
+		len -= cnt;
+		do {
+			acc = (acc << 8) | (acc >> 24);
+			*dst++ = acc;
+		} while (--cnt);
+	}
+	say("\n");
+
+	return 0;
+}
+
+void encode_85(char *buf, const unsigned char *data, int bytes)
+{
+	prep_base85();
+
+	say("encode 85");
+	while (bytes) {
+		unsigned acc = 0;
+		int cnt;
+		for (cnt = 24; cnt >= 0; cnt -= 8) {
+			int ch = *data++;
+			acc |= ch << cnt;
+			if (--bytes == 0)
+				break;
+		}
+		say1(" %08x", acc);
+		for (cnt = 4; cnt >= 0; cnt--) {
+			int val = acc % 85;
+			acc /= 85;
+			buf[cnt] = en85[val];
+		}
+		buf += 5;
+	}
+	say("\n");
+
+	*buf = 0;
+}
+
+#ifdef DEBUG_85
+int main(int ac, char **av)
+{
+	char buf[1024];
+
+	if (!strcmp(av[1], "-e")) {
+		int len = strlen(av[2]);
+		encode_85(buf, av[2], len);
+		if (len <= 26) len = len + 'A' - 1;
+		else len = len + 'a' - 26 + 1;
+		printf("encoded: %c%s\n", len, buf);
+		return 0;
+	}
+	if (!strcmp(av[1], "-d")) {
+		int len = *av[2];
+		if ('A' <= len && len <= 'Z') len = len - 'A' + 1;
+		else len = len - 'a' + 26 + 1;
+		decode_85(buf, av[2]+1, len);
+		printf("decoded: %.*s\n", len, buf);
+		return 0;
+	}
+	if (!strcmp(av[1], "-t")) {
+		char t[4] = { -1,-1,-1,-1 };
+		encode_85(buf, t, 4);
+		printf("encoded: D%s\n", buf);
+		return 0;
+	}
+}
+#endif