binary diff: further updates.

This updates the user interface and generated diff data format.

 * "diff --binary" is used to signal that we want an e-mailable
   binary patch.  It implies --full-index and -p.

 * "apply --allow-binary-replacement" acquired a short synonym
   "apply --binary".

 * After the "GIT binary patch\n" header line there is a token
   to record which binary patch mechanism was used, so that we
   can extend it later.  Currently there are two mechanisms
   defined: "literal" and "delta".  The former records the
   deflated postimage and the latter records the deflated delta
   from the preimage to postimage.

   For purely implementation convenience, I added the deflated
   length after these "literal/delta" tokens (otherwise the
   decoding side needs to guess and reallocate the buffer while
   inflating).  Improvement patches are very welcomed.

Signed-off-by: Junio C Hamano <junkio@cox.net>

base85.c

@@ -0,0 +1,134 @@
+#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, char *buffer, int len)
+{
+	prep_base85();
+
+	say2("decode 85 <%.*s>", len/4*5, buffer);
+	while (len) {
+		unsigned acc = 0;
+		int cnt;
+		for (cnt = 0; cnt < 5; cnt++, buffer++) {
+			int ch = *((unsigned char *)buffer);
+			int de = de85[ch];
+			if (!de)
+				return error("invalid base85 alphabet %c", ch);
+			de--;
+			if (cnt == 4) {
+				/*
+				 * 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 ||
+				    (0x03030303 == acc && de))
+					error("invalid base85 sequence %.5s",
+					      buffer-3);
+			}
+			acc = acc * 85 + de;
+			say1(" <%08x>", acc);
+		}
+		say1(" %08x", acc);
+		for (cnt = 0; cnt < 4 && len; cnt++, len--) {
+			*dst++ = (acc >> 24) & 0xff;
+			acc = acc << 8;
+		}
+	}
+	say("\n");
+
+	return 0;
+}
+
+void encode_85(char *buf, unsigned char *data, int bytes)
+{
+	prep_base85();
+
+	say("encode 85");
+	while (bytes) {
+		unsigned acc = 0;
+		int cnt;
+		for (cnt = 0; cnt < 4 && bytes; cnt++, bytes--) {
+			int ch = *data++;
+			acc |= ch << ((3-cnt)*8);
+		}
+		say1(" %08x", acc);
+		for (cnt = 0; cnt < 5; cnt++) {
+			int val = acc % 85;
+			acc /= 85;
+			buf[4-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