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-rw-r--r--base85.c134
1 files changed, 134 insertions, 0 deletions
diff --git a/base85.c b/base85.c
new file mode 100644
index 0000000..b97f7f9
--- /dev/null
+++ b/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