From 7281e1b6ee4cdb3ec042f6ba7bfeace337f6a7da Mon Sep 17 00:00:00 2001
From: MelKori <mieldo@gmail.com>
Date: Sat, 20 Aug 2022 17:42:58 +0300
Subject: [PATCH] added Base58 implementation

---
 src-java/ai/z7/blockchain_misc/Base58.java | 96 ++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 src-java/ai/z7/blockchain_misc/Base58.java

diff --git a/src-java/ai/z7/blockchain_misc/Base58.java b/src-java/ai/z7/blockchain_misc/Base58.java
new file mode 100644
index 0000000..bf61a91
--- /dev/null
+++ b/src-java/ai/z7/blockchain_misc/Base58.java
@@ -0,0 +1,96 @@
+package ai.z7.blockchain_misc;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+public class Base58 {
+    public static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
+    private static final char ENCODED_ZERO = ALPHABET[0];
+    private static final int[] INDEXES = new int[128];
+
+    static {
+        Arrays.fill(INDEXES, -1);
+        for (int i = 0; i < ALPHABET.length; i++) {
+            INDEXES[ALPHABET[i]] = i;
+        }
+    }
+
+    public static String encode(byte[] input) {
+        if (input.length == 0) {
+            return "";
+        }
+        // Count leading zeros.
+        int zeros = 0;
+        while (zeros < input.length && input[zeros] == 0) {
+            ++zeros;
+        }
+        // Convert base-256 digits to base-58 digits (plus conversion to ASCII characters)
+        input = Arrays.copyOf(input, input.length); // since we modify it in-place
+        char[] encoded = new char[input.length * 2]; // upper bound
+        int outputStart = encoded.length;
+        for (int inputStart = zeros; inputStart < input.length; ) {
+            encoded[--outputStart] = ALPHABET[divmod(input, inputStart, 256, 58)];
+            if (input[inputStart] == 0) {
+                ++inputStart; // optimization - skip leading zeros
+            }
+        }
+        // Preserve exactly as many leading encoded zeros in output as there were leading zeros in input.
+        while (outputStart < encoded.length && encoded[outputStart] == ENCODED_ZERO) {
+            ++outputStart;
+        }
+        while (--zeros >= 0) {
+            encoded[--outputStart] = ENCODED_ZERO;
+        }
+        // Return encoded string (including encoded leading zeros).
+        return new String(encoded, outputStart, encoded.length - outputStart);
+    }
+
+    public static byte[] decode(String input) throws IOException {
+        if (input.length() == 0) {
+            return new byte[0];
+        }
+        // Convert the base58-encoded ASCII chars to a base58 byte sequence (base58 digits).
+        byte[] input58 = new byte[input.length()];
+        for (int i = 0; i < input.length(); ++i) {
+            char c = input.charAt(i);
+            int digit = c < 128 ? INDEXES[c] : -1;
+            if (digit < 0) {
+                throw new IOException();
+            }
+            input58[i] = (byte) digit;
+        }
+        // Count leading zeros.
+        int zeros = 0;
+        while (zeros < input58.length && input58[zeros] == 0) {
+            ++zeros;
+        }
+        // Convert base-58 digits to base-256 digits.
+        byte[] decoded = new byte[input.length()];
+        int outputStart = decoded.length;
+        for (int inputStart = zeros; inputStart < input58.length; ) {
+            decoded[--outputStart] = divmod(input58, inputStart, 58, 256);
+            if (input58[inputStart] == 0) {
+                ++inputStart; // optimization - skip leading zeros
+            }
+        }
+        // Ignore extra leading zeroes that were added during the calculation.
+        while (outputStart < decoded.length && decoded[outputStart] == 0) {
+            ++outputStart;
+        }
+        // Return decoded data (including original number of leading zeros).
+        return Arrays.copyOfRange(decoded, outputStart - zeros, decoded.length);
+    }
+
+    private static byte divmod(byte[] number, int firstDigit, int base, int divisor) {
+        // this is just long division which accounts for the base of the input digits
+        int remainder = 0;
+        for (int i = firstDigit; i < number.length; i++) {
+            int digit = (int) number[i] & 0xFF;
+            int temp = remainder * base + digit;
+            number[i] = (byte) (temp / divisor);
+            remainder = temp % divisor;
+        }
+        return (byte) remainder;
+    }
+}
+