我正在寻找可以处理大量数字的 Crockford Base32 的 Java 实现。这是我正在使用的数字类型的示例：
0003019140802085400304608040952
我见过几个使用编码 Long 并解码为 long 的实现，但这比 Long 的最大值大得多。
我找到了这个实现，但它似乎给出了奇怪的结果： https://gist.githubusercontent.com/markov/5206312/raw/ba5ec8ff1ef894ac889d2d1fad359d51d91e8ab9/CrockfordBase32.java
上面的数字应该编码为 2E1BZQDAGC4G6TTENZR，但这个实现并没有给我任何接近的东西。
【问题讨论】：
这是 Base32 的一般实现，其中包含 Crockford 字符集的实现。它同时具有 format 和 parse 方法，应该是免费的。
/**
* Parse and format base 32 numbers.
*
* Some of this may apply to almost any format but there's much that won't
* such as allowing both uppercase and lowercase forms of each digit.
*
* See: http://en.wikipedia.org/wiki/Base32
*/
public class Base32 {
// The character sets.
// Like Hex but up to V
private static final String base32HexCharacterSet = "0123456789ABCDEFGHIJKLMNOPQRSTUV";
// Common alternative - avoids O/0, i/1 etc.
private static final String base32CharacterSet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
// Avoids vowels (and therefore real words)
private static final String zBase32CharacterSet = "YBNDRFG8EJKMCPQXOT1UWISZA345H769";
// Avoids o/0 confusion.
private static final String crockfordCharacterSet = "0123456789ABCDEFGHJKMNPQRSTVWXYZ";
// Known/published formats.
// Uses the BigInteger formatter.
public static final Base32 ordinary = new Base32();
// A lot like the BigInteger formatter - but using my mechanism.
public static final Base32 base32Hex = new Base32(base32HexCharacterSet);
// The RFC 4648 Base32.
public static final Base32 base32 = new Base32(base32CharacterSet);
// Supposedly more natural than RFC 4648.
public static final Base32 zBase32 = new Base32(zBase32CharacterSet);
// Much like normal but recodes some similar looking characters to the same character.
public static final Base32 crockfords = new Base32(crockfordCharacterSet, "O0", "o0", "L1", "l1", "I1", "i1");
// Invalid character.
private static final int Invalid = -1;
// The radix - fixed at 32 bits.
private static final int radix = 32;
// The bits per digit - could use (int) (Math.log(radix) / Math.log(2))
private static final int bitsPerDigit = 5;
// The bits per byte.
private static final int bitsPerByte = 8;
// Translation table for each code.
private final char[] formatTable;
// Translation table for each character.
private final int[] parseTable;
// Constructor - Probably should be private but why restrict the user.
public Base32() {
// Empty tables makes us match BigInteger format so no formatting/parsing is required.
formatTable = null;
parseTable = null;
}
// Constructor with character set and optional extras :).
protected Base32(String characterSet, String... extras) {
// Check the character set against the radix.
if (characterSet.length() != radix) {
throw new NumberFormatException("Invalid character set. Must be " + radix + " long");
}
// Build the format table.
formatTable = buildFormatTable(characterSet);
// And the parse table.
parseTable = buildParseTable(characterSet, extras);
}
// Build a format table from the character set.
private char[] buildFormatTable(String characterSet) {
// Start clear.
char[] table = new char[radix];
// Put each character from the character set in.
for (int i = 0; i < radix; i++) {
table[i] = characterSet.charAt(i);
}
return table;
}
private int[] buildParseTable(String characterSet, String... extras) {
// Handle all characters up to and including 'z'.
int[] table = new int['z' + 1];
// By default invalid character.
Arrays.fill(table, Invalid);
// Lowercase and uppercase versions.
String lc = characterSet.toLowerCase();
String uc = characterSet.toUpperCase();
// Walk through the character set.
for (int i = 0; i < radix; i++) {
char l = lc.charAt(i);
char u = uc.charAt(i);
// Something wrong if we've already filled this one in.
if (table[l] == Invalid && table[u] == Invalid) {
// Put both lowercase and uppercase forms in the table.
table[l] = i;
table[u] = i;
} else {
// Failed.
throw new NumberFormatException("Invalid character set - duplicate found at position " + i);
}
}
// Add extras.
for (String pair : extras) {
// Each Must be length 2.
if (pair.length() == 2) {
// From
int f = pair.charAt(1);
// To
int t = pair.charAt(0);
// Something wrong if we've already filled this one in or we are copying from one that is not filled in.
if (table[f] != Invalid && table[t] == Invalid) {
// EG "O0" means a capital oh should be treated as a zero.
table[t] = table[f];
} else {
// Failed.
throw new NumberFormatException("Invalid character set extra - copying from " + f + " to " + t);
}
} else {
// Failed.
throw new NumberFormatException("Invalid extra \"" + pair + "\" - should be 2 characters wide.");
}
}
return table;
}
// Format a BigInteger.
public String format(BigInteger n) {
// Get its raw Radix32 string - in uppercase.
String formatted = n.toString(radix).toUpperCase();
// Further formatting through the format table?
if (formatTable != null) {
// Translate it.
char[] translated = new char[formatted.length()];
for (int i = 0; i < formatted.length(); i++) {
// Use Character.digit to decode the digit value.
int d = Character.digit(formatted.charAt(i), radix);
// Translate to that.
translated[i] = formatTable[d];
}
formatted = new String(translated);
}
return formatted;
}
// Parse a string.
public BigInteger parse(String s) {
BigInteger big;
// Pass it through the parse table if present.
if (parseTable != null) {
// Digits in the number.
int digits = s.length();
// Total bits (+1 to avoid sign bit).
int bits = digits * bitsPerDigit + 1;
// Number of bytes.
int bytes = (bits + bitsPerByte - 1) / bitsPerByte;
// Bias bits to slide to the right to get the bottom bit rightmost (+1 to avoid sign bit).
int bias = (bytes * bitsPerByte) - bits + 1;
// Make my array.
byte[] parsed = new byte[bytes];
// Walk the string.
for (int i = 0, bit = bias; i < digits; i++, bit += bitsPerDigit) {
// The character.
char c = s.charAt(i);
// Must be in the parse table.
if (c < parseTable.length) {
// Roll in each digit value into the correct bits.
int n = parseTable[c];
// Special cases.
switch (n) {
case 0:
// Nothing to do.
break;
default:
// How far to shift it to line up with "bit"
int shift = (bitsPerByte - bitsPerDigit - (bit % bitsPerByte));
// Sorry about the name.
int bite = bit / bitsPerByte;
// +ve shift is left into this byte.
if (shift >= 0) {
// Slide left only.
parsed[bite] |= n << shift;
} else {
// Split across this byte and the next.
parsed[bite] |= n >>> -shift;
// Slide right.
parsed[bite + 1] |= n << (bitsPerByte + shift);
}
break;
case Invalid:
// Must be mapped to something.
throw new NumberFormatException("Invalid character '" + c + "' at position " + i);
}
} else {
// Failed.
throw new NumberFormatException("Invalid character '" + c + "' at position " + i);
}
}
// Grow the biginteger out of the byte array.
big = new BigInteger(parsed);
} else {
// No parsing - it's ordinary.
big = new BigInteger(s, radix);
}
return big;
}
// Check a string.
public boolean good(String s) {
boolean good = true;
// Check each character.
for (int i = 0; i < s.length() && good; i++) {
// The character.
char c = s.charAt(i);
if (parseTable != null) {
if (c < parseTable.length) {
// Must be a valid character.
good = parseTable[c] != Invalid;
} else {
// Out of range of the parse table.
good = false;
}
} else {
// Use Character.digit - returns -1 if not valid.
good = Character.digit(c, radix) != -1;
}
}
return good;
}
public static void main(String args[]) {
Test.main(args);
}
}
class Test {
// For testing only.
private static Random r = new Random();
/*
* A 95 bit number fits in a 12 byte binary with a bit to spare (sign bit).
* A 95 bit number formats in base 32 to 19 digits exactly.
*
* Other numbers of this type:
* 15 bits 2 bytes 3 digits
* 55 bits 7 bytes 11 digits
* 95 bits 12 bytes 19 digits
* 135 bits 17 bytes 27 digits
* 175 bits 22 bytes 35 digits
* 215 bits 27 bytes 43 digits
* 255 bits 32 bytes 51 digits
*/
private static final int testBits = 95;
public static void main(String args[]) {
test(new BigInteger("10"));
test(new BigInteger("32"));
test(new BigInteger("100"));
BigInteger big = BigInteger.valueOf(0);
for (int i = 0; i < 1000; i++, big = big.add(BigInteger.ONE)) {
test(big);
}
for (int i = 0; i < 1000; i++) {
test(new BigInteger(testBits, r));
}
testCrockfords();
}
private static void test(BigInteger i) {
test(i, Base32.ordinary, "Ordinary");
test(i, Base32.base32Hex, "Base32Hex");
test(i, Base32.base32, "Base32");
test(i, Base32.crockfords, "Crockfords");
test(i, Base32.zBase32, "ZBase32");
}
private static void test(BigInteger i, Base32 f, String name) {
test(i, f, f.format(i), name);
}
private static void test(BigInteger i, Base32 f, String formatted, String name) {
BigInteger parsed = f.parse(formatted);
boolean ok = parsed.equals(i) && f.good(formatted);
//if (!ok) {
// For debug - so we can trace the issue.
BigInteger reParsed = f.parse(formatted);
boolean good = f.good(formatted);
System.out.println(i + " = " + f.format(i) + " in " + name + (ok ? " Ok" : " BAD!"));
if (!ok) {
System.out.println(reParsed + " != " + i);
}
//}
}
private static void testCrockfords() {
/// Crockford uses extras.
BigInteger anztenney = new BigInteger("0003019140802085400304608040952");
String formatted = Base32.crockfords.format(anztenney);
test(anztenney, Base32.crockfords, formatted, "Crockfords Test");
for (int i = 0; i < 100; i++) {
BigInteger b = BigInteger.valueOf(i);
formatted = Base32.crockfords.format(b);
test(b, Base32.crockfords, formatted, "Crockfords Test");
}
for (int i = 0; i < 1000; i++) {
BigInteger b = new BigInteger(testBits, r);
formatted = Base32.crockfords.format(b)
.replace('0', 'O')
.replace('1', 'l');
test(b, Base32.crockfords, formatted, "Crockfords Test");
}
}
}
注意：请彻底测试 - 这从未被认真使用过，因此可能存在错误。
测试确实输出了这一行：
3019140802085400304608040952 = 2E1BZQDAGC4G6TTENZR in Crockfords Test Ok
所以您的电话号码似乎翻译正确。
【讨论】：
radix=30，并尝试设置bitsPerDigit=(int) (Math.log(radix) / Math.log(2))，但运气不佳。
test(BigInteger("-1")) 将产生 ArrayIndexOutOfBoundsException
使用@OldCurmudgeon 的答案（这是我提出的问题的正确答案），我进行了一些修改，以允许从/到 base10 的任何基本编码/解码。这不是为性能而构建的，而是为功能而构建的。
import java.math.BigInteger;
import java.util.Arrays;
public abstract class BaseXEncoder {
// Invalid character.
private static final int Invalid = -1;
// x in baseX encoding
private int radix = 32;
// Translation table for each code.
private final char[] formatTable;
// Translation table for each character.
private final int[] parseTable;
// Constructor with character set and optional extras :).
protected BaseXEncoder(int radix, String characterSet, String... extras) {
this.radix = radix;
// Check the character set against the radix.
if (characterSet.length() != radix) {
throw new NumberFormatException("Invalid character set. Must be " + radix + " long");
}
// Build the format table.
formatTable = buildFormatTable(characterSet);
// And the parse table.
parseTable = buildParseTable(characterSet, extras);
}
public String encode(String numberValue) {
return encodeBigInt(new BigInteger(numberValue));
}
public String decode(String encoded) {
return decodeBigInt(encoded).toString();
}
// Format a BigInteger.
public String encodeBigInt(BigInteger n) {
// Get its raw Radix32 string - in uppercase.
String formatted = n.toString(radix).toUpperCase();
// Further formatting through the format table?
if (formatTable != null) {
// Translate it.
char[] translated = new char[formatted.length()];
for (int i = 0; i < formatted.length(); i++) {
// Use Character.digit to decode the digit value.
int d = Character.digit(formatted.charAt(i), radix);
// Translate to that.
translated[i] = formatTable[d];
}
formatted = new String(translated);
}
return formatted;
}
// Parse a string.
public BigInteger decodeBigInt(String encoded) {
BigInteger decoded = BigInteger.ZERO;
// Pass it through the parse table if present.
if (parseTable != null) {
BigInteger RADIX = new BigInteger(Integer.toString(radix));
// Digits in the number.
int digits = encoded.length();
// Walk the string.
for (int i = 0; i < digits; i++) {
// The character.
char c = encoded.charAt(i);
// Must be in the parse table.
if (c < parseTable.length) {
// Roll in each digit value into the correct bits.
int n = parseTable[c];
// Special cases.
switch (n) {
case Invalid:
// Must be mapped to something.
throw new NumberFormatException("Invalid character '" + c + "' at position " + i);
default:
if(i==0) {//First character, do something special
decoded = new BigInteger(Integer.toString(n));
} else {
decoded = RADIX.multiply(decoded).add(new BigInteger(Integer.toString(n)));
}
break;
}
} else {
// Failed.
throw new NumberFormatException("Invalid character '" + c + "' at position " + i);
}
}
} else {
// No parsing - it's ordinary.
decoded = new BigInteger(encoded, radix);
}
return decoded;
}
// Check a string.
public boolean good(String s) {
boolean good = true;
// Check each character.
for (int i = 0; i < s.length() && good; i++) {
// The character.
char c = s.charAt(i);
if (parseTable != null) {
if (c < parseTable.length) {
// Must be a valid character.
good = parseTable[c] != Invalid;
} else {
// Out of range of the parse table.
good = false;
}
} else {
// Use Character.digit - returns -1 if not valid.
good = Character.digit(c, radix) != -1;
}
}
return good;
}
// Build a format table from the character set.
private char[] buildFormatTable(String characterSet) {
// Start clear.
char[] table = new char[radix];
// Put each character from the character set in.
for (int i = 0; i < radix; i++) {
table[i] = characterSet.charAt(i);
}
return table;
}
private int[] buildParseTable(String characterSet, String... extras) {
// Handle all characters up to and including 'z'.
int[] table = new int['z' + 1];
// By default invalid character.
Arrays.fill(table, Invalid);
// Lowercase and uppercase versions.
String lc = characterSet.toLowerCase();
String uc = characterSet.toUpperCase();
// Walk through the character set.
for (int i = 0; i < radix; i++) {
char l = lc.charAt(i);
char u = uc.charAt(i);
// Something wrong if we've already filled this one in.
if (table[l] == Invalid && table[u] == Invalid) {
// Put both lowercase and uppercase forms in the table.
table[l] = i;
table[u] = i;
} else {
// Failed.
throw new NumberFormatException("Invalid character set - duplicate found at position " + i);
}
}
// Add extras.
for (String pair : extras) {
// Each Must be length 2.
if (pair.length() == 2) {
// From
int f = pair.charAt(1);
// To
int t = pair.charAt(0);
// Something wrong if we've already filled this one in or we are copying from one that is not filled in.
if (table[f] != Invalid && table[t] == Invalid) {
// EG "O0" means a capital oh should be treated as a zero.
table[t] = table[f];
} else {
// Failed.
throw new NumberFormatException("Invalid character set extra - copying from " + f + " to " + t);
}
} else {
// Failed.
throw new NumberFormatException("Invalid extra \"" + pair + "\" - should be 2 characters wide.");
}
}
return table;
}
}
【讨论】：