Custom base conversion (to and from)
Handy to store large numbers in a shorter notation. Doesn't work with negative numbers (for negative numbers you need to store an additional byte to indicate a positive or negative value, pass the absolute value).
And here are some tests:
private static final short BASE_40_RADIX = 40; private static final short BASE_40_BASE = 48; private static final String BASE_40_ZERO = "0"; public static long fromBase40(char[] cs) { return fromBase(cs, BASE_40_BASE, BASE_40_RADIX); } public static char[] toBase40(final long i) { return toBase(i, BASE_40_BASE, BASE_40_RADIX, BASE_40_ZERO); } private static final short BASE_75_RADIX = 75; private static final short BASE_75_BASE = 48; private static final String BASE_75_ZERO = "0"; public static long fromBase75(char[] cs) { return fromBase(cs, BASE_75_BASE, BASE_75_RADIX); } public static char[] toBase75(final long i) { return toBase(i, BASE_75_BASE, BASE_75_RADIX, BASE_75_ZERO); } private static final short BASE_90_RADIX = 90; private static final short BASE_90_BASE = 33; private static final String BASE_90_ZERO = "!"; public static long fromBase90(char[] cs) { return fromBase(cs, BASE_90_BASE, BASE_90_RADIX); } public static char[] toBase90(final long i) { return toBase(i, BASE_90_BASE, BASE_90_RADIX, BASE_90_ZERO); } private static char[] toBase(final long i, final short base, final short radix, String nullCharacter) { long value = i; if (value == 0) { return nullCharacter.toCharArray(); } String result = ""; while (value > 0) { long mod = value % radix; value -= mod; if (value > 0) value /= radix; result = (char)(mod + base) + result; } return result.toCharArray(); } private static long fromBase(char[] cs, final short base, final short radix) { long value = 0; for (int i = cs.length - 1; i >= 0; i--) { int digit = ((int)cs[i]) - base; if (digit < 0 || digit >= radix) { throw new IllegalArgumentException("Invalid Base" + radix + " character: " + cs[i]); } long digitBase = (long)Math.pow(radix, (cs.length - 1) - i); value = (digit * digitBase) + value; } return value; }
And here are some tests:
public void testFromBase40() { assertEquals(2559999, NumberUtils.fromBase40("WWWW".toCharArray())); assertEquals(1117580, NumberUtils.fromBase40("ABCD".toCharArray())); assertEquals(0, NumberUtils.fromBase40("0".toCharArray())); assertEquals(1, NumberUtils.fromBase40("1".toCharArray())); assertEquals(40, NumberUtils.fromBase40("10".toCharArray())); assertEquals(80, NumberUtils.fromBase40("20".toCharArray())); assertEquals(41, NumberUtils.fromBase40("11".toCharArray())); assertEquals(81, NumberUtils.fromBase40("21".toCharArray())); assertEquals(81, NumberUtils.fromBase40("0021".toCharArray())); assertEquals(3061560805L, NumberUtils.fromBase40("MSTSD5".toCharArray())); } public void testToBase40() { assertEquals("0", new String(NumberUtils.toBase40(0))); assertEquals("1", new String(NumberUtils.toBase40(1))); assertEquals("10", new String(NumberUtils.toBase40(40))); assertEquals("20", new String(NumberUtils.toBase40(80))); assertEquals("11", new String(NumberUtils.toBase40(41))); assertEquals("21", new String(NumberUtils.toBase40(81))); assertEquals("ABCD", new String(NumberUtils.toBase40(1117580))); assertEquals("WWWW", new String(NumberUtils.toBase40(2559999))); assertEquals("MSTSD5", new String(NumberUtils.toBase40(3061560805L))); } public void testToBase90() throws Exception { assertEquals("#Q&Y.`QY#", new String(NumberUtils.toBase90(10908158098650842L))); } public void testFromBase90() throws Exception { assertEquals(10908158098650842L, NumberUtils.fromBase90("#Q&Y.`QY#".toCharArray())); }
