StringUtil.java

/*
 * Copyright (C) ${year} Omry Yadan <${email}>
 * All rights reserved.
 *
 * See https://github.com/omry/banana/blob/master/BSD-LICENSE for licensing information
 */
package net.yadan.utils;

public class StringUtil {

  static char min_value[] = "-2147483648".toCharArray();

  public static int toChars(int number, char chars[]) {
    if (number == Integer.MIN_VALUE) {
      System.arraycopy(min_value, 0, chars, 0, min_value.length);
      return min_value.length;
    }
    int size = (number < 0) ? stringSize(-number) + 1 : stringSize(number);
    getChars(number, size, chars);
    return size;
  }

  /**
   * All possible chars for representing a number as a String
   */
  final static char[] digits = { '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' };

  final static char[] DigitTens = { '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '1', '1',
      '1', '1', '1', '1', '1', '1', '1', '1', '2', '2', '2', '2', '2', '2', '2', '2', '2', '2',
      '3', '3', '3', '3', '3', '3', '3', '3', '3', '3', '4', '4', '4', '4', '4', '4', '4', '4',
      '4', '4', '5', '5', '5', '5', '5', '5', '5', '5', '5', '5', '6', '6', '6', '6', '6', '6',
      '6', '6', '6', '6', '7', '7', '7', '7', '7', '7', '7', '7', '7', '7', '8', '8', '8', '8',
      '8', '8', '8', '8', '8', '8', '9', '9', '9', '9', '9', '9', '9', '9', '9', '9', };

  final static char[] DigitOnes = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1',
      '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
      '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7',
      '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5',
      '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '1', '2', '3',
      '4', '5', '6', '7', '8', '9', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', };

  /**
   * Places characters representing the integer i into the character array buf.
   * The characters are placed into the buffer backwards starting with the least
   * significant digit at the specified index (exclusive), and working backwards
   * from there.
   *
   * Will fail if i == Integer.MIN_VALUE
   */
  static void getChars(int i, int index, char[] buf) {
    int q, r;
    int charPos = index;
    char sign = 0;

    if (i < 0) {
      sign = '-';
      i = -i;
    }

    // Generate two digits per iteration
    while (i >= 65536) {
      q = i / 100;
      // really: r = i - (q * 100);
      r = i - ((q << 6) + (q << 5) + (q << 2));
      i = q;
      buf[--charPos] = DigitOnes[r];
      buf[--charPos] = DigitTens[r];
    }

    // Fall thru to fast mode for smaller numbers
    // assert(i <= 65536, i);
    for (;;) {
      q = (i * 52429) >>> (16 + 3);
      r = i - ((q << 3) + (q << 1)); // r = i-(q*10) ...
      buf[--charPos] = digits[r];
      i = q;
      if (i == 0)
        break;
    }
    if (sign != 0) {
      buf[--charPos] = sign;
    }
  }

  final static int[] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999, 99999999, 999999999,
      Integer.MAX_VALUE };

  // Requires positive x
  static int stringSize(int x) {
    for (int i = 0;; i++)
      if (x <= sizeTable[i])
        return i + 1;
  }
}