static String _toRadixStringUnsigned()

in lib/src/int64.dart [725:799]

• 39 lines of code
• 7 McCabe index (conditional complexity)

  static String _toRadixStringUnsigned(
      int radix, int d0, int d1, int d2, String sign) {
    if (d0 == 0 && d1 == 0 && d2 == 0) return '0';

    // Rearrange components into five components where all but the most
    // significant are 10 bits wide.
    //
    //     d4, d3, d4, d1, d0:  24 + 10 + 10 + 10 + 10 bits
    //
    // The choice of 10 bits allows a remainder of 20 bits to be scaled by 10
    // bits and added during division while keeping all intermediate values
    // within 30 bits (unsigned small integer range for 32 bit implementations
    // of Dart VM and V8).
    //
    //     6  6         5         4         3         2         1
    //     3210987654321098765432109876543210987654321098765432109876543210
    //     [--------d2--------][---------d1---------][---------d0---------]
    //  -->
    //     [----------d4----------][---d3---][---d2---][---d1---][---d0---]

    int d4 = (d2 << 4) | (d1 >> 18);
    int d3 = (d1 >> 8) & 0x3ff;
    d2 = ((d1 << 2) | (d0 >> 20)) & 0x3ff;
    d1 = (d0 >> 10) & 0x3ff;
    d0 = d0 & 0x3ff;

    int fatRadix = _fatRadixTable[radix];

    // Generate chunks of digits.  In radix 10, generate 6 digits per chunk.
    //
    // This loop generates at most 3 chunks, so we store the chunks in locals
    // rather than a list.  We are trying to generate digits 20 bits at a time
    // until we have only 30 bits left.  20 + 20 + 30 > 64 would imply that we
    // need only two chunks, but radix values 17-19 and 33-36 generate only 15
    // or 16 bits per iteration, so sometimes the third chunk is needed.

    String chunk1 = '', chunk2 = '', chunk3 = '';

    while (!(d4 == 0 && d3 == 0)) {
      int q = d4 ~/ fatRadix;
      int r = d4 - q * fatRadix;
      d4 = q;
      d3 += r << 10;

      q = d3 ~/ fatRadix;
      r = d3 - q * fatRadix;
      d3 = q;
      d2 += r << 10;

      q = d2 ~/ fatRadix;
      r = d2 - q * fatRadix;
      d2 = q;
      d1 += r << 10;

      q = d1 ~/ fatRadix;
      r = d1 - q * fatRadix;
      d1 = q;
      d0 += r << 10;

      q = d0 ~/ fatRadix;
      r = d0 - q * fatRadix;
      d0 = q;

      assert(chunk3 == '');
      chunk3 = chunk2;
      chunk2 = chunk1;
      // Adding [fatRadix] Forces an extra digit which we discard to get a fixed
      // width.  E.g.  (1000000 + 123) -> "1000123" -> "000123".  An alternative
      // would be to pad to the left with zeroes.
      chunk1 = (fatRadix + r).toRadixString(radix).substring(1);
    }
    int residue = (d2 << 20) + (d1 << 10) + d0;
    String leadingDigits = residue == 0 ? '' : residue.toRadixString(radix);
    return '$sign$leadingDigits$chunk1$chunk2$chunk3';
  }