Method d2d

core/src/main/java/io/questdb/std/RyuDouble.java:424–609

Converts a decoded IEEE 754 double to its shortest decimal representation. @param ieeeMantissa the 52-bit mantissa (without implicit leading 1) @param ieeeExponent the biased 11-bit exponent (0-2046; 0 means subnormal) @param e10Out single-element array; receives the decimal exponent e10

(long ieeeMantissa, int ieeeExponent, int[] e10Out)

     * @return the decimal significand as a positive long (1-17 digits)
     */
    static long d2d(long ieeeMantissa, int ieeeExponent, int[] e10Out) {
        int e2;
        long m2;
        if (ieeeExponent == 0) {
            // Subnormal: no implicit leading 1, exponent is 1 (not 0)
            e2 = 1 - 1023 - 52;
            m2 = ieeeMantissa;
        } else {
            e2 = ieeeExponent - 1023 - 52;
            m2 = ieeeMantissa | (1L << 52);
        }

        // Fast path for small integers: if the value is an exact integer in [1, 2^53),
        // return it directly. This avoids the 4x-scaling issue in the main Ryu path.
        if (e2 >= -52 && e2 <= 0) {
            long mask = (1L << -e2) - 1;
            if ((m2 & mask) == 0) {
                long mantissa = m2 >>> -e2;
                int exp = 0;
                // Strip trailing decimal zeros
                while (mantissa > 0) {
                    long q = mantissa / 10;
                    long r = mantissa - 10 * q;
                    if (r != 0) {
                        break;
                    }
                    mantissa = q;
                    exp++;
                }
                e10Out[0] = exp;
                return mantissa;
            }
        }

        // Subtract 2 from e2 to account for the 4x scaling (mv = 4*m2 below).
        // This ensures mv * 2^e2 == m2 * 2^(e2_original), so the decimal
        // conversion produces the correct (non-4x) significand.
        e2 -= 2;

        boolean acceptBounds = (m2 & 1) == 0;

        // Step 2: Determine the interval of valid decimal representations.
        long mv = 4 * m2;
        long mp = 4 * m2 + 2;
        int mmShift = (ieeeMantissa != 0 || ieeeExponent <= 1) ? 1 : 0;
        long mm = 4 * m2 - 1 - mmShift;

        // Step 3: Convert to a decimal power base using 128-bit arithmetic.
        long vr, vp, vm;
        int e10;
        boolean vmIsTrailingZeros = false;
        boolean vrIsTrailingZeros = false;

        if (e2 >= 0) {
            int q = Math.max(0, ((e2 * 78913) >>> 18) - 1);
            e10 = q;
            int k = DOUBLE_POW5_INV_BITCOUNT + pow5bits(q) - 1;
            int i = -e2 + q + k;