Function Dragon4

numpy/core/src/multiarray/dragon4.c:1142–1576

* This is an implementation the Dragon4 algorithm to convert a binary number in * floating point format to a decimal number in string format. The function * returns the number of digits written to the output buffer and the output is * not NUL terminated. * * The floating point input value is (mantissa * 2^exponent). * * See the following papers for more information on the algorithm: * "Ho

 * Returns the number of digits written to the output buffer.
 */
static npy_uint32
Dragon4(BigInt *bigints, const npy_int32 exponent,
        const npy_uint32 mantissaBit, const npy_bool hasUnequalMargins,
        const DigitMode digitMode, const CutoffMode cutoffMode,
        npy_int32 cutoff_max, npy_int32 cutoff_min, char *pOutBuffer,
        npy_uint32 bufferSize, npy_int32 *pOutExponent)
{
    char *curDigit = pOutBuffer;

    /*
     * We compute values in integer format by rescaling as
     *   mantissa = scaledValue / scale
     *   marginLow = scaledMarginLow / scale
     *   marginHigh = scaledMarginHigh / scale
     * Here, marginLow and marginHigh represent 1/2 of the distance to the next
     * floating point value above/below the mantissa.
     *
     * scaledMarginHigh will point to scaledMarginLow in the case they must be
     * equal to each other, otherwise it will point to optionalMarginHigh.
     */
    BigInt *mantissa = &bigints[0];  /* the only initialized bigint */
    BigInt *scale = &bigints[1];
    BigInt *scaledValue = &bigints[2];
    BigInt *scaledMarginLow = &bigints[3];
    BigInt *scaledMarginHigh;
    BigInt *optionalMarginHigh = &bigints[4];

    BigInt *temp1 = &bigints[5];
    BigInt *temp2 = &bigints[6];

    const npy_float64 log10_2 = 0.30102999566398119521373889472449;
    npy_int32 digitExponent, hiBlock;
    npy_int32 cutoff_max_Exponent, cutoff_min_Exponent;
    npy_uint32 outputDigit;    /* current digit being output */
    npy_uint32 outputLen;
    npy_bool isEven = BigInt_IsEven(mantissa);
    npy_int32 cmp;

    /* values used to determine how to round */
    npy_bool low, high, roundDown;

    DEBUG_ASSERT(bufferSize > 0);

    /* if the mantissa is zero, the value is zero regardless of the exponent */
    if (BigInt_IsZero(mantissa)) {
        *curDigit = '0';
        *pOutExponent = 0;
        return 1;
    }

    BigInt_Copy(scaledValue, mantissa);

    if (hasUnequalMargins) {
        /* if we have no fractional component */
        if (exponent > 0) {
            /*
             * 1) Expand the input value by multiplying out the mantissa and
             *    exponent. This represents the input value in its whole number