Function Dragon4_PrintFloat_IEEE_binary64

numpy/core/src/multiarray/dragon4.c:2391–2476

* IEEE binary64 floating-point format * * sign: 1 bit * exponent: 11 bits * mantissa: 52 bits */

 * mantissa: 52 bits
 */
static npy_uint32
Dragon4_PrintFloat_IEEE_binary64(
        Dragon4_Scratch *scratch, npy_float64 *value, Dragon4_Options *opt)
{
    char *buffer = scratch->repr;
    const npy_uint32 bufferSize = sizeof(scratch->repr);
    BigInt *bigints = scratch->bigints;

    union
    {
        npy_float64 floatingPoint;
        npy_uint64 integer;
    } floatUnion;
    npy_uint32 floatExponent, floatSign;
    npy_uint64 floatMantissa;

    npy_uint64 mantissa;
    npy_int32 exponent;
    npy_uint32 mantissaBit;
    npy_bool hasUnequalMargins;
    char signbit = '\0';


    /* deconstruct the floating point value */
    floatUnion.floatingPoint = *value;
    floatMantissa = floatUnion.integer & bitmask_u64(52);
    floatExponent = (floatUnion.integer >> 52) & bitmask_u32(11);
    floatSign = floatUnion.integer >> 63;

    /* output the sign */
    if (floatSign != 0) {
        signbit = '-';
    }
    else if (opt->sign) {
        signbit = '+';
    }

    /* if this is a special value */
    if (floatExponent == bitmask_u32(11)) {
        return PrintInfNan(buffer, bufferSize, floatMantissa, 13, signbit);
    }
    /* else this is a number */

    /* factor the value into its parts */
    if (floatExponent != 0) {
        /*
         * normal
         * The floating point equation is:
         *  value = (1 + mantissa/2^52) * 2 ^ (exponent-1023)
         * We convert the integer equation by factoring a 2^52 out of the
         * exponent
         *  value = (1 + mantissa/2^52) * 2^52 * 2 ^ (exponent-1023-52)
         *  value = (2^52 + mantissa) * 2 ^ (exponent-1023-52)
         * Because of the implied 1 in front of the mantissa we have 53 bits of
         * precision.
         *   m = (2^52 + mantissa)
         *   e = (exponent-1023+1-53)
         */