snippets.md

Custom parseDouble

    CalculateAverage_bjhara

    double value = parseDouble(buffer, valueLength);


    public static double parseDouble(byte[] bytes, int len) {
        long value = 0;
        int exp = 0;
        boolean negative = false;
        int decimalPlaces = Integer.MIN_VALUE;
        int index = 0;
        int ch = bytes[index];
        if (ch == '-') {
            negative = true;
            ch = bytes[++index];
        }
        while (index < len) {
            if (ch >= '0' && ch <= '9') {
                while (value >= Long.MAX_VALUE / 10) {
                    value >>>= 1;
                    exp++;
                }
                value = value * 10 + (ch - '0');
                decimalPlaces++;

            }
            else if (ch == '.') {
                decimalPlaces = 0;
            }
            if (index == bytes.length - 1) {
                break;
            }
            else {
                ch = bytes[++index];
            }
        }
        return asDouble(value, exp, negative, decimalPlaces);
    }

    private static double asDouble(long value, int exp, boolean negative, int decimalPlaces) {
        if (decimalPlaces > 0 && value < Long.MAX_VALUE / 2) {
            if (value < Long.MAX_VALUE / (1L << 32)) {
                exp -= 32;
                value <<= 32;
            }
            if (value < Long.MAX_VALUE / (1L << 16)) {
                exp -= 16;
                value <<= 16;
            }
            if (value < Long.MAX_VALUE / (1L << 8)) {
                exp -= 8;
                value <<= 8;
            }
            if (value < Long.MAX_VALUE / (1L << 4)) {
                exp -= 4;
                value <<= 4;
            }
            if (value < Long.MAX_VALUE / (1L << 2)) {
                exp -= 2;
                value <<= 2;
            }
            if (value < Long.MAX_VALUE / (1L << 1)) {
                exp -= 1;
                value <<= 1;
            }
        }
        for (; decimalPlaces > 0; decimalPlaces--) {
            exp--;
            long mod = value % 5;
            value /= 5;
            int modDiv = 1;
            if (value < Long.MAX_VALUE / (1L << 4)) {
                exp -= 4;
                value <<= 4;
                modDiv <<= 4;
            }
            if (value < Long.MAX_VALUE / (1L << 2)) {
                exp -= 2;
                value <<= 2;
                modDiv <<= 2;
            }
            if (value < Long.MAX_VALUE / (1L << 1)) {
                exp -= 1;
                value <<= 1;
                modDiv <<= 1;
            }
            if (decimalPlaces > 1)
                value += modDiv * mod / 5;
            else
                value += (modDiv * mod + 4) / 5;
        }
        final double d = Math.scalb((double) value, exp);
        return negative ? -d : d;
    }