java-round函數源碼

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public static long round(double a) {        long longBits = Double.doubleToRawLongBits(a);        long biasedExp = (longBits & DoubleConsts.EXP_BIT_MASK)                >> (DoubleConsts.SIGNIFICAND_WIDTH - 1);        long shift = (DoubleConsts.SIGNIFICAND_WIDTH - 2                + DoubleConsts.EXP_BIAS) - biasedExp;        if ((shift & -64) == 0) { // shift >= 0 && shift < 64            // a is a finite number such that pow(2,-64) <= ulp(a) < 1            long r = ((longBits & DoubleConsts.SIGNIF_BIT_MASK)                    | (DoubleConsts.SIGNIF_BIT_MASK + 1));            if (longBits < 0) {                r = -r;            }            // In the comments below each Java expression evaluates to the value            // the corresponding mathematical expression:            // (r) evaluates to a / ulp(a)            // (r >> shift) evaluates to floor(a * 2)            // ((r >> shift) + 1) evaluates to floor((a + 1/2) * 2)            // (((r >> shift) + 1) >> 1) evaluates to floor(a + 1/2)            return ((r >> shift) + 1) >> 1;        } else {            // a is either            // - a finite number with abs(a) < exp(2,DoubleConsts.SIGNIFICAND_WIDTH-64) < 1/2            // - a finite number with ulp(a) >= 1 and hence a is a mathematical integer            // - an infinity or NaN            return (long) a;        }    }

　　

java-round函數源碼