浅析Java BigDecimal为什么可以不丢失精度

public class BigDecimal extends Number implements Comparable<BigDecimal> {
    // 该BigDecimal的未缩放值
    private final BigInteger intVal;
    // 精度，可以理解成小数点后的位数
    private final int scale;
    // BigDecimal中的十进制位数，如果位数未知，则为0(备用信息)
    private transient int precision;
    // Used to store the canonical string representation, if computed.
    // 这个我理解就是存实际的BigDecimal值
    private transient String stringCache;
    // 扩大成long型数值后的值
    private final transient long intCompact;
}

@Test
public void testBigDecimal() {
    BigDecimal bigDecimal1 = BigDecimal.valueOf(2.36);
    BigDecimal bigDecimal2 = BigDecimal.valueOf(3.5);
    BigDecimal resDecimal = bigDecimal1.add(bigDecimal2);
    System.out.println(resDecimal);
}

/**
 * Returns a BigDecimal whose value is (this + augend), 
 * and whose scale is max(this.scale(), augend.scale()).
 */
public BigDecimal add(BigDecimal augend) {
    if (this.intCompact != INFLATED) {
        if ((augend.intCompact != INFLATED)) {
            return add(this.intCompact, this.scale, augend.intCompact, augend.scale);
        } else {
            return add(this.intCompact, this.scale, augend.intVal, augend.scale);
        }
    } else {
        if ((augend.intCompact != INFLATED)) {
            return add(augend.intCompact, augend.scale, this.intVal, this.scale);
        } else {
            return add(this.intVal, this.scale, augend.intVal, augend.scale);
        }
    }
}

private static BigDecimal add(final long xs, int scale1, final long ys, int scale2) {
    long sdiff = (long) scale1 - scale2;
    if (sdiff == 0) {
        return add(xs, ys, scale1);
    } else if (sdiff < 0) {
        int raise = checkScale(xs,-sdiff);
        long scaledX = longMultiplyPowerTen(xs, raise);
        if (scaledX != INFLATED) {
            return add(scaledX, ys, scale2);
        } else {
            BigInteger bigsum = bigMultiplyPowerTen(xs,raise).add(ys);
            return ((xs^ys)>=0) ? // same sign test
                new BigDecimal(bigsum, INFLATED, scale2, 0)
                : valueOf(bigsum, scale2, 0);
        }
    } else {
        int raise = checkScale(ys,sdiff);
        long scaledY = longMultiplyPowerTen(ys, raise);
        if (scaledY != INFLATED) {
            return add(xs, scaledY, scale1);
        } else {
            BigInteger bigsum = bigMultiplyPowerTen(ys,raise).add(xs);
            return ((xs^ys)>=0) ?
                new BigDecimal(bigsum, INFLATED, scale1, 0)
                : valueOf(bigsum, scale1, 0);
        }
    }
}

private static BigDecimal add(long xs, long ys, int scale){
    long sum = add(xs, ys);
    if (sum!=INFLATED)
        return BigDecimal.valueOf(sum, scale);
    return new BigDecimal(BigInteger.valueOf(xs).add(ys), scale);
}