io.github.frogif.calculator.number.impl.NumberRoundingMode Maven / Gradle / Ivy
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support general calculate for rational number and integer number, and precision lossless.
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package io.github.frogif.calculator.number.impl;
import io.github.frogif.calculator.number.util.OutObject;
import io.github.frogif.calculator.number.util.StrUtils;
/**
* 舍入方式
*/
public enum NumberRoundingMode {
/**
* 向远离0的方向舍入
*/
UP(new RoundingPolicy(){
@Override
public int round(boolean positive, int current, int next, boolean discard) {
return discard ? 1 : 0;
}
@Override
public int extraDecBitCount() {
return 0;
}
}),
/**
* 向接近0的方向舍入
*/
DOWN(new RoundingPolicy(){
@Override
public int round(boolean positive, int current, int next, boolean discard) {
return 0;
}
@Override
public int extraDecBitCount() {
return 0;
}
}),
/**
* 向上取整
*/
CEILING(new RoundingPolicy(){
@Override
public int round(boolean positive, int current, int next, boolean discard) {
return (discard && positive) ? 1 : 0;
}
@Override
public int extraDecBitCount() {
return 0;
}
}),
/**
* 向下取整
*/
FLOOR(new RoundingPolicy(){
@Override
public int round(boolean positive, int current, int next, boolean discard) {
return (discard && !positive) ? 1 : 0;
}
@Override
public int extraDecBitCount() {
return 0;
}
}),
/**
* 四舍五入
*/
HALF_UP(new RoundingPolicy(){
@Override
public int round(boolean positive, int current, int next, boolean discard) {
return next > 4 ? 1 : 0;
}
@Override
public int extraDecBitCount() {
return 1;
}
}),
/**
* 五舍六入
*/
HALF_DOWN(new RoundingPolicy(){
@Override
public int round(boolean positive, int current, int next, boolean discard) {
return (next > 5 || (next == 5 && discard)) ? 1 : 0;
}
@Override
public int extraDecBitCount() {
return 1;
}
}),
/**
* 银行家舍入
* 1. 四舍六入
* 2. 五后非0, 进一
* 3. 五后为0:
* -- 五前为偶, 舍去
* -- 五前为奇, 进一
*/
HALF_EVEN(new RoundingPolicy(){
@Override
public int round(boolean positive, int current, int next, boolean discard) {
int n1 = next < 10 ? 0 : (next / 10);
int n2 = next % 10;
if(n1 < 5){
return 0;
}else if(n1 > 5){
return 1;
}else{
if(n2 > 0 || discard){
return 1;
}else{
return current % 2;
}
}
}
@Override
public int extraDecBitCount() {
return 2;
}
});
private final RoundingPolicy policy;
NumberRoundingMode(RoundingPolicy policy){
this.policy = policy;
}
/**
* 舍入
* @param positive 整个待舍入的数字是否是正数: true - 是, false - 否
* @param current 舍入之后, 保留的最后一位小数的当前值
* @param next 舍入时, 参与判断的数字
* @param discard 除去保留数字后, 是否存在多余的小数被丢弃
* @return 按照该策略执行舍入之后, 产生的进位
*/
private int round(boolean positive, int current, int next, boolean discard){
return policy.round(positive, current, next, discard);
}
/**
* 额外需要的十进制位个数
*/
public int extraDecBitCount(){
return policy.extraDecBitCount();
}
/**
* 舍入策略
*/
private interface RoundingPolicy{
/**
* 舍入
* @param positive 整个待舍入的数字是否是正数: true - 是, false - 否
* @param current 舍入之后, 保留的最后一位小数的当前值
* @param next 舍入时, 参与判断的数字
* @param discard 除去保留数字后, 是否存在多余的小数被丢弃
* @return 按照该策略执行舍入之后, 产生的进位
*/
int round(boolean positive, int current, int next, boolean discard);
/**
* 执行舍入时, @param next 对应10进制中的几位
* @return 返回需要的十进制位
*/
int extraDecBitCount();
}
private static final String[] SIGN_MARK_ARRAY = {"", "-"};
/**
* 对字符串数字进行舍入, 返回舍入后的结果
*/
public static String roundOff(String number, int scale, NumberRoundingMode roundingMode){
if(scale < 0){
throw new IllegalArgumentException("scale must be positive, but is " + scale);
}
OutObject discard = new OutObject<>();
number = normalizeNumberForRoundOff(number, scale, roundingMode, discard);
char[] chars = number.toCharArray();
// 判断正负
final int start = chars[0] == '-' ? 1 : 0;
/*
* 定位小数点位置, 如果不存在小数点, 虚出小数点位置
* 这里没有直接返回, 是因为即使不存在小数位, 也说不准roundingMode的行为会导致整数部分是否存在进位
*/
int len = chars.length;
int extraDecBitCount = roundingMode.extraDecBitCount();
// 获取需要执行舍入的位的前一位
int current = 0;
int edge = len - 1 - extraDecBitCount; // 舍入后, 保留部分的最大索引位置
int skip = 0;
if(chars[edge] == '.'){
edge--;
skip = 1;
}
current = chars[edge] - '0';
// 确定roundingMode执行舍入需要判断的数
int next = 0;
for(int i = 0; i < extraDecBitCount; i++){
int p = edge + skip + i + 1;
next = next * 10 + ((len > p) ? (chars[p] - '0') : 0);
}
int carry = roundingMode.round(start == 0, current, next, Boolean.TRUE.equals(discard.value)); // 执行舍入
// 执行舍入及进位
int i = edge;
boolean isZero = true; // 记录是否全为0, 如果全为0, 则符号位需要去掉
for(; i >= start && carry != 0; i--){
char ch = chars[i];
if(ch != '.'){
int c = ch - '0' + carry;
chars[i] = (char)(c % 10 + '0');
carry = c / 10;
isZero = isZero && c == 0;
}
}
if(carry > 0){
return SIGN_MARK_ARRAY[start] + carry + String.valueOf(chars, start, edge - start + 1);
}else{
for(; isZero && i >= start; i--){
char ch = chars[i];
isZero = ch == '0' || ch == '.';
}
if(isZero){
return String.valueOf(chars, start, edge - start + 1);
}else{
return String.valueOf(chars, 0, edge + 1);
}
}
}
/**
* 修整数字, 使其方便进行舍入
* 修整后的数字, 只存在舍入时需要的必要数字
*/
private static String normalizeNumberForRoundOff(String number, int scale, NumberRoundingMode roundingMode, OutObject discard){
int dotPos = number.indexOf('.');
int len = number.length();
int lackLen = (dotPos < 0 ? (scale + 1) : (scale - (len - dotPos - 1))) + roundingMode.extraDecBitCount();
discard.value = false;
if(lackLen > 0){ // 需要补位
if(dotPos < 0){
return StrUtils.rightFill(number + '.', '0', lackLen - 1);
}else{
return StrUtils.rightFill(number, '0', lackLen);
}
}else if(lackLen < 0){ // 需要截断
for(int i = len + lackLen; i < len; i++){
char ch = number.charAt(i);
if(ch != '0'){
discard.value = true;
break;
}
}
return number.substring(0, len + lackLen);
}else{ // 直接返回
return number;
}
}
}
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