一、js 最大安全数字是 Math.pow(2,53) - 1,超出这个数字相加会出现精度丢失问题,可通过将数字转换为字符串操作的思路处理,如下:
let a = '123456444565456.889'
let b = '121231456.32'
function addTwo(a, b) {
if (a.length > b.length) {
let arr = Array(a.length - b.length).fill(0);
b = arr.join('') + b
} else if (a.length < b.length) {
let arr = Array(b.length - a.length).fill(0);
a = arr.join('') + a
}
a = a.split('').reverse();
b = b.split('').reverse();
let sign = 0;
let newVal = [];
for (let j = 0; j < a.length; j++) {
let val = a[j] / 1 + b[j] / 1 + sign;
if (val >= 10) {
sign = 1;
newVal.unshift(val % 10)
} else {
sign = 0;
newVal.unshift(val)
}
}
return sign && newVal.unshift(sign) && newVal.join('') || newVal.join('')
}
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function addTwo(a,b) {
let temp = 0
let res = ''
a = a.split('')
b = b.split('')
while(a.length || b.length || temp) {
temp += Number(a.pop() || 0) + Number(b.pop() || 0)
res = (temp%10) + res
temp = temp > 9
}
return res.replace(/^0+/g, '')
}
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二、当涉及到带有小数部分相加时,对上面方法进行一次封装,完整实现如下:
let a = '123456444565456.889'
let b = '121231456.32'
function addTwo(a = '0',b = '0', isHasDecimal=false) {
if (a.length > b.length) {
let arr = Array(a.length - b.length).fill(0);
b = isHasDecimal && (b + arr.join('')) || arr.join('') + b
} else if (a.length < b.length) {
let arr = Array(b.length - a.length).fill(0);
a = isHasDecimal && (a + arr.join('')) || arr.join('') + a
}
a = a.split('').reverse();
b = b.split('').reverse();
let sign = 0;
let newVal = [];
for (let j = 0; j < a.length; j++) {
let val = a[j] / 1 + b[j] / 1 + sign;
if (val >= 10) {
sign = 1;
newVal.unshift(val % 10)
} else {
sign = 0;
newVal.unshift(val)
}
}
return sign && newVal.unshift(sign) && newVal.join('') || newVal.join('')
}
function add(a,b) {
let num1 = String(a).split('.')
let num2 = String(b).split('.')
let intSum = addTwo(num1[0], num2[0])
let res = intSum
if (num1.length>1 || num2.length > 1) {
let decimalSum = addTwo(num1[1], num2[1], true)
if (decimalSum.length > (num1[1]||'0').length && decimalSum.length > (num2[1]||'0').length) {
intSum = addTwo(intSum, decimalSum[0])
decimalSum = decimalSum.slice(1)
res = `${intSum}.${decimalSum}`
} else {
res = `${intSum}.${decimalSum}`
}
}
return res
}
console.log(add(a, b))
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