node.js - 如何用代码实现一个小端的16进制字符串（无符号大整数）转化为10进制整数
如题，想要实现如下功能，入参可以是代表16进制的字符串或者一个buffer，是小端的
// return {@string}
function converHexStrToDecStrLittleEnd(strOrBuffer){
hexToDecLE(strOrBuffer)
}
//test case
assert( converHexStrToDecStrLittleEnd('a4fb02129a907c4a') === '5367323847320337316' )求 converHexStrToDecStrLittleEnd 这个函数怎么实现
直接用Buffer.from('a4fb02129a907c4a','hex').readUIntLE(0,8)只能得到5367323847320337000明显是溢出了
======最后结果如下========================================
/**
* A function for converting hex <-> dec w/o loss of precision.
*
* The problem is that parseInt("0x12345...") isn't precise enough to convert
* 64-bit integers correctly.
*
* Internally, this uses arrays to encode decimal digits starting with the least
* significant:
* 8 = [8]
* 16 = [6, 1]
* 1024 = [4, 2, 0, 1]
*/
// Adds two arrays for the given base (10 or 16), returning the result.
// This turns out to be the only "primitive" operation we need.
function add(x, y, base) {
var z = [];
var n = Math.max(x.length, y.length);
var carry = 0;
var i = 0;
while (i < n || carry) {
var xi = i < x.length ? x[i] : 0;
var yi = i < y.length ? y[i] : 0;
var zi = carry + xi + yi;
z.push(zi % base);
carry = Math.floor(zi / base);
i++;
}
return z;
}
// Returns a*x, where x is an array of decimal digits and a is an ordinary
// JavaScript number. base is the number base of the array x.
function multiplyByNumber(num, x, base) {
if (num < 0) return null;
if (num == 0) return [];
var result = [];
var power = x;
while (true) {
if (num & 1) {
result = add(result, power, base);
}
num = num >> 1;
if (num === 0) break;
power = add(power, power, base);
}
return result;
}
function parseToDigitsArray(str, base) {
var digits = str.split('');
var ary = [];
for (var i = digits.length - 1; i >= 0; i--) {
var n = parseInt(digits[i], base);
if (isNaN(n)) return null;
ary.push(n);
}
return ary;
}
function convertBase(str, fromBase, toBase) {
var digits = parseToDigitsArray(str, fromBase);
if (digits === null) return null;
var outArray = [];
var power = [1];
for (var i = 0; i < digits.length; i++) {
// invariant: at this point, fromBase^i = power
if (digits[i]) {
outArray = add(outArray, multiplyByNumber(digits[i], power, toBase), toBase);
}
power = multiplyByNumber(fromBase, power, toBase);
}
var out = '';
for (var i = outArray.length - 1; i >= 0; i--) {
out += outArray[i].toString(toBase);
}
return out;
}
function decToHex(decStr) {
var hex = convertBase(decStr, 10, 16);
return hex ? '0x' + hex : null;
}
function hexToDec(hexStr) {
if (hexStr.substring(0, 2) === '0x') hexStr = hexStr.substring(2);
hexStr = hexStr.toLowerCase();
return convertBase(hexStr, 16, 10);
}
function hexToDecLE(hexStr) {
var len = hexStr.length,arr = [];
for(var i=len;i>0;i-=2){
arr.push(hexStr.slice(i-2,i))
}
return hexToDec(arr.join(''));
}
hexToDecLE('a4fb02129a907c4a');
