js 版本

 function compare(p, q) {
  while (p[0] === '0') {
    p = p.substr(1);
  }
  while (q[0] === '0') {
    q = q.substr(1);
  }
  if (p.length > q.length) {
    return 1;
  } else if (p.length < q.length) {
    return -1;
  } else {
    let i = 0;
    let a, b;
    while (1) {
      a = parseInt(p.charAt(i));
      b = parseInt(q.charAt(i));
      if (a > b) {
        return 1;
      } else if (a < b) {
        return -1;
      } else if (i === p.length - 1) {
        return 0;
      }
      i++;
    }
  }
}
 
function divide(A, B) {
  let result = [];
  let max = 9;
  let point = 5;
  let fill = 0;
  if (B.length - A.length > 0) {
    point += fill = B.length - A.length;
  }
  for (let i = 0; i < point; i++) {
    A += '0';
  }
  let la = A.length;
  let lb = B.length;
 
  let b0 = parseInt(B.charAt(0));
  let Adb = A.substr(0, lb);
  A = A.substr(lb);
  let temp, r;
  for (let j = 0; j < la - lb + 1; j++) {
    while (Adb[0] === '0') {
      Adb = Adb.substr(1);
    }
    if (Adb.length === lb) {
      max = Math.ceil((parseInt(Adb.charAt(0)) + 1) / b0); // 不可能取到这个最大值,1<= max <= 10
    } else if (Adb.length > lb) {
      max = Math.ceil((parseInt(Adb.substr(0, 2)) + 1) / b0);
    } else {
      result.push(0);
      Adb += A[0];
      A = A.substr(1);
      continue;
    }
    for (let i = max - 1; i >= 0; i--) {
      if (i === 0) {
        result.push(0);
        Adb += A[0];
        A = A.substr(1);
        break;
      } else {
        temp = temp || multiply(B, i + '');
        r = compare(temp, Adb);
        if (r === 0 || r === -1) {
          result.push(i);
          if (r) {
            Adb = reduce(Adb, temp);
            Adb += A[0];
          } else {
            Adb = A[0];
          }
          A = A.substr(1);
          break;
        } else {
          temp = reduce(temp, B);
        }
      }
    }
    temp = 0;
  }
  for (let i = 0; i < fill; i++) {
    result.unshift('0');
  }
  result.splice(result.length - point, 0, '.');
 
  if (!result[0] && result[1] !== '.') {
    result.shift();
  }
 
  point = false;
  let position = result.indexOf('.');
 
  for (let i = position + 1; i < result.length; i++) {
    if (result[i]) {
      point = true;
      break;
    }
  }
  if (!point) {
    result.splice(position);
  }
 
  result = result.join('');
  return result;
}
 
function multiply(A, B) {
  let result = [];
  (A += ''), (B += '');
  const l = -4; // 以支持百万位精确运算，但速度减半
 
  let r1 = [],
    r2 = [];
  while (A !== '') {
    r1.unshift(parseInt(A.substr(l)));
    A = A.slice(0, l);
  }
  while (B !== '') {
    r2.unshift(parseInt(B.substr(l)));
    B = B.slice(0, l);
  }
  let index, value;
  for (let i = 0; i < r1.length; i++) {
    for (let j = 0; j < r2.length; j++) {
      value = 0;
      if (r1[i] && r2[j]) {
        value = r1[i] * r2[j];
      }
      index = i + j;
      if (result[index]) {
        result[index] += value;
      } else {
        result[index] = value;
      }
    }
  }
  for (let i = result.length - 1; i > 0; i--) {
    result[i] += '';
    if (result[i].length > -l) {
      result[i - 1] += parseInt(result[i].slice(0, l));
      result[i] = result[i].substr(l);
    }
    while (result[i].length < -l) {
      result[i] = '0' + result[i];
    }
  }
  if (result[0]) {
    result = result.join('');
  } else {
    result = '0';
  }
  return result;
}
 
function add(A, B) {
  let result = [];
  (A += ''), (B += '');
  const l = -15;
  while (A !== '' && B !== '') {
    result.unshift(parseInt(A.substr(l)) + parseInt(B.substr(l)));
    A = A.slice(0, l);
    B = B.slice(0, l);
  }
  A += B;
 
  for (let i = result.length - 1; i > 0; i--) {
    result[i] += '';
    if (result[i].length > -l) {
      result[i - 1] += 1;
      result[i] = result[i].substr(1);
    } else {
      while (result[i].length < -l) {
        result[i] = '0' + result[i];
      }
    }
  }
 
  while (A && (result[0] + '').length > -l) {
    result[0] = (result[0] + '').substr(1);
    result.unshift(parseInt(A.substr(l)) + 1);
    A = A.slice(0, l);
  }
 
  if (A) {
    while ((result[0] + '').length < -l) {
      result[0] = '0' + result[0];
    }
    result.unshift(A);
  }
 
  if (result[0]) {
    result = result.join('');
  } else {
    result = '0';
  }
 
  return result;
}
 
function reduce(A, B) {
  let result = [];
  (A += ''), (B += '');
  while (A[0] === '0') {
    A = A.substr(1);
  }
  while (B[0] === '0') {
    B = B.substr(1);
  }
  const l = -15;
  let N = '1';
  for (let i = 0; i < -l; i++) {
    N += '0';
  }
  N = parseInt(N);
  while (A !== '' && B !== '') {
    result.unshift(parseInt(A.substr(l)) - parseInt(B.substr(l)));
    A = A.slice(0, l);
    B = B.slice(0, l);
  }
  if (A !== '' || B !== '') {
    let s = B === '' ? 1 : -1;
    A += B;
    while (A !== '') {
      result.unshift(s * parseInt(A.substr(l)));
      A = A.slice(0, l);
    }
  }
  while (result.length !== 0 && result[0] === 0) {
    result.shift();
  }
  let s = '';
  if (result.length === 0) {
    result = 0;
  } else if (result[0] < 0) {
    s = '-';
    for (let i = result.length - 1; i > 0; i--) {
      if (result[i] > 0) {
        result[i] -= N;
        result[i - 1]++;
      }
      result[i] *= -1;
      result[i] += '';
      while (result[i].length < -l) {
        result[i] = '0' + result[i];
      }
    }
    result[0] *= -1;
  } else {
    for (let i = result.length - 1; i > 0; i--) {
      if (result[i] < 0) {
        result[i] += N;
        result[i - 1]--;
      }
      result[i] += '';
      while (result[i].length < -l) {
        result[i] = '0' + result[i];
      }
    }
  }
 
  if (result) {
    while ((result[0] = parseInt(result[0])) === 0) {
      result.shift();
    }
    result = s + result.join('');
  }
  return result;
}

php 版本

php中的bcmul()函数是一个内置函数，用于将两个任意精度的数字相乘。此函数接受两个任意精度的数字作为字符串，并在将结果缩放到指定精度后返回两个数字的乘法