进位方法

jsp

1、四舍六入 基进偶不进

function fomatFloat(src, pos) {
    var numArray, resultSymbol = "";
    if (src < 0) {
        resultSymbol = "-";
    }
    if (pos == "") {
        pos = new Number(0);
    }
    src = src.toString().replace("-", "");
    if (src.indexOf('.') > 0) {
        numArray = src.split('.');
        if (numArray[1].length > pos) {
            var endStr, isCarry=false;
            if (numArray[1].length > parseFloat(pos) + 1) {
                endStr = numArray[1].substring(parseFloat(pos) + 1);
                for (var i = 0; i < endStr.length; i++) {
                    if (endStr[i] > 0) {
                        isCarry = true;
                        break;
                    }
                }
            }
            numArray[1] = numArray[1].substring(0, pos + 1);
            var endChar = numArray[1][pos];
            var newpoint = new Number("0." + numArray[1].substring(0, pos));
            if (endChar >= 5 && pos >= 0) {
                if (endChar > 5) {
                    if (pos == 0) {
                        numArray[1] = 1;
                    }
                    else {
                        numArray[1] = parseFloat(newpoint) + parseFloat(Math.pow(0.1, pos));
                    }
                }
                else if (endChar == 5) {
                    //5后面有有效数字，直接向前进一位
                    if (isCarry) {
                        numArray[1] = parseFloat(newpoint) + parseFloat(Math.pow(0.1, pos));
                        return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
                    }
                    if (pos == 0) {
                        if (numArray[0] % 2 != 0) {
                            numArray[1] = 1;
                        } else {
                            numArray[1] = 0;
                        }
                        return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
                    }
                    var preChar = numArray[1][pos - 1];
                    if (preChar % 2 == 0) {
                        numArray[1] = newpoint;
                    }
                    else {
                        numArray[1] = parseFloat(newpoint) + parseFloat(Math.pow(0.1, pos));
                    }
                }
                return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
            }
            else {
                numArray[1] = newpoint;
                return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
            }
        }
        return src;

    } else {
        return resultSymbol + src;
    }
    return src;
}
function PointFloat(src, pos) {
    return Math.round(src * Math.pow(10, pos)) / Math.pow(10, pos);
}

2、四舍五入

Math.round(value*1000)/1000

3.直接截取3位小数；不到则补零

function numFormat(value,num){
    var a, b, c, i;
  a = value.toString();
  b = a.indexOf(".");
  c = a.length;
  if (num == 0) {
      if (b != -1) {
          a = a.substring(0, b);
      }
  } else {//如果没有小数点
      if (b == -1) {
          a = a + ".";
          for (i = 1; i <= num; i++) {
              a = a + "0";
          }
      } else {//有小数点，超出位数自动截取，否则补0
          a = a.substring(0, b + num + 1);
          for (i = c; i <= b + num; i++) {
              a = a + "0";
          }
      }
  }
  return a;
}
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java中
1、四舍五入
doubl d = 0.0008;
String.format("%.3f", d);   //0.001