Integer division with remainder in JavaScript

Question

In JavaScript  how do I get    The whole number of times a given integer goes into another  The remainder

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I m no expert in bitwise operators  but here s another way to get the whole number   var num      a   b     This will work properly for negative numbers as well  while Math floor   will round in the wrong direction   This seems correct as well   var num    a   b   gt  gt  0

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var remainder   x   y  return  x - remainder    y

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Alex Moore-Niemi s comment as an answer   For Rubyists here from Google in search of divmod  you can implement it as such    function divmod x  y      var div   Math trunc x y     var rem   x   y    return  div  rem       Result       2  33

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Calculating number of pages may be done in one step  Math ceil x y

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I normally use   const quotient     a - a   b    b  const remainder   a   b    It s probably not the most elegant  but it works

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ES6 introduces the new Math trunc method  This allows to fix  MarkElliot s answer to make it work for negative numbers too   var div   Math trunc y x   var rem   y   x    Note that Math methods have the advantage over bitwise operators that they work with numbers over 231

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You can use ternary to decide how to handle positive and negative integer values as well   var myInt    y  gt  0    Math floor y x    Math floor y x    1   If the number is a positive  all is fine  If the number is a negative  it will add 1 because of how Math floor handles negatives

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const idivmod    a  b    gt   a b  0  a b    there is also a proposal working on it Modulus and Additional Integer Math

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JavaScript calculates right the floor of negative numbers and the remainder of non-integer numbers  following the mathematical definitions for them   FLOOR is defined as  the largest integer number smaller than the parameter   thus    positive numbers  FLOOR X  integer part of X  negative numbers  FLOOR X  integer part of X minus 1  because it must be SMALLER than the parameter  i e   more negative     REMAINDER is defined as the  left over  of a division  Euclidean arithmetic   When the dividend is not an integer  the quotient is usually also not an integer  i e   there is no remainder  but if the quotient is forced to be an integer  and that s what happens when someone tries to get the remainder or modulus of a floating-point number   there will be a non-integer  left over   obviously   JavaScript does calculate everything as expected  so the programmer must be careful to ask the proper questions  and people should be careful to answer what is asked   Yarin s first question was NOT  what is the integer division of X by Y   but  instead   the WHOLE number of times a given integer GOES INTO another   For positive numbers  the answer is the same for both  but not for negative numbers  because the integer division  dividend by divisor  will be -1 smaller than the times a number  divisor   goes into  another  dividend   In other words  FLOOR will return the correct answer for an integer division of a negative number  but Yarin didn t ask that   gammax answered correctly  that code works as asked by Yarin  On the other hand  Samuel is wrong  he didn t do the maths  I guess  or he would have seen that it does work  also  he didn t say what was the divisor of his example  but I hope it was 3    Remainder   X   Y   -100   3   -1  GoesInto    X - Remainder    Y    -100 - -1    3   -99   3   -33  By the way  I tested the code on Firefox 27 0 1  it worked as expected  with positive and negative numbers and also with non-integer values  both for dividend and divisor  Example   -100 34   3 57  GoesInto   -28  Remainder   -0 3800000000000079  Yes  I noticed  there is a precision problem there  but I didn t had time to check it  I don t know if it s a problem with Firefox  Windows 7 or with my CPU s FPU   For Yarin s question  though  which only involves integers  the gammax s code works perfectly

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You can use the function parseInt to get a truncated result   parseInt a b    To get a remainder  use mod operator   a b   parseInt have some pitfalls with strings  to avoid use radix parameter with base 10  parseInt  09   10    In some cases the string representation of the number can be a scientific notation  in this case  parseInt will produce a wrong result   parseInt 100000000000000000000000000000000  10     1e 32   This call will produce 1 as result

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Math floor operation  returns the rounded down value of the operation   Example of 1st question   var x   5  var y   10 4  var z   Math floor x   y    console log z     Console      15   Example of 2nd question   var x   14  var y   5  var z   Math floor x y    console log x     Console      4

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I did some speed tests on Firefox   -100 3                -33 33     0 3663 millisec Math floor -100 3     -34        0 5016 millisec    -100 3             -33        0 3619 millisec  -100 3 gt  gt 0            -33        0 3632 millisec  -100 3 0             -33        0 3856 millisec  -100- -100 3   3     -33        0 3591 millisec     a -100  b 3    a b                   -33 33     0 4863 millisec Math floor a b        -34        0 6019 millisec    a b                -33        0 5148 millisec  a b gt  gt 0               -33        0 5048 millisec  a b 0                -33        0 5078 millisec  a- a b   b           -33        0 6649 millisec   The above is based on 10 million trials for each   Conclusion  Use  a b gt  gt 0   or     a b   or  a b 0   to achieve about 20  gain in efficiency  Also keep in mind that they are all inconsistent with Math floor  when a b lt 0  amp  amp  a b  0

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function integerDivison dividend  divisor                this Division    dividend divisor          this Quotient   Math floor dividend divisor            this Remainder   dividend divisor          this calculate       gt               return  Value this Division Quotient this Quotient Remainder this Remainder                                var divide   new integerDivison 5 2     console log divide Quotient         to get Quotient of two value    console log divide division        to get Floating division of two value    console log divide Remainder        to get Remainder of two value    console log divide calculate        to get object containing all the values

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For some number y and some divisor x compute the quotient  quotient  and remainder  remainder  as   var quotient   Math floor y x   var remainder   y   x

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Here is a way to do this   Personally I would not do it this way  but thought it was a fun way to do it for an example   x000D   x000D  function intDivide numerator  denominator      return parseInt  numerator denominator  toString   split      0       let x   intDivide 4 5   let y   intDivide 5 5   let z   intDivide 6 5   console log x   console log y   console log z   x000D   x000D   x000D

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This will always truncate towards zero  Not sure if it is too late  but here it goes   function intdiv dividend  divisor         divisor   divisor - divisor   1      if  divisor    0  throw new Error  division by zero        dividend   dividend - dividend   1      var rem   dividend   divisor      return            remainder  rem           quotient   dividend - rem    divisor

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If you are just dividing with powers of two  you can use bitwise operators   export function divideBy2 num      return  num  gt  gt  1  num  amp  1      export function divideBy4 num      return  num  gt  gt  2  num  amp  3      export function divideBy8 num      return  num  gt  gt  3  num  amp  7        The first is the quotient  the second the remainder

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If you need to calculate the remainder for very large integers  which the JS runtime cannot represent as such  any integer greater than 2 32 is represented as a float and so it loses precision   you need to do some trick   This is especially important for checking many case of check digits which are present in many instances of our daily life  bank account numbers  credit cards        First of all you need your number as a string  otherwise you have already lost precision and the remainder does not make sense    str    123456789123456789123456789    You now need to split your string in smaller parts  small enough so the concatenation of any remainder and a piece of string can fit in 9 digits   digits   9 - String divisor  length   Prepare a regular expression to split the string  splitter   new RegExp    1   digits          digits          g     For instance  if digits is 7  the regexp is     1 7       7      g   It matches a nonempty substring of maximum length 7  which is followed          is a positive lookahead  by a number of characters that is multiple of 7  The  g  is to make the expression run through all string  not stopping at first match   Now convert each part to integer  and calculate the remainders by reduce  adding back the previous remainder - or 0 - multiplied by the correct power of 10    reducer    rem  piece    gt   rem   Math pow 10  digits    piece    divisor   This will work because of the  subtraction  remainder algorithm   n mod d    n - kd  mod d   which allows to replace any  initial part  of the decimal representation of a number with its remainder  without affecting the final remainder   The final code would look like   function remainder num  div      const digits   9 - String div  length    const splitter   new RegExp    1   digits          digits          g      const mult   Math pow 10  digits     const reducer    rem  piece    gt   rem   mult   piece    div     return str match splitter  map Number  reduce reducer  0

[javascript] Integer division with remainder in JavaScript?

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