Skip to content

Instantly share code, notes, and snippets.

@lqt0223
Created April 28, 2018 10:02
Show Gist options
  • Save lqt0223/3bcee9a93e00a2943ed5f85df52bf391 to your computer and use it in GitHub Desktop.
Save lqt0223/3bcee9a93e00a2943ed5f85df52bf391 to your computer and use it in GitHub Desktop.
35 binary adder
// a half-adder takes 2 binary bits as input, and return as result the sum and carry flag
function halfAdder(a, b) {
// the sum is 0 when two bits are the same (1 + 1 or 0 + 0)
var s = a ^ b
// the carry flag is set when 1 + 1
// the bitwise expression !(a ^ b) is for testing equality between a and b
var c = !(a ^ 1) && (!a ^ b)
return [c, s]
}
// a full-adder takes 2 binary bits and a carry flag as input,
// and return as result the sum and the carry flag after summation
function fullAdder(a, b, cin) {
var [c2, tsum] = halfAdder(b, cin)
var [c1, sum] = halfAdder(a, tsum)
var cout = c1 | c2
return [cout, sum]
}
// a full-adder can be use to add two numbers in 1 bit
// a sequence of full-adders in cascade can be use to add two numbers in N bits
function binaryAdder(addend, augend) {
addend = addend.split('').map((digit) => {
return parseInt(digit)
})
augend = augend.split('').map((digit) => {
return parseInt(digit)
})
return baHelper(addend, augend, 0, [])
}
function baHelper(addend, augend, cin, result) {
if (addend.length === 0 && augend.length === 0) {
result.unshift(cin)
return result.join('')
} else {
var a = addend.pop()
var b = augend.pop()
var [cout, sum] = fullAdder(a, b, cin)
result.unshift(sum)
return baHelper(addend, augend, cout, result)
}
}
// test:
// 0b10010010 + 0b10101010 = 0b10111111111 (binary)
// 146 + 170 = 316 (decimal)
var result = binaryAdder('10010010', '10101010')
console.log(result)
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment