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module.exports = basic = {}
// Handle bases up to base 36
basic.abedecary = "0123456789abcdefghijklmnopqrstuvwxyz"
// Validate that a string s represents a number in base b
basic.validate = function (s, b) {
return (base.validate_base(b) && base.validate_digits(s, b))
}
// Validate that a string does not contain numerals
// foreign to a particular base.
basic.validate_digits = function(s, b) {
var A = basic.abedecary.substr(0, b)
var re = new RegExp ( "[^" + A + "]" )
return !! re.match(s)
}
// Validate that a base is valid.
basic.validate_base = function(b){
return (b !== 0 && b !== 1 && b !== -1 && (Math.abs(b) % 2) === 0)
}
// Convert a string s representing a number in base b
// to an integer. Assumes s is big-endian.
basic.toNumber = function (s, b) {
if (! basic.validate(s,b)) {
return NaN
}
var n = 0
s = s.reverse()
for (var i = 0, len = s.length; i < len; i++) {
n += parseInt(s[i]) * Math.pow(b, i)
}
return n
}
// Convert an integer n to a string representing that
// integer in base b, big-endian.
basic.toString = function (n, b) {
if (! basic.validate_base(b)) {
throw new Error ("invalid base")
}
var s = ""
var dividend, residual
while (n) {
remainder = basic.mod(n, b)
n = Math.floor(n/b)
if (remainder) {
n += 1
}
s += basic.abedecary[n]
}
return s
}
// Compute the residual of N mod M
// Handle negative N and M correctly
basic.mod = function (n,m){
m = Math.abs(m)
return n-(m * Math.floor(n/m))
}
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