javascript - what is the result of 'x modulo y'? -

citing ecmascript spec section 5.2:

the notation “x modulo y” (y must finite , nonzero) computes value k of same sign y (or zero) such abs(k) < abs(y) , x−k = q × y integer q.

so if y positive, result k of 'x modulo y' positive regardless of sign of x.

and if understanding right, toint32(-1) equals toint32(1)?

the modulo operation defined mathematical modulo operation:

mathematical operations such addition, subtraction, negation, multiplication, division, , mathematical functions defined later in clause should understood computing exact mathematical results on mathematical real numbers, not include infinities , not include negative 0 distinguished positive zero.

your question:

toint32(-1) equals toint32(1)

well, no:

let posint sign(number) * floor(abs(number)).

posint = sign(-1) * floor(abs(-1)) = -1; 

let int32bit posint modulo 2³²; is, finite integer value k of number type positive sign , less 2³² in magnitude such mathematical difference of posint , k mathematically integer multiple of 2³².

int32bit = posint mod 4294967296 = -1 mod 4294967296 = 4294967295 

(wolfram alpha link mathematical result)

if int32bit greater or equal 2³¹, return int32bit − 2³², otherwise return int32bit.

because 4294967295 >= 2147483648, return 4294967295 - 4294967296, i.e. -1.

if run same steps toint32(1), 1. don't have same result.