galois field 256 logic

exp(512)/log(256) available.

define

1. declare this.exp, this.log

this.exp=new Uint8Array(512)
this.log=new Uint8Array(256)

2. loop

for(let i=0,a=1;i<0xff;i++,a<<=1)

3. set a, exp, log

this.log[this.exp[i]=this.exp[0xff+i]=0xff<a?a^=v:a]=i