func (p prob) bound(r uint32) uint32 {
	return (r >> probbits) * uint32(p)
}
Computes the new bound for a given range using the probability value.
package lzma
const movebits = 5
const probbits = 11
const probInit prob = 1 << (probbits - 1)
type prob uint16
func (p *prob) dec() {
	*p -= *p >> movebits
}
func (p *prob) inc() {
	*p += ((1 << probbits) - *p) >> movebits
}