rand.go

package main

import (
	. "github.com/ktye/wg/module"
)

func rnd() int32 {
	r := rand_
	r ^= (r << 13)
	r ^= (r >> 17)
	r ^= (r << 5)
	rand_ = r
	return r
}
func roll(x K) K { // ?x (atom) ?n(uniform 0..1) ?-n(normal) ?z(binormal)
	xt := tp(x)
	xp := int32(x)
	if xt == it {
		if xp > 0 {
			return kx(72, x) // .rf uniform
		} else {
			r := kx(80, Ki((1+-xp)/2))
			SetI32(int32(r)-12, -xp)
			return ti(Ft, int32(r)) // normal
		}
	}
	if xt == zt {
		dx(x)
		return kx(80, Ki(int32(F64floor(F64(xp))))) //.rz binormal
	}
	trap() //type
	return 0
}
func deal(x, y K) K { // x?y (x atom) n?n(with replacement) -n?n(without) n?L (-#L)?L shuffle
	yt := tp(y)
	if yt > 16 {
		return In(x, y)
	}
	if tp(x) != it {
		trap() //type
	}
	xp := int32(x)
	if yt == ct {
		return Add(Kc(97), Flr(deal(x, Ki(int32(y)-96))))
	}
	if yt == st {
		return Ech(17, l2(Ks(0), deal(x, Fst(cs(y))))) // `$'x?*$y
	}
	if yt != it {
		trap() //type
	}
	yp := int32(y)
	if xp > 0 {
		return randI(yp, xp) // n?m
	}
	// todo n<<m
	return ntake(-xp, shuffle(seq(yp), -xp)) //-n?m (no duplicates)
}
func randi(n int32) int32 {
	v := uint32(rnd())
	prod := uint64(v) * uint64(n)
	low := uint32(prod)
	if low < uint32(n) {
		thresh := uint32(-n) % uint32(n)
		for low < thresh {
			v = uint32(rnd())
			prod = uint64(v) * uint64(n)
			low = uint32(prod)
		}
	}
	return int32(prod >> 32)
}
func randI(i, n int32) K {
	r := mk(It, n)
	rp := int32(r)
	e := ep(r)
	if i == 0 {
		for rp < e {
			SetI32(rp, rnd())
			rp += 4
		}
	} else {
		for rp < e {
			SetI32(rp, randi(i))
			rp += 4
		}
	}
	return r
}
func shuffle(r K, m int32) K { // I, inplace
	rp := int32(r)
	n := nn(r)
	m = mini(n-1, m)
	for i := int32(0); i < m; i++ {
		j := rp + 4*randi(n-i)
		t := I32(rp)
		SetI32(rp, I32(j))
		SetI32(j, t)
		rp += 4
	}
	return r
}