utils.go

package sllb

import (
	"math"
)

func zeros(registers []uint8) float64 {
	var z float64
	for _, val := range registers {
		if val == 0 {
			z++
		}
	}
	return z
}

func zerosSince(regs []*reg, since uint64) float64 {
	var z float64
	for _, reg := range regs {
		if reg.get(since) == 0 {
			z++
		}
	}
	return z
}

func beta(ez float64) float64 {
	zl := math.Log(ez + 1)
	return -0.370393911*ez +
		0.070471823*zl +
		0.17393686*math.Pow(zl, 2) +
		0.16339839*math.Pow(zl, 3) +
		-0.09237745*math.Pow(zl, 4) +
		0.03738027*math.Pow(zl, 5) +
		-0.005384159*math.Pow(zl, 6) +
		0.00042419*math.Pow(zl, 7)
}

// Calculate the position of the leftmost 1-bit.
func rho(val uint64, max uint8) (r uint8) {
	for val&0x8000000000000000 == 0 && r < max-1 {
		val <<= 1
		r++
	}
	return r + 1
}

func alpha(m float64) float64 {
	switch m {
	case 16:
		return 0.673
	case 32:
		return 0.697
	case 64:
		return 0.709
	}
	return 0.7213 / (1 + 1.079/m)
}

func regSumSince(regs []*reg, since uint64) float64 {
	sum := 0.0
	for _, reg := range regs {
		val := reg.get(since)
		sum += 1.0 / math.Pow(2.0, float64(val))
	}
	return sum
}