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Removed hard-coded constant in sortition.go. #3558

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Merged
tsachiherman merged 5 commits into from
Feb 4, 2022
Merged

Removed hard-coded constant in sortition.go. #3558

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77c0965
Removed hard-coded constant in `sortition.go`.
Olshansk Feb 3, 2022
d27eabd
Remove the +1
Olshansk Feb 3, 2022
9c41c54
Create a local variable rather than recompute it each time
Olshansk Feb 3, 2022
b31c833
Moved maxFloat generation into an init function
Olshansk Feb 4, 2022
1645da6
Replace the *2 and with
Olshansk Feb 4, 2022
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26 changes: 19 additions & 7 deletions data/committee/sortition/sortition.go
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Original file line number Diff line number Diff line change
Expand Up @@ -22,12 +22,19 @@ package sortition
// #include <stdlib.h>
// #include "sortition.h"
import "C"

import (
"fmt"
"math/big"
"strings"

"github.com/algorand/go-algorand/crypto"
)

const precision = uint(8 * (crypto.DigestSize + 1))

var maxFloat *big.Float

// Select runs the sortition function and returns the number of time the key was selected
func Select(money uint64, totalMoney uint64, expectedSize float64, vrfOutput crypto.Digest) uint64 {
binomialN := float64(money)
Expand All @@ -36,18 +43,23 @@ func Select(money uint64, totalMoney uint64, expectedSize float64, vrfOutput cry
t := &big.Int{}
t.SetBytes(vrfOutput[:])

precision := uint(8 * (len(vrfOutput) + 1))
max, b, err := big.ParseFloat("0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 0, precision, big.ToNearestEven)
if b != 16 || err != nil {
panic("failed to parse big float constant in sortition")
}

h := big.Float{}
h.SetPrec(precision)
h.SetInt(t)

ratio := big.Float{}
cratio, _ := ratio.Quo(&h, max).Float64()
cratio, _ := ratio.Quo(&h, maxFloat).Float64()

return uint64(C.sortition_binomial_cdf_walk(C.double(binomialN), C.double(binomialP), C.double(cratio), C.uint64_t(money)))
}

func init() {
var b int
var err error
maxFloatString := fmt.Sprintf("0x%s", strings.Repeat("ff", crypto.DigestSize))
maxFloat, b, err = big.ParseFloat(maxFloatString, 0, precision, big.ToNearestEven)
if b != 16 || err != nil {
err = fmt.Errorf("failed to parse big float constant in sortition : %w", err)
panic(err)
}
}