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revocation: switch to tadge's bit-shifting to figure out log2 instead of using math

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This commit is contained in:
Olaoluwa Osuntokun
2015-12-23 12:12:53 -06:00
parent a4762b818f
commit 868ac0aca0
1 changed files with 4 additions and 5 deletions
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9
revocation/shachain.go
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@ -5,7 +5,6 @@ import (
"crypto/rand" "crypto/rand"
"crypto/sha256" "crypto/sha256"
"fmt" "fmt"
"math"
"sync" "sync"
"github.com/btcsuite/btcd/wire" "github.com/btcsuite/btcd/wire"
@ -71,11 +70,11 @@ func derive(from, to uint64, startingHash [32]byte) [32]byte {
nextHash := startingHash nextHash := startingHash
numBranches := from ^ to numBranches := from ^ to
toDerive := uint64(math.Log2(float64(numBranches))) // uh.....
// math? floats? nahhh! :) bit-flipp-y way to do it: // The number of branches we need to derive is log2(numBranches)
for toDerive = 0; numBranches>>toDerive > 0; toDerive++ { toDerive := 0
for ; numBranches>>uint(toDerive) > 0; toDerive++ {
} }
// ^^^this rounds up instead of down, may be off by 1?
toDerive-- // needed? toDerive-- // needed?
for i := int(toDerive - 1); i >= 0; i-- { for i := int(toDerive - 1); i >= 0; i-- {