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// SPDX-License-Identifier: BSD-2-Clause
// SPDX-FileCopyrightText: Copyright (c) 2025 Runxi Yu <https://runxiyu.org>
package main
import (
"bytes"
"crypto/sha256"
"encoding/base64"
"encoding/binary"
"fmt"
"os"
"runtime"
"strconv"
)
func validateBitZeros(bs []byte, n int) bool {
q := n / 8
r := n % 8
if !bytes.Equal(bs[:q], make([]byte, q)) {
return false
}
if r != 0 && (bs[q]&(0xFF<<(8-r)) != 0) {
return false
}
return true
}
func main() {
if len(os.Args) < 3 {
fmt.Fprintln(os.Stderr, "usage: program <base64 input> <difficulty>")
os.Exit(1)
}
decoded, err := base64.StdEncoding.DecodeString(os.Args[1])
if err != nil {
fmt.Fprintln(os.Stderr, "invalid base64:", err)
os.Exit(1)
}
difficulty, err := strconv.Atoi(os.Args[2])
if err != nil {
fmt.Fprintln(os.Stderr, "invalid difficulty:", err)
os.Exit(1)
}
numWorkers := runtime.NumCPU()
result := make(chan uint64)
for i := 0; i < numWorkers; i++ {
go func(start, step int) {
var nextVal uint64 = uint64(start)
buf := append(decoded, make([]byte, 8)...)
for {
binary.LittleEndian.PutUint64(buf[len(buf)-8:], nextVal)
h := sha256.Sum256(buf)
if validateBitZeros(h[:], difficulty) {
result <- nextVal
return
}
nextVal = (nextVal + uint64(step)) & 0xFFFFFFFFFFFFFFFF
if nextVal == uint64(start) {
fmt.Fprintln(os.Stderr, "overflow")
os.Exit(1)
}
}
}(i, numWorkers)
}
found := <-result
out := make([]byte, 8)
binary.LittleEndian.PutUint64(out, found)
fmt.Println(base64.StdEncoding.EncodeToString(out))
}
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