/*
* Simple program to find prime factorization of large numbers.
*
* I did this to see how Go compares to Python on this.
* It's not as bad as C,
* but it still feels like programming in assembly language,
* compared to Python. Among other things,
* there's no operator overloading
* and no way to apply existing algorithms (e.g. square root)
* to big.Ints.
*/
package main
import (
"os"
"fmt"
"math/big"
)
func rough_sqrt(z *big.Int) *big.Int {
n := z.BitLen()
half_n := n / 2
if n % 2 != 0 {
half_n++
}
result := big.NewInt(0)
result.Exp(big.NewInt(2), big.NewInt(int64(half_n)), nil)
return result
}
func main() {
number := os.Args[1]
fmt.Printf("%s:", number)
z := big.NewInt(0)
one := big.NewInt(1)
quo, rem := big.NewInt(0), big.NewInt(0)
z.SetString(number, 10)
max_factor := rough_sqrt(z)
for divisor := big.NewInt(2); divisor.Cmp(max_factor) < 0;
divisor.Add(divisor, one) {
for {
// Is there a way to do this division inside the
for-condition?
quo.QuoRem(z, divisor, rem)
if 0 != rem.Sign() {
break
}
fmt.Printf(" %s", divisor)
z.Set(quo)
max_factor = rough_sqrt(z)
}
}
if z.Cmp(big.NewInt(1)) != 0 {
fmt.Printf(" %s", z)
}
fmt.Printf("\n")
}
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