Relevant issue: https://golang.org/issue/14102
On Tue, 22 Sep 2020 at 08:54, Nasir Hussain <nasirhussain...@gmail.com> wrote: > The Amazing Rob Pike :D > > On Tue, Sep 22, 2020 at 12:13 PM Rob Pike <r...@golang.org> wrote: > >> I'm not going to debug you program for you - you'll learn more doing it >> yourself, but I glanced at it and saw immediately that you're missing an >> easy optimization. Raising a number to an integer power can be done much >> faster by repeated squaring according to the bit pattern of the exponent. >> I'll leave that cryptic comment alone to let you puzzle it out yourself. >> (Don't look it up; it's much more fun to figure out.) >> >> -rob >> >> >> On Tue, Sep 22, 2020 at 3:11 AM Hau Phan <haupc....@gmail.com> wrote: >> >>> i can't find get n-th root in document of go big package so i decided to >>> do it myself using newton's method. i found a solution at >>> https://www.geeksforgeeks.org/n-th-root-number/ and start to implement >>> in go. but my code only work fine for base 2. other base result gone too >>> far from correct. >>> >>> Anyone could show me where am i wrong. >>> >>> Here's my code >>> >>> ```go >>> package main >>> >>> import ( >>> "fmt" >>> "math/big" >>> "math/rand" >>> ) >>> >>> // PowFloat return x^n >>> func PowFloat(x *big.Float, n int64) *big.Float { >>> result := new(big.Float).SetInt64(1) >>> for i := 0; i < int(n); i++ { >>> result.Mul(result, x) >>> } >>> return result >>> } >>> >>> // GetNthRoothFloat get nth root of a using newton's method >>> func GetNthRoothFloat(a *big.Float, n int64) *big.Float { >>> N := new(big.Float).SetInt64(n) >>> xPre := new(big.Float).SetInt64(int64(rand.Intn(10) + 1)) >>> eps := new(big.Float).SetFloat64(0.00000000001) >>> delX := new(big.Float).SetInt64(2147483647) >>> xK := new(big.Float).SetInt64(0) >>> >>> for delX.Cmp(eps) > 0 { >>> t1 := new(big.Float).Sub(N, new(big.Float).SetFloat64(1.0)) // t1 = n-1 >>> t1 = t1.Mul(t1, xPre) // t1 = >>> (N-1) * xPre >>> t2 := new(big.Float).Quo(a, PowFloat(xPre, n-1)) // t2 = a/( >>> xPre^(n-1) ) >>> t3 := new(big.Float).Add(t1, t2) // t3 = t1 + >>> t2 >>> xK.Quo(t3, N) >>> delX = new(big.Float).Sub(xK, xPre) >>> delX.Abs(delX) >>> xPre = xK.Copy(xK) >>> } >>> return xK >>> } >>> >>> func main() { >>> t := new(big.Float).SetInt64(64) >>> fmt.Println(GetNthRoothFloat(t, 3)) >>> } >>> ``` >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to golang-nuts+unsubscr...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/5a38a7fe-426b-4f94-905e-79b42dcaa611n%40googlegroups.com >>> <https://groups.google.com/d/msgid/golang-nuts/5a38a7fe-426b-4f94-905e-79b42dcaa611n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/CAOXNBZQrjBjT-dDEK1Atu7R32aT1mgTsSAYhXAF7hXmj35BjuQ%40mail.gmail.com >> <https://groups.google.com/d/msgid/golang-nuts/CAOXNBZQrjBjT-dDEK1Atu7R32aT1mgTsSAYhXAF7hXmj35BjuQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/CAG9C_MeG0P%3DSy5732WvW-EfsreSObQve%3DLsEUms%3DdWdRenvZ4Q%40mail.gmail.com > <https://groups.google.com/d/msgid/golang-nuts/CAG9C_MeG0P%3DSy5732WvW-EfsreSObQve%3DLsEUms%3DdWdRenvZ4Q%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAJhgachbaTaxkWv66ktuPz1RPSnAm7zgc1r0kqEb2T4hUWEt3A%40mail.gmail.com.
