[TOC] # big.Int 在官方的 math/big 包中，Int 類型定義如下： ~~~ // An Int represents a signed multi-precision integer. // The zero value for an Int represents the value 0. type Int struct { neg bool // sign abs nat // absolute value of the integer } ~~~ 生成 Int 類型的方法為 NewInt()，如下： ~~~ // NewInt allocates and returns a new Int set to x. func NewInt(x int64) *Int { return new(Int).SetInt64(x) } ~~~ 可見，NewInt() 函數只對 int64 有效，其他類型必須先轉成 int64 才行。 但是，官方還提供了許多 Set 函數，可以方便的把其他類型的整形存入 Int ，因此，我們可以先 new(int) 然后再調用 Set 函數。 ~~~ // SetInt64 sets z to x and returns z. func (z *Int) SetInt64(x int64) *Int { neg := false if x < 0 { neg = true x = -x } z.abs = z.abs.setUint64(uint64(x)) z.neg = neg return z } ? // SetUint64 sets z to x and returns z. func (z *Int) SetUint64(x uint64) *Int { z.abs = z.abs.setUint64(x) z.neg = false return z } ? // Set sets z to x and returns z. func (z *Int) Set(x *Int) *Int { if z != x { z.abs = z.abs.set(x.abs) z.neg = x.neg } return z } ~~~ 用法示例 ~~~ func main() { big1 := new(big.Int).SetUint64(uint64(1000)) fmt.Println("big1 is: ", big1) big2 := big1.Uint64() fmt.Println("big2 is: ", big2) } ~~~ 除了上述的 Set 函數，big 庫還提供了一個 SetString() 函數，可以指定進制數，比如二進制、十進制或者十六進制等！ ~~~ // SetString sets z to the value of s, interpreted in the given base, // and returns z and a boolean indicating success. The entire string // (not just a prefix) must be valid for success. If SetString fails, // the value of z is undefined but the returned value is nil. // // The base argument must be 0 or a value between 2 and MaxBase. If the base // is 0, the string prefix determines the actual conversion base. A prefix of // ``0x'' or ``0X'' selects base 16; the ``0'' prefix selects base 8, and a // ``0b'' or ``0B'' prefix selects base 2. Otherwise the selected base is 10. // func (z *Int) SetString(s string, base int) (*Int, bool) { r := strings.NewReader(s) if _, _, err := z.scan(r, base); err != nil { return nil, false } // entire string must have been consumed if _, err := r.ReadByte(); err != io.EOF { return nil, false } return z, true // err == io.EOF => scan consumed all of s } ~~~ 用法示例 ~~~ func main() { big1 := new(big.Int).SetString("1000", 10) fmt.Println("big1 is: ", big1) big2 := big1.Uint64() fmt.Println("big2 is: ", big2) } ~~~ uint64, int64 等普通類型與 big.Int 類型的轉換 如上，直接調用 big 庫提供的 Int64(), Uint64() 等函數就可以進行轉換。 Int 對象上的運算函數 ~~~ Mul(im, in) Add(ip, im) Div(ip, io) ~~~ ~~~ import ( "fmt" "math" "math/big" ) func main() { // Here are some calculations with bigInts: im := big.NewInt(math.MaxInt64) in := im io := big.NewInt(1956) ip := big.NewInt(1) ip.Mul(im, in).Add(ip, im).Div(ip, io) fmt.Printf("Big Int: %v\n", ip) // Here are some calculations with bigInts: rm := big.NewRat(math.MaxInt64, 1956) rn := big.NewRat(-1956, math.MaxInt64) ro := big.NewRat(19, 56) rp := big.NewRat(1111, 2222) rq := big.NewRat(1, 1) rq.Mul(rm, rn).Add(rq, ro).Mul(rq, rp) fmt.Printf("Big Rat: %v\n", rq) } /* Output: Big Int: 43492122561469640008497075573153004 Big Rat: -37/112 */ ~~~ 輸出結果： ~~~ Big Int: 43492122561469640008497075573153004 Big Rat: -37/112 ~~~