// 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 类型的方法为 NewInt(),如下所示:
// NewInt allocates and returns a new Int set to x. func NewInt(x int64) *Int { return new(Int).SetInt64(x) }
注意:NewInt() 函数只对 int64 有效,其他类型必须先转成 int64 才行。
Go语言中还提供了许多 Set 函数,可以方便的把其他类型的整形存入 Int ,因此,我们可以先 new(int) 然后再调用 Set 函数,Set 函数有如下几种:// SetInt64 函数将 z 转换为 x 并返回 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 函数将 z 转换为 x 并返回 z。 func (z *Int) SetUint64(x uint64) *Int { z.abs = z.abs.setUint64(x) z.neg = false return z } // Set 函数将 z 转换为 x 并返回 z。 func (z *Int) Set(x *Int) *Int { if z != x { z.abs = z.abs.set(x.abs) z.neg = x.neg } return z }示例代码如下所示:
package main import ( "fmt" "math/big" ) func main() { big1 := new(big.Int).SetUint64(uint64(1000)) fmt.Println("big1 is: ", big1) big2 := big1.Uint64() fmt.Println("big2 is: ", big2) }运行结果如下:
big1 is: 1000
big2 is: 1000
// 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 }示例代码如下所示:
package main import ( "fmt" "math/big" ) func main() { big1, _ := new(big.Int).SetString("1000", 10) fmt.Println("big1 is: ", big1) big2 := big1.Uint64() fmt.Println("big2 is: ", big2) }运行结果如下:
big1 is: 1000
big2 is: 1000
func (z *Int) Add(x, y *Int) *Int
该方法会将 z 转换为 x + y 并返回 z。package main import ( "fmt" "math/big" "time" ) const LIM = 1000 //求第1000位的斐波那契数列 var fibs [LIM]*big.Int //使用数组保存计算出来的数列的指针 func main() { result := big.NewInt(0) start := time.Now() for i := 0; i < LIM; i++ { result = fibonacci(i) fmt.Printf("数列第 %d 位: %d\n", i+1, result) } end := time.Now() delta := end.Sub(start) fmt.Printf("执行完成,所耗时间为: %s\n", delta) } func fibonacci(n int) (res *big.Int) { if n <= 1 { res = big.NewInt(1) } else { temp := new(big.Int) res = temp.Add(fibs[n-1], fibs[n-2]) } fibs[n] = res return }运行结果如下:
数列第 1 位: 1
数列第 2 位: 1
数列第 3 位: 2
数列第 4 位: 3
数列第 5 位: 5
...
数列第 997 位: 10261062362033262336604926729245222132668558120602124277764622905699407982546711488272859468887457959
08773311924256407785074365766118082732679853917775891982813511440749936979646564952426675539110499009
9120377
数列第 998 位: 16602747662452097049541800472897701834948051198384828062358553091918573717701170201065510185595898605
10409473691887927846223301598102952299783631123261876053919903676539979992673143323971886037334508837
5054249
数列第 999 位: 26863810024485359386146727202142923967616609318986952340123175997617981700247881689338369654483356564
19182785616144335631297667364221035032463485041037768036733415117289916972319708276398561576445007847
4174626
数列第 1000 位: 4346655768693745643568852767504062580256466051737178040248172908953655541794905189040387984007925516
92959225930803226347752096896232398733224711616429964409065331879382989696499285160037044761377951668
49228875
执行完成,所耗时间为: 6.945ms
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