// This example demonstrates how to use big.Int to compute the smallest
// Fibonacci number with 100 decimal digits and to test whether it is prime.
func Example_fibonacci() {
// Initialize two big ints with the first two numbers in the sequence.
a := big.NewInt(0)
b := big.NewInt(1)
// Initialize limit as 10^99, the smallest integer with 100 digits.
var limit big.Int
limit.Exp(big.NewInt(10), big.NewInt(99), nil)
// Loop while a is smaller than 1e100.
for a.Cmp(&limit) < 0 {
// Compute the next Fibonacci number, storing it in a.
a.Add(a, b)
// Swap a and b so that b is the next number in the sequence.
a, b = b, a
}
fmt.Println(a) // 100-digit Fibonacci number
// Test a for primality.
// (ProbablyPrimes' argument sets the number of Miller-Rabin
// rounds to be performed. 20 is a good value.)
fmt.Println(a.ProbablyPrime(20))
// Output:
// 1344719667586153181419716641724567886890850696275767987106294472017884974410332069524504824747437757
// false
}
func bignodes() {
if bignodes_did {
return
}
bignodes_did = true
var i big.Int
i.SetInt64(1)
i.Lsh(&i, 63)
gc.Nodconst(&bigi, gc.Types[gc.TUINT64], 0)
bigi.SetBigInt(&i)
bigi.Convconst(&bigf, gc.Types[gc.TFLOAT64])
}
func (p *importer) float(x *Mpflt) {
sign := p.int()
if sign == 0 {
Mpmovecflt(x, 0)
return
}
exp := p.int()
mant := new(big.Int).SetBytes([]byte(p.string()))
m := x.Val.SetInt(mant)
m.SetMantExp(m, exp-mant.BitLen())
if sign < 0 {
m.Neg(m)
}
}
func bignodes() {
if bignodes_did {
return
}
bignodes_did = true
gc.Nodconst(&zerof, gc.Types[gc.TINT64], 0)
zerof.Convconst(&zerof, gc.Types[gc.TFLOAT64])
var i big.Int
i.SetInt64(1)
i.Lsh(&i, 63)
var bigi gc.Node
gc.Nodconst(&bigi, gc.Types[gc.TUINT64], 0)
bigi.SetBigInt(&i)
bigi.Convconst(&two63f, gc.Types[gc.TFLOAT64])
gc.Nodconst(&bigi, gc.Types[gc.TUINT64], 0)
i.Lsh(&i, 1)
bigi.SetBigInt(&i)
bigi.Convconst(&two64f, gc.Types[gc.TFLOAT64])
}
func ExampleInt_SetString() {
i := new(big.Int)
i.SetString("644", 8) // octal
fmt.Println(i)
// Output: 420
}