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math/big: Added small complete example of big.Int usage

Updates #11241

Change-Id: I9639c4f66cf805a57b087c9f648d3918df105d86
Reviewed-on: https://go-review.googlesource.com/11034
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
ALTree 2015-06-17 12:42:02 +02:00 committed by Robert Griesemer
parent e38bcb58d7
commit f0fee976aa

View File

@ -49,3 +49,31 @@ func ExampleInt_Scan() {
} }
// Output: 18446744073709551617 // Output: 18446744073709551617
} }
// Example_fibonacci demonstrates how to use big.Int to compute the smallest
// Fibonacci number with 100 decimal digits, and find out whether it is prime.
func Example_fibonacci() {
// create and initialize big.Ints from int64s
fib1 := big.NewInt(0)
fib2 := 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 fib1 is smaller than 1e100
for fib1.Cmp(&limit) < 0 {
fib1, fib2 = fib2, fib1.Add(fib1, fib2)
}
fmt.Println(fib1) // 100-digits fibonacci number
// Test fib1 for primality. The ProbablyPrimes parameter sets the number
// of Miller-Rabin rounds to be performed. 20 is a good value.
isPrime := fib1.ProbablyPrime(20)
fmt.Println(isPrime) // false
// Output:
// 1344719667586153181419716641724567886890850696275767987106294472017884974410332069524504824747437757
// false
}