go pi 源码
golang pi 代码
文件路径：/misc/cgo/gmp/pi.go
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build ignore
// +build ignore
package main
import (
big "."
"fmt"
"runtime"
)
var (
tmp1 = big.NewInt(0)
tmp2 = big.NewInt(0)
numer = big.NewInt(1)
accum = big.NewInt(0)
denom = big.NewInt(1)
ten = big.NewInt(10)
)
func extractDigit() int64 {
if big.CmpInt(numer, accum) > 0 {
return -1
}
tmp1.Lsh(numer, 1).Add(tmp1, numer).Add(tmp1, accum)
big.DivModInt(tmp1, tmp2, tmp1, denom)
tmp2.Add(tmp2, numer)
if big.CmpInt(tmp2, denom) >= 0 {
return -1
}
return tmp1.Int64()
}
func nextTerm(k int64) {
y2 := k*2 + 1
accum.Add(accum, tmp1.Lsh(numer, 1))
accum.Mul(accum, tmp1.SetInt64(y2))
numer.Mul(numer, tmp1.SetInt64(k))
denom.Mul(denom, tmp1.SetInt64(y2))
}
func eliminateDigit(d int64) {
accum.Sub(accum, tmp1.Mul(denom, tmp1.SetInt64(d)))
accum.Mul(accum, ten)
numer.Mul(numer, ten)
}
func main() {
i := 0
k := int64(0)
for {
d := int64(-1)
for d < 0 {
k++
nextTerm(k)
d = extractDigit()
}
eliminateDigit(d)
fmt.Printf("%c", d+'0')
if i++; i%50 == 0 {
fmt.Printf("\n")
if i >= 1000 {
break
}
}
}
fmt.Printf("\n%d calls; bit sizes: %d %d %d\n", runtime.NumCgoCall(), numer.Len(), accum.Len(), denom.Len())
}
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