pi.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build ignore
     6  // +build ignore
     7  
     8  package main
     9  
    10  import (
    11  	big "."
    12  	"fmt"
    13  	"runtime"
    14  )
    15  
    16  var (
    17  	tmp1  = big.NewInt(0)
    18  	tmp2  = big.NewInt(0)
    19  	numer = big.NewInt(1)
    20  	accum = big.NewInt(0)
    21  	denom = big.NewInt(1)
    22  	ten   = big.NewInt(10)
    23  )
    24  
    25  func extractDigit() int64 {
    26  	if big.CmpInt(numer, accum) > 0 {
    27  		return -1
    28  	}
    29  	tmp1.Lsh(numer, 1).Add(tmp1, numer).Add(tmp1, accum)
    30  	big.DivModInt(tmp1, tmp2, tmp1, denom)
    31  	tmp2.Add(tmp2, numer)
    32  	if big.CmpInt(tmp2, denom) >= 0 {
    33  		return -1
    34  	}
    35  	return tmp1.Int64()
    36  }
    37  
    38  func nextTerm(k int64) {
    39  	y2 := k*2 + 1
    40  	accum.Add(accum, tmp1.Lsh(numer, 1))
    41  	accum.Mul(accum, tmp1.SetInt64(y2))
    42  	numer.Mul(numer, tmp1.SetInt64(k))
    43  	denom.Mul(denom, tmp1.SetInt64(y2))
    44  }
    45  
    46  func eliminateDigit(d int64) {
    47  	accum.Sub(accum, tmp1.Mul(denom, tmp1.SetInt64(d)))
    48  	accum.Mul(accum, ten)
    49  	numer.Mul(numer, ten)
    50  }
    51  
    52  func main() {
    53  	i := 0
    54  	k := int64(0)
    55  	for {
    56  		d := int64(-1)
    57  		for d < 0 {
    58  			k++
    59  			nextTerm(k)
    60  			d = extractDigit()
    61  		}
    62  		eliminateDigit(d)
    63  		fmt.Printf("%c", d+'0')
    64  
    65  		if i++; i%50 == 0 {
    66  			fmt.Printf("\n")
    67  			if i >= 1000 {
    68  				break
    69  			}
    70  		}
    71  	}
    72  
    73  	fmt.Printf("\n%d calls; bit sizes: %d %d %d\n", runtime.NumCgoCall(), numer.Len(), accum.Len(), denom.Len())
    74  }
    75
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