misc/cgo/gmp/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 }