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