github.com/huandu/go@v0.0.0-20151114150818-04e615e41150/misc/cgo/gmp/pi.go (about)

     1  // +build ignore
     2  
     3  /*
     4  Redistribution and use in source and binary forms, with or without
     5  modification, are permitted provided that the following conditions are met:
     6  
     7      * Redistributions of source code must retain the above copyright
     8      notice, this list of conditions and the following disclaimer.
     9  
    10      * Redistributions in binary form must reproduce the above copyright
    11      notice, this list of conditions and the following disclaimer in the
    12      documentation and/or other materials provided with the distribution.
    13  
    14      * Neither the name of "The Computer Language Benchmarks Game" nor the
    15      name of "The Computer Language Shootout Benchmarks" nor the names of
    16      its contributors may be used to endorse or promote products derived
    17      from this software without specific prior written permission.
    18  
    19  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    20  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    21  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    22  ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    23  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    24  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    25  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    26  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    27  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    28  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    29  POSSIBILITY OF SUCH DAMAGE.
    30  */
    31  
    32  /* The Computer Language Benchmarks Game
    33   * http://shootout.alioth.debian.org/
    34   *
    35   * contributed by The Go Authors.
    36   * based on pidigits.c (by Paolo Bonzini & Sean Bartlett,
    37   *                      modified by Michael Mellor)
    38   */
    39  
    40  package main
    41  
    42  import (
    43  	big "."
    44  	"fmt"
    45  	"runtime"
    46  )
    47  
    48  var (
    49  	tmp1  = big.NewInt(0)
    50  	tmp2  = big.NewInt(0)
    51  	numer = big.NewInt(1)
    52  	accum = big.NewInt(0)
    53  	denom = big.NewInt(1)
    54  	ten   = big.NewInt(10)
    55  )
    56  
    57  func extractDigit() int64 {
    58  	if big.CmpInt(numer, accum) > 0 {
    59  		return -1
    60  	}
    61  	tmp1.Lsh(numer, 1).Add(tmp1, numer).Add(tmp1, accum)
    62  	big.DivModInt(tmp1, tmp2, tmp1, denom)
    63  	tmp2.Add(tmp2, numer)
    64  	if big.CmpInt(tmp2, denom) >= 0 {
    65  		return -1
    66  	}
    67  	return tmp1.Int64()
    68  }
    69  
    70  func nextTerm(k int64) {
    71  	y2 := k*2 + 1
    72  	accum.Add(accum, tmp1.Lsh(numer, 1))
    73  	accum.Mul(accum, tmp1.SetInt64(y2))
    74  	numer.Mul(numer, tmp1.SetInt64(k))
    75  	denom.Mul(denom, tmp1.SetInt64(y2))
    76  }
    77  
    78  func eliminateDigit(d int64) {
    79  	accum.Sub(accum, tmp1.Mul(denom, tmp1.SetInt64(d)))
    80  	accum.Mul(accum, ten)
    81  	numer.Mul(numer, ten)
    82  }
    83  
    84  func main() {
    85  	i := 0
    86  	k := int64(0)
    87  	for {
    88  		d := int64(-1)
    89  		for d < 0 {
    90  			k++
    91  			nextTerm(k)
    92  			d = extractDigit()
    93  		}
    94  		eliminateDigit(d)
    95  		fmt.Printf("%c", d+'0')
    96  
    97  		if i++; i%50 == 0 {
    98  			fmt.Printf("\n")
    99  			if i >= 1000 {
   100  				break
   101  			}
   102  		}
   103  	}
   104  
   105  	fmt.Printf("\n%d calls; bit sizes: %d %d %d\n", runtime.NumCgoCall(), numer.Len(), accum.Len(), denom.Len())
   106  }