github.com/razvanm/vanadium-go-1.3@v0.0.0-20160721203343-4a65068e5915/test/bench/shootout/pidigits.go (about)

     1  /*
     2  Redistribution and use in source and binary forms, with or without
     3  modification, are permitted provided that the following conditions are met:
     4  
     5      * Redistributions of source code must retain the above copyright
     6      notice, this list of conditions and the following disclaimer.
     7  
     8      * Redistributions in binary form must reproduce the above copyright
     9      notice, this list of conditions and the following disclaimer in the
    10      documentation and/or other materials provided with the distribution.
    11  
    12      * Neither the name of "The Computer Language Benchmarks Game" nor the
    13      name of "The Computer Language Shootout Benchmarks" nor the names of
    14      its contributors may be used to endorse or promote products derived
    15      from this software without specific prior written permission.
    16  
    17  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    18  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    19  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    20  ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    21  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    22  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    23  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    24  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    25  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    26  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    27  POSSIBILITY OF SUCH DAMAGE.
    28  */
    29  
    30  /* The Computer Language Benchmarks Game
    31   * http://shootout.alioth.debian.org/
    32   *
    33   * contributed by The Go Authors.
    34   * based on pidigits.c (by Paolo Bonzini & Sean Bartlett,
    35   *                      modified by Michael Mellor)
    36   */
    37  
    38  package main
    39  
    40  import (
    41  	"flag"
    42  	"fmt"
    43  	"math/big"
    44  )
    45  
    46  var n = flag.Int("n", 27, "number of digits")
    47  var silent = flag.Bool("s", false, "don't print result")
    48  
    49  var (
    50  	tmp1  = big.NewInt(0)
    51  	tmp2  = big.NewInt(0)
    52  	tmp3  = big.NewInt(0)
    53  	y2    = big.NewInt(0)
    54  	bigk  = big.NewInt(0)
    55  	numer = big.NewInt(1)
    56  	accum = big.NewInt(0)
    57  	denom = big.NewInt(1)
    58  	ten   = big.NewInt(10)
    59  )
    60  
    61  func extract_digit() int64 {
    62  	if numer.Cmp(accum) > 0 {
    63  		return -1
    64  	}
    65  
    66  	// Compute (numer * 3 + accum) / denom
    67  	tmp1.Lsh(numer, 1)
    68  	tmp1.Add(tmp1, numer)
    69  	tmp1.Add(tmp1, accum)
    70  	tmp1.DivMod(tmp1, denom, tmp2)
    71  
    72  	// Now, if (numer * 4 + accum) % denom...
    73  	tmp2.Add(tmp2, numer)
    74  
    75  	// ... is normalized, then the two divisions have the same result.
    76  	if tmp2.Cmp(denom) >= 0 {
    77  		return -1
    78  	}
    79  
    80  	return tmp1.Int64()
    81  }
    82  
    83  func next_term(k int64) {
    84  	y2.SetInt64(k*2 + 1)
    85  	bigk.SetInt64(k)
    86  
    87  	tmp1.Lsh(numer, 1)
    88  	accum.Add(accum, tmp1)
    89  	accum.Mul(accum, y2)
    90  	numer.Mul(numer, bigk)
    91  	denom.Mul(denom, y2)
    92  }
    93  
    94  func eliminate_digit(d int64) {
    95  	tmp3.SetInt64(d)
    96  	accum.Sub(accum, tmp3.Mul(denom, tmp3))
    97  	accum.Mul(accum, ten)
    98  	numer.Mul(numer, ten)
    99  }
   100  
   101  func printf(s string, arg ...interface{}) {
   102  	if !*silent {
   103  		fmt.Printf(s, arg...)
   104  	}
   105  }
   106  
   107  func main() {
   108  	flag.Parse()
   109  
   110  	var m int // 0 <= m < 10
   111  	for i, k := 0, int64(0); ; {
   112  		d := int64(-1)
   113  		for d < 0 {
   114  			k++
   115  			next_term(k)
   116  			d = extract_digit()
   117  		}
   118  
   119  		printf("%c", d+'0')
   120  
   121  		i++
   122  		m = i % 10
   123  		if m == 0 {
   124  			printf("\t:%d\n", i)
   125  		}
   126  		if i >= *n {
   127  			break
   128  		}
   129  		eliminate_digit(d)
   130  	}
   131  
   132  	if m > 0 {
   133  		printf("%s\t:%d\n", "          "[m:10], *n)
   134  	}
   135  }