golang.org/x/exp@v0.0.0-20240506185415-9bf2ced13842/shootout/pidigits.go (about)

     1  //go:build ignore
     2  // +build ignore
     3  
     4  /*
     5  Redistribution and use in source and binary forms, with or without
     6  modification, are permitted provided that the following conditions are met:
     7  
     8      * Redistributions of source code must retain the above copyright
     9      notice, this list of conditions and the following disclaimer.
    10  
    11      * Redistributions in binary form must reproduce the above copyright
    12      notice, this list of conditions and the following disclaimer in the
    13      documentation and/or other materials provided with the distribution.
    14  
    15      * Neither the name of "The Computer Language Benchmarks Game" nor the
    16      name of "The Computer Language Shootout Benchmarks" nor the names of
    17      its contributors may be used to endorse or promote products derived
    18      from this software without specific prior written permission.
    19  
    20  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    21  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    22  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    23  ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    24  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    25  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    26  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    27  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    28  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    29  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    30  POSSIBILITY OF SUCH DAMAGE.
    31  */
    32  
    33  /* The Computer Language Benchmarks Game
    34   * http://shootout.alioth.debian.org/
    35   *
    36   * contributed by The Go Authors.
    37   * based on pidigits.c (by Paolo Bonzini & Sean Bartlett,
    38   *                      modified by Michael Mellor)
    39   */
    40  
    41  package main
    42  
    43  import (
    44  	"flag"
    45  	"fmt"
    46  	"math/big"
    47  )
    48  
    49  var n = flag.Int("n", 27, "number of digits")
    50  var silent = flag.Bool("s", false, "don't print result")
    51  
    52  var (
    53  	tmp1  = big.NewInt(0)
    54  	tmp2  = big.NewInt(0)
    55  	tmp3  = big.NewInt(0)
    56  	y2    = big.NewInt(0)
    57  	bigk  = big.NewInt(0)
    58  	numer = big.NewInt(1)
    59  	accum = big.NewInt(0)
    60  	denom = big.NewInt(1)
    61  	ten   = big.NewInt(10)
    62  )
    63  
    64  func extract_digit() int64 {
    65  	if numer.Cmp(accum) > 0 {
    66  		return -1
    67  	}
    68  
    69  	// Compute (numer * 3 + accum) / denom
    70  	tmp1.Lsh(numer, 1)
    71  	tmp1.Add(tmp1, numer)
    72  	tmp1.Add(tmp1, accum)
    73  	tmp1.DivMod(tmp1, denom, tmp2)
    74  
    75  	// Now, if (numer * 4 + accum) % denom...
    76  	tmp2.Add(tmp2, numer)
    77  
    78  	// ... is normalized, then the two divisions have the same result.
    79  	if tmp2.Cmp(denom) >= 0 {
    80  		return -1
    81  	}
    82  
    83  	return tmp1.Int64()
    84  }
    85  
    86  func next_term(k int64) {
    87  	y2.SetInt64(k*2 + 1)
    88  	bigk.SetInt64(k)
    89  
    90  	tmp1.Lsh(numer, 1)
    91  	accum.Add(accum, tmp1)
    92  	accum.Mul(accum, y2)
    93  	numer.Mul(numer, bigk)
    94  	denom.Mul(denom, y2)
    95  }
    96  
    97  func eliminate_digit(d int64) {
    98  	tmp3.SetInt64(d)
    99  	accum.Sub(accum, tmp3.Mul(denom, tmp3))
   100  	accum.Mul(accum, ten)
   101  	numer.Mul(numer, ten)
   102  }
   103  
   104  func printf(s string, arg ...interface{}) {
   105  	if !*silent {
   106  		fmt.Printf(s, arg...)
   107  	}
   108  }
   109  
   110  func main() {
   111  	flag.Parse()
   112  
   113  	var m int // 0 <= m < 10
   114  	for i, k := 0, int64(0); ; {
   115  		d := int64(-1)
   116  		for d < 0 {
   117  			k++
   118  			next_term(k)
   119  			d = extract_digit()
   120  		}
   121  
   122  		printf("%c", d+'0')
   123  
   124  		i++
   125  		m = i % 10
   126  		if m == 0 {
   127  			printf("\t:%d\n", i)
   128  		}
   129  		if i >= *n {
   130  			break
   131  		}
   132  		eliminate_digit(d)
   133  	}
   134  
   135  	if m > 0 {
   136  		printf("%s\t:%d\n", "          "[m:10], *n)
   137  	}
   138  }