github.com/karrick/go@v0.0.0-20170817181416-d5b0ec858b37/test/bench/garbage/peano.go (about)

     1  // run
     2  
     3  // Copyright 2009 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  import (
    10  	"fmt"
    11  	"runtime"
    12  	"time"
    13  )
    14  
    15  type Number struct {
    16  	next *Number
    17  }
    18  
    19  // -------------------------------------
    20  // Peano primitives
    21  
    22  func zero() *Number { return nil }
    23  
    24  func is_zero(x *Number) bool { return x == nil }
    25  
    26  func add1(x *Number) *Number {
    27  	e := new(Number)
    28  	e.next = x
    29  	return e
    30  }
    31  
    32  func sub1(x *Number) *Number { return x.next }
    33  
    34  func add(x, y *Number) *Number {
    35  	if is_zero(y) {
    36  		return x
    37  	}
    38  
    39  	return add(add1(x), sub1(y))
    40  }
    41  
    42  func mul(x, y *Number) *Number {
    43  	if is_zero(x) || is_zero(y) {
    44  		return zero()
    45  	}
    46  
    47  	return add(mul(x, sub1(y)), x)
    48  }
    49  
    50  func fact(n *Number) *Number {
    51  	if is_zero(n) {
    52  		return add1(zero())
    53  	}
    54  
    55  	return mul(fact(sub1(n)), n)
    56  }
    57  
    58  // -------------------------------------
    59  // Helpers to generate/count Peano integers
    60  
    61  func gen(n int) *Number {
    62  	if n > 0 {
    63  		return add1(gen(n - 1))
    64  	}
    65  
    66  	return zero()
    67  }
    68  
    69  func count(x *Number) int {
    70  	if is_zero(x) {
    71  		return 0
    72  	}
    73  
    74  	return count(sub1(x)) + 1
    75  }
    76  
    77  func check(x *Number, expected int) {
    78  	var c = count(x)
    79  	if c != expected {
    80  		panic(fmt.Sprintf("error: found %d; expected %d", c, expected))
    81  	}
    82  }
    83  
    84  // -------------------------------------
    85  // Test basic functionality
    86  
    87  func verify() {
    88  	check(zero(), 0)
    89  	check(add1(zero()), 1)
    90  	check(gen(10), 10)
    91  
    92  	check(add(gen(3), zero()), 3)
    93  	check(add(zero(), gen(4)), 4)
    94  	check(add(gen(3), gen(4)), 7)
    95  
    96  	check(mul(zero(), zero()), 0)
    97  	check(mul(gen(3), zero()), 0)
    98  	check(mul(zero(), gen(4)), 0)
    99  	check(mul(gen(3), add1(zero())), 3)
   100  	check(mul(add1(zero()), gen(4)), 4)
   101  	check(mul(gen(3), gen(4)), 12)
   102  
   103  	check(fact(zero()), 1)
   104  	check(fact(add1(zero())), 1)
   105  	check(fact(gen(5)), 120)
   106  }
   107  
   108  // -------------------------------------
   109  // Factorial
   110  
   111  func main() {
   112  	t0 := time.Now()
   113  	verify()
   114  	for i := 0; i <= 9; i++ {
   115  		print(i, "! = ", count(fact(gen(i))), "\n")
   116  	}
   117  	runtime.GC()
   118  	t1 := time.Now()
   119  
   120  	gcstats("BenchmarkPeano", 1, t1.Sub(t0))
   121  }