The Use of c++decl

cdecl and c++decl are two nice tools to check syntax or to generate declaration of C and C++ respectively.

for example, using c++decl (the text in bold is the one we type):

$ cdecl

Type `help' or `?' for help
c++decl>

c++decl> declare foo as pointer to member of class X function (arg1, arg2) returning reference to class Y

class Y &(X::*foo)(arg1, arg2)

c++decl>

c++decl> declare foo as reference to class X

class X &foo

c++decl>

c++decl> cast foo into reference to class X

(class X &)foo

c++decl>

We can also use them to check a declaration syntax, for example:

c++decl> explain int (*a)[5]

declare a as pointer to array 5 of int

c++decl>

c++decl> explain long **foo[10]

declare foo as array 10 of pointer to pointer to long

c++decl>

c++decl> explain int*&(foo);

declare foo as reference to pointer to int

c++decl>

The function can also be used to translate an english declaration to C (or C++) declaration.  For example:

$ c++decl declare "i as array 5 of pointer to function(int,int) returning reference to class X"

class X &(*i[5])(int , int )

$

$ c++decl declare "i as array 5 of pointer to function(reference to class X,constant reference to int) returning reference to class X"

class X &(*i[5])(class X &, int & const )

$

$ c++decl declare "const_ptr as const pointer to const int"

const int * const const_ptr

$ c++decl declare "const_ptr as const pointer to const reference to class X"

class X & const * const const_ptr

$

c++decl> declare myfunc as const pointer to function (const pointer to int, reference to class X) returning void

void (* const myfunc)(int * const , class X &)

c++decl>

c++decl> declare myfunctpr as array of pointer to function (void) returning int

int (*myfunctpr[])(void )

c++decl>

declare myptr as pointer to array 10 of struct MyStruct

struct MyStruct (*myptr)[10]

c++decl>

Odd Numbers with Parity

#!/usr/bin/python

table=[]
for n in range(0,256):
    p=False
    while n:
        p = not p
        n &= n-1
    table.append(p)

parity_odd = []

print "Odd numbers with Parity:"



for i in range(0,256):
    if (i%2) and (table[i]):
        parity_odd.append(i)
        print i,

Result:

Odd numbers with Parity:
1 7 11 13 19 21 25 31 35 37 41 47 49 55 59 61 67 69 73 79 81 87 91 93 97 103 107 109 115 117 121 127 131 133 137 143 145 151 155 157 161 167 171 173 179 181 185 191 193 199 203 205 211 213 217 223 227 229 233 239 241 247 251 253

Fastest Fibonacci Sequencer

This algorithm is based on Fast-doubling  as explained in Fast Fibonacci algorithms.

Given F(k) and F(k+1), we can calculate these equations:

F(2k) = F(k)[2F(k+1)−F(k)]
F(2k+1) = F(k+1)2+F(k)2.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117

#include <stdio.h> #include <stdlib.h> #include <sys/types.h> #ifdef DEBUG #define DBGMSG(x) printf x #else #define DBGMSG(x) #endif typedef unsigned long long num_type; void _fib(int n, num_type *fn, num_type *fn_1); num_type fibonacci(uint n, num_type *s) { int i; num_type fn=0, fn_1=1; if (!s) return 0; if (n < 2) { return 1; } for(i=1; i<n; i++) { _fib(i, &fn, &fn_1); DBGMSG(("i=%u, n=%u, fn=%llu, fn+1=%llu\n", i, n, fn, fn_1)); s[i] = fn; } return s[n]; } /* * This is base on matrix exponentiation algorithm: * where: * f(2k) = f(k)*{ 2*f(k+1) - f(k)} ---> c * f(2k+1) = f(k)^2 + f(k+1)^2 ---> s * * if we plugin k = n/2, we get f(n) and f(n+1) */ void _fib(int n, num_type *fn, num_type *fn_1) { num_type c,d; num_type a, b; DBGMSG( ("%s: Initially n=%u, fn=%llu, fn_1=%llu\n", __FUNCTION__, n, *fn, *fn_1) ); if (n==0) { *fn = 0; // fn *fn_1 = 1; // fn+1 return; } else { a = *fn; b = *fn_1; } _fib(n>>1, &a, &b); DBGMSG (("%s: local fn=%llu, fn_1=%llu\n", __FUNCTION__, a, b)); c = a * (2*b - a); d = b*b + a*a; DBGMSG( ("%s: c=%llu, d=%llu\n", __FUNCTION__, c, d) ); if (n % 2 == 0) { // n is even *fn = c; *fn_1 = d; } else { *fn = d; *fn_1 = c+d; } } int main(int argc, char *argv[]) { uint n; uint f; int i; num_type *result; char *sbuf; int status = 0; if (argc > 1) n = atoi(argv[1]); else { printf("Enter a number: "); sbuf = (char *)malloc(50); status = (getline(&sbuf, &n, stdin) > 0); if (status == 0) { n = atoi(sbuf); free(sbuf); } else { printf("Error in input\n"); return (1); } } if (n <= 0) { printf("What have yo done???\n"); return(0); } if (status == 0) { result = (num_type *)malloc(n*sizeof(unsigned long long)); f = fibonacci(n, result); printf("Fibonacci sequence: "); for(i=0; i<n; i++) printf("%llu ", result[i]); printf("\n"); if (result) free(result); } }