plain old C, to be called via ctypes

[jsbueno]

we can format this a sa pr later, but it is this thing:

unsigned long long count_double(char *str) {
    char *i, c1, c2;
    unsigned long long  count = 0;

    c1 = *str;
    c2 = *(str + 1);
    for(i = str+1; c2 = *i; i++) {
        count += (c1 == c2);
        c1 = c2;
    }
    return count;
}

Build with:
gcc -shared -o libblacount.so -fPIC blacount.c

And prepare to use from Python with:

import ctypes
blacount = ctypes.cdll.LoadLibrary("./libblacount.so")
blacount.count_double.argtypes = [ctypes.c_char_p]
blacount.count_double.restype = ctypes.c_uint64

(it counts byte-strings only)

[rochacbruno]

@jsbueno I also saw this martinxyz@f8e36ab5f9c

Good comparison but as C is counting bytes we can say Rust is playing good as difference is not so significant

[rochacbruno]

I added a version using SWIG if you think using ctypes will perform better please send a PR :)

-------------------------------------------------------------------------------------------------
Name (time in us)                     Min                    Max                   Mean          
-------------------------------------------------------------------------------------------------
test_rust_bytes_once             476.7920 (1.0)         830.5610 (1.0)         486.6116 (1.0)    
test_c_swig_bytes_once           795.3460 (1.67)      1,504.3380 (1.81)        827.3898 (1.70)   
test_rust_once                   985.9520 (2.07)      1,483.8120 (1.79)      1,017.4251 (2.09)   
test_numpy                     1,001.3880 (2.10)      2,461.1200 (2.96)      1,274.8132 (2.62)   
test_rust                      2,555.0810 (5.36)      3,066.0430 (3.69)      2,609.7403 (5.36)   
test_regex                    24,787.0670 (51.99)    26,513.1520 (31.92)    25,333.8143 (52.06)  
test_pure_python_once         36,447.0790 (76.44)    48,596.5340 (58.51)    38,074.5863 (78.24)  
test_python_comprehension     49,166.0560 (103.12)   50,832.1220 (61.20)    49,699.2122 (102.13) 
test_pure_python              49,586.3750 (104.00)   50,697.3780 (61.04)    50,148.6596 (103.06) 
test_itertools                56,762.8920 (119.05)   69,660.0200 (83.87)    58,402.9442 (120.02) 
-------------------------------------------------------------------------------------------------