Regular Expressions in Cilk

#include <stdio.h>
#include <cilk/cilk.h>
#include <pcre.h>
#include <string.h>

void print_matches(pcre *re, const char *subject) {
    int ovector[30];
    int rc = pcre_exec(re, NULL, subject, strlen(subject), 0, 0, ovector, 30);
    if (rc < 0) {
        switch (rc) {
            case PCRE_ERROR_NOMATCH: printf("No match\n"); break;
            default: printf("Matching error %d\n", rc); break;
        }
        return;
    }
    for (int i = 0; i < rc; i++) {
        char *substring_start = subject + ovector[2*i];
        int substring_length = ovector[2*i+1] - ovector[2*i];
        printf("%.*s\n", substring_length, substring_start);
    }
}

int main() {
    pcre *re;
    const char *error;
    int erroffset;

    // This tests whether a pattern matches a string.
    re = pcre_compile("p([a-z]+)ch", 0, &error, &erroffset, NULL);
    if (re == NULL) {
        printf("PCRE compilation failed at offset %d: %s\n", erroffset, error);
        return 1;
    }
    int result = pcre_exec(re, NULL, "peach", 5, 0, 0, NULL, 0);
    printf("%s\n", result >= 0 ? "true" : "false");

    // Many methods are available on these structs. Here's
    // a match test like we saw earlier.
    result = pcre_exec(re, NULL, "peach", 5, 0, 0, NULL, 0);
    printf("%s\n", result >= 0 ? "true" : "false");

    // This finds the match for the regexp.
    print_matches(re, "peach punch");

    // The Submatch variants include information about
    // both the whole-pattern matches and the submatches
    // within those matches.
    print_matches(re, "peach punch");

    // The All variants of these functions apply to all
    // matches in the input, not just the first. For
    // example to find all matches for a regexp.
    print_matches(re, "peach punch pinch");

    // Providing a non-negative integer as the second
    // argument to these functions will limit the number
    // of matches.
    // Note: In Cilk, we don't have a direct equivalent to limit matches,
    // so we'll just print all matches.
    print_matches(re, "peach punch pinch");

    // The regexp package can also be used to replace
    // subsets of strings with other values.
    char result_str[100];
    pcre_substitute(re, NULL, "a peach", 7, 0, 0, PCRE_SUBSTITUTE_GLOBAL,
                    "<fruit>", 7, result_str, sizeof(result_str));
    printf("%s\n", result_str);

    pcre_free(re);
    return 0;
}

This Cilk program demonstrates the use of regular expressions using the PCRE (Perl Compatible Regular Expressions) library. Here’s a breakdown of the example:

We include necessary headers and define a helper function print_matches to print all matches found by a regular expression.
In the main function, we compile a regular expression pattern “p([a-z]+)ch” using pcre_compile.
We test if the pattern matches a string using pcre_exec.
We demonstrate finding matches in a string.
We show how to find all matches in a string.
We demonstrate replacing substrings that match the pattern with another string using pcre_substitute.

Note that Cilk doesn’t have a built-in regular expression library like Go does. Instead, we’re using the PCRE library, which is a powerful and widely-used regular expression library in C and C-like languages.

To compile and run this program, you would need to link against the PCRE library. Here’s an example compilation command:

$ cilk++ -o regex_example regex_example.cilk -lpcre
$ ./regex_example

This will compile the Cilk program and link it with the PCRE library, then run the resulting executable.

Remember that Cilk is an extension of C/C++ for parallel computing, so most C/C++ libraries and techniques can be used in Cilk programs. The parallel features of Cilk are not utilized in this example as regular expression operations are typically sequential.

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Regular Expressions in Cilk