libakstdlib/tests/test_strhash.c

/*
 * aksl_strhash_djb2 -- TODO.md section 1.6.
 *
 * The expected values are the canonical djb2 ones: h = 5381, then
 * h = h * 33 + byte for each of len bytes, truncated to 32 bits. They were
 * computed independently of this implementation.
 *
 * Every vector here is 7-bit ASCII, where signed and unsigned char agree. The
 * high-bit case ("\xff\xfe") is the sign-extension defect in TODO.md 2.2.6 and
 * is left for a test that can be registered as a known failure.
 */

#include "aksl_capture.h"

static int test_empty_string_is_the_djb2_seed(void)
{
    uint32_t h = 0;

    AKSL_CHECK_OK(aksl_strhash_djb2("", 0, &h));
    AKSL_CHECK(h == 5381);
    return 0;
}

/* len drives the loop, so a zero length ignores the contents entirely. */
static int test_zero_length_ignores_the_buffer(void)
{
    char buf[] = "ignored";
    uint32_t h = 0;

    AKSL_CHECK_OK(aksl_strhash_djb2(buf, 0, &h));
    AKSL_CHECK(h == 5381);
    return 0;
}

static int test_known_answer_vectors(void)
{
    char hello[] = "hello";
    char libname[] = "libakstdlib";
    uint32_t h = 0;

    AKSL_CHECK_OK(aksl_strhash_djb2(hello, 5, &h));
    AKSL_CHECK(h == 261238937u);

    AKSL_CHECK_OK(aksl_strhash_djb2(libname, 11, &h));
    AKSL_CHECK(h == 884285482u);
    return 0;
}

/* The function is length-driven, not NUL-driven: an embedded NUL is hashed. */
static int test_embedded_nul_is_hashed(void)
{
    char buf[3] = { 'a', '\0', 'b' };
    uint32_t whole = 0;
    uint32_t prefix = 0;

    AKSL_CHECK_OK(aksl_strhash_djb2(buf, sizeof(buf), &whole));
    AKSL_CHECK(whole == 193482728u);

    /* Stopping at the NUL would give the one-byte hash instead. */
    AKSL_CHECK_OK(aksl_strhash_djb2(buf, 1, &prefix));
    AKSL_CHECK(prefix != whole);
    return 0;
}

static int test_hash_is_stable_across_calls(void)
{
    char buf[] = "repeatable";
    uint32_t first = 0;
    uint32_t second = 0;

    AKSL_CHECK_OK(aksl_strhash_djb2(buf, sizeof(buf) - 1, &first));
    AKSL_CHECK_OK(aksl_strhash_djb2(buf, sizeof(buf) - 1, &second));
    AKSL_CHECK(first == second);
    return 0;
}

static int test_rejects_null_arguments(void)
{
    char buf[] = "x";
    uint32_t h = 0;

    AKSL_CHECK_STATUS_MSG_CONTAINS(aksl_strhash_djb2(NULL, 1, &h),
                                   AKERR_NULLPOINTER, "str");
    AKSL_CHECK_STATUS_MSG_CONTAINS(aksl_strhash_djb2(buf, 1, NULL),
                                   AKERR_NULLPOINTER, "hashval");
    return 0;
}

int main(void)
{
    int failures = 0;

    akerr_init();

    AKSL_RUN(failures, test_empty_string_is_the_djb2_seed);
    AKSL_RUN(failures, test_zero_length_ignores_the_buffer);
    AKSL_RUN(failures, test_known_answer_vectors);
    AKSL_RUN(failures, test_embedded_nul_is_hashed);
    AKSL_RUN(failures, test_hash_is_stable_across_calls);
    AKSL_RUN(failures, test_rejects_null_arguments);

    AKSL_REPORT(failures);
}