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.
 *
 * Most vectors here are 7-bit ASCII, where signed and unsigned char agree and
 * the test therefore says nothing either way about byte signedness. The high-bit
 * vector is the one that pins TODO.md 2.2.6 down.
 */

#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;
}

/*
 * TODO.md 2.2.6, pinned. The cursor is an unsigned char * now, so bytes at or
 * above 0x80 contribute their unsigned value. Iterating a plain char * on x86 or
 * ARM Linux made them negative, giving 5859874 here instead of 5868578 -- a hash
 * that disagreed with canonical djb2 and, worse, disagreed with itself across
 * platforms depending on whether char happened to be signed.
 *
 * Benign for the 7-bit identifiers akbasic hashes; quietly wrong for the first
 * caller to key a table on a filename or a UTF-8 string literal.
 */
static int test_high_bit_bytes_are_unsigned(void)
{
    char buf[2] = { (char)0xff, (char)0xfe };
    uint32_t h = 0;

    AKSL_CHECK_OK(aksl_strhash_djb2(buf, sizeof(buf), &h));
    AKSL_CHECK(h == 5868578u);
    /* The sign-extended answer, spelled out so a regression names itself. */
    AKSL_CHECK(h != 5859874u);
    return 0;
}

/* The NUL-terminated convenience form (TODO.md 3.6) agrees with the length one. */
static int test_str_form_matches_the_length_form(void)
{
    const char *s = "libakstdlib";
    uint32_t from_str = 0;
    uint32_t from_len = 0;

    AKSL_CHECK_OK(aksl_strhash_djb2_str(s, &from_str));
    AKSL_CHECK_OK(aksl_strhash_djb2(s, strlen(s), &from_len));
    AKSL_CHECK(from_str == from_len);
    AKSL_CHECK(from_str == 884285482u);

    /* The empty string is the seed, not an error. */
    AKSL_CHECK_OK(aksl_strhash_djb2_str("", &from_str));
    AKSL_CHECK(from_str == 5381);

    AKSL_CHECK_STATUS(aksl_strhash_djb2_str(NULL, &from_str), AKERR_NULLPOINTER);
    AKSL_CHECK_STATUS(aksl_strhash_djb2_str("x", NULL), AKERR_NULLPOINTER);
    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_high_bit_bytes_are_unsigned);
    AKSL_RUN(failures, test_str_form_matches_the_length_form);
    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);
}