static u32 util_popcount(u64 x) {
#ifdef __GNUC__
	return (u32)__builtin_popcountll(x);
#else
	u32 count = 0;
	while (x) {
		x &= x-1;
		++count;
	}
	return count;
#endif
}

static bool util_is_power_of_2(u64 x) {
	return util_popcount(x) == 1;
}

static void util_zero_memory(void *mem, size_t size) {
	memset(mem, 0, size);
}

// for finding a character in a char32 string
static char32_t *util_mem32chr(char32_t *s, char32_t c, size_t n) {
	for (size_t i = 0; i < n; ++i) {
		if (s[i] == c) {
			return &s[i];
		}
	}
	return NULL;
}

static char32_t const *util_mem32chr_const(char32_t const *s, char32_t c, size_t n) {
	for (size_t i = 0; i < n; ++i) {
		if (s[i] == c) {
			return &s[i];
		}
	}
	return NULL;
}

static bool str_is_prefix(char const *str, char const *prefix) {
	return strncmp(str, prefix, strlen(prefix)) == 0;
}

static bool streq(char const *a, char const *b) {
	return strcmp(a, b) == 0;
}

// duplicates a null-terminated string. the returned string should be passed to free()
static char *str_dup(char const *src) {
	size_t len = strlen(src);
	char *ret = malloc(len + 1);
	if (ret)
		memcpy(ret, src, len + 1);
	return ret;
}

// like snprintf, but not screwed up on windows
#define str_printf(str, size, ...) (str)[(size) - 1] = '\0', snprintf((str), (size) - 1, __VA_ARGS__)
// like snprintf, but the size is taken to be the length of the array str.
//                              first, check that str is actually an array
#define strbuf_printf(str, ...) assert(sizeof str != 4 && sizeof str != 8), \
	str_printf(str, sizeof str, __VA_ARGS__)

// on 16-bit systems, this is 16383. on 32/64-bit systems, this is 1073741823
// it is unusual to have a string that long.
#define STRLEN_SAFE_MAX (UINT_MAX >> 2)

// safer version of strcat. dst_sz includes a null terminator.
static void str_cat(char *dst, size_t dst_sz, char const *src) {
	size_t dst_len = strlen(dst), src_len = strlen(src);

	// make sure dst_len + src_len + 1 doesn't overflow
	if (dst_len > STRLEN_SAFE_MAX || src_len > STRLEN_SAFE_MAX) {
		assert(0);
		return;
	}

	if (dst_len >= dst_sz) {
		// dst doesn't actually contain a null-terminated string!
		assert(0);
		return;
	}

	if (dst_len + src_len + 1 > dst_sz) {
		// number of bytes left in dst, not including null terminator
		size_t n = dst_sz - dst_len - 1;
		memcpy(dst + dst_len, src, n);
		dst[dst_sz - 1] = 0; // dst_len + n == dst_sz - 1
	} else {
		memcpy(dst + dst_len, src, src_len);
		dst[dst_len + src_len] = 0;
	}
}

// safer version of strncpy. dst_sz includes a null terminator.
static void str_cpy(char *dst, size_t dst_sz, char const *src) {
	size_t srclen = strlen(src);
	size_t n = srclen; // number of bytes to copy
	
	if (dst_sz == 0) {
		assert(0);
		return;
	}

	if (dst_sz-1 < n)
		n = dst_sz-1;
	memcpy(dst, src, n);
	dst[n] = 0;
}

/* 
returns the first instance of needle in haystack, ignoring the case of the characters,
or NULL if the haystack does not contain needle
WARNING: O(strlen(haystack) * strlen(needle))
*/
static char *stristr(char const *haystack, char const *needle) {
	size_t needle_len = strlen(needle), haystack_len = strlen(haystack), i, j;
	
	if (needle_len > haystack_len) return NULL; // a larger string can't fit in a smaller string

	for (i = 0; i <= haystack_len - needle_len; ++i) {
		char const *p = haystack + i, *q = needle;
		bool match = true;
		for (j = 0; j < needle_len; ++j) {
			if (tolower(*p) != tolower(*q)) {
				match = false;
				break;
			}
			++p;
			++q;
		}
		if (match)
			return (char *)haystack + i;
	}
	return NULL;
}

static void print_bytes(u8 *bytes, size_t n) {
	u8 *b, *end;
	for (b = bytes, end = bytes + n; b != end; ++b)
		printf("%x ", *b);
	printf("\n");
}

/*
does this predicate hold for all the characters of s. predicate is int (*)(int) instead
of bool (*)(char) so that you can pass isprint, etc. to it.
*/
static bool str_satisfies(char const *s, int (*predicate)(int)) {
	char const *p;
	for (p = s; *p; ++p)
		if (!predicate(*p))
			return false;
	return true;
}

// function to be passed into qsort for case insensitive sorting
static int str_qsort_case_insensitive_cmp(const void *av, const void *bv) {
	char const *const *a = av, *const *b = bv;
#if _WIN32
	return _stricmp(*a, *b);
#else
	return strcasecmp(*a, *b);
#endif
}