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String representation: Don't store memo_ts at all for special strings.
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Cliff Frey discussion result.  Don't know if it's faster, but it passes
tests.
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@kohler
kohler committed Nov 14, 2009
1 parent 6318498 commit d16ca89
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Showing 2 changed files with 77 additions and 85 deletions.
26 changes: 12 additions & 14 deletions include/click/string.hh
View file
Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,7 @@ class String { public:

/** @brief Construct an empty String (with length 0). */
inline String() {
assign_memo(null_memo.real_data, 0, &null_memo);
assign_memo(&null_data, 0, 0);
}

/** @brief Construct a copy of the String @a x. */
Expand Down Expand Up @@ -86,7 +86,7 @@ class String { public:
/** @brief Construct a String equal to "true" or "false" depending on the
* value of @a x. */
explicit inline String(bool x) {
assign_memo(bool_data + (x ? 0 : 5), x ? 4 : 5, &permanent_memo);
assign_memo(bool_data + (x ? 0 : 5), x ? 4 : 5, 0);
}

/** @brief Construct a String containing the single character @a c. */
Expand Down Expand Up @@ -289,8 +289,7 @@ class String { public:
// stable). We are guaranteed, in these strings, that _data[_length]
// exists. Otherwise must check that _data[_length] exists.
const char *end_data = _r.data + _r.length;
if ((_r.memo->capacity
&& end_data >= _r.memo->real_data + _r.memo->dirty)
if ((_r.memo && end_data >= _r.memo->real_data + _r.memo->dirty)
|| *end_data != '\0') {
if (char *x = const_cast<String *>(this)->append_garbage(1)) {
*x = '\0';
Expand Down Expand Up @@ -585,15 +584,15 @@ class String { public:

/** @brief Return true iff the String's data is shared or immutable. */
inline bool data_shared() const {
return !_r.memo->capacity || _r.memo->refcount != 1;
return !_r.memo || _r.memo->refcount != 1;
}

/** @brief Return a compact version of this String.
*
* The compact version shares no more than 256 bytes of data with any
* other non-stable String. */
inline String compact() const {
if (!_r.memo->capacity || _r.memo->refcount == 1
if (!_r.memo || _r.memo->refcount == 1
|| (uint32_t) _r.length + 256 >= _r.memo->capacity)
return *this;
else
Expand All @@ -612,7 +611,7 @@ class String { public:

/** @brief Return true iff this is an out-of-memory string. */
inline bool out_of_memory() const {
return _r.data == oom_memo.real_data;
return _r.data == &oom_data;
}

/** @brief Return a const reference to an out-of-memory String. */
Expand All @@ -625,7 +624,7 @@ class String { public:
* The returned value may be dereferenced; it points to a null
* character. */
static inline const char *out_of_memory_data() {
return oom_memo.real_data;
return &oom_data;
}


Expand Down Expand Up @@ -706,8 +705,8 @@ class String { public:
inline void assign_memo(const char *data, int length, memo_t *memo) const {
_r.data = data;
_r.length = length;
_r.memo = memo;
atomic_uint32_t::inc(memo->refcount);
if ((_r.memo = memo))
atomic_uint32_t::inc(memo->refcount);
}

inline String(const char *data, int length, memo_t *memo) {
Expand All @@ -719,7 +718,7 @@ class String { public:
}

inline void deref() const {
if (atomic_uint32_t::dec_and_test(_r.memo->refcount))
if (_r.memo && atomic_uint32_t::dec_and_test(_r.memo->refcount))
delete_memo(_r.memo);
}

Expand All @@ -728,11 +727,10 @@ class String { public:
static memo_t *create_memo(char *space, int dirty, int capacity);
static void delete_memo(memo_t *memo);

static const char null_data;
static const char oom_data;
static const char bool_data[11];
static const char int_data[20];
static memo_t null_memo;
static memo_t permanent_memo;
static memo_t oom_memo;
static const rep_t null_string_rep;
static const rep_t oom_string_rep;

Expand Down
136 changes: 65 additions & 71 deletions lib/string.cc
View file
Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,8 @@ CLICK_DECLS
* returns an out-of-memory string.
*/

const char String::null_data = '\0';
const char String::oom_data = '\0';
const char String::bool_data[] = "true\0false";
const char String::int_data[] = "0\0001\0002\0003\0004\0005\0006\0007\0008\0009";

Expand All @@ -74,21 +76,11 @@ const char String::int_data[] = "0\0001\0002\0003\0004\0005\0006\0007\0008\0009"
# define MEMO_INITIALIZER_TAIL
#endif

String::memo_t String::null_memo = {
2, 0, 0 MEMO_INITIALIZER_TAIL, { '\0' }
};
String::memo_t String::permanent_memo = {
1, 0, 0 MEMO_INITIALIZER_TAIL, { '\0' }
};
String::memo_t String::oom_memo = {
2, 0, 0 MEMO_INITIALIZER_TAIL, { '\0' }
};

const String::rep_t String::null_string_rep = {
null_memo.real_data, 0, &null_memo
&null_data, 0, 0
};
const String::rep_t String::oom_string_rep = {
oom_memo.real_data, 0, &oom_memo
&oom_data, 0, 0
};

#if HAVE_STRING_PROFILING
Expand Down Expand Up @@ -206,7 +198,7 @@ String::profile_report(StringAccum &sa, int examples)
String::String(int x)
{
if (x >= 0 && x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
char buf[128];
sprintf(buf, "%d", x);
Expand All @@ -217,7 +209,7 @@ String::String(int x)
String::String(unsigned x)
{
if (x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
char buf[128];
sprintf(buf, "%u", x);
Expand All @@ -228,7 +220,7 @@ String::String(unsigned x)
String::String(long x)
{
if (x >= 0 && x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
char buf[128];
sprintf(buf, "%ld", x);
Expand All @@ -239,7 +231,7 @@ String::String(long x)
String::String(unsigned long x)
{
if (x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
char buf[128];
sprintf(buf, "%lu", x);
Expand All @@ -254,7 +246,7 @@ String::String(unsigned long x)
String::String(long long x)
{
if (x >= 0 && x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
StringAccum sa;
sa << x;
Expand All @@ -265,7 +257,7 @@ String::String(long long x)
String::String(unsigned long long x)
{
if (x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
StringAccum sa;
sa << x;
Expand All @@ -278,7 +270,7 @@ String::String(unsigned long long x)
String::String(int64_t x)
{
if (x >= 0 && x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
StringAccum sa;
sa << x;
Expand All @@ -289,7 +281,7 @@ String::String(int64_t x)
String::String(uint64_t x)
{
if (x < 10)
assign_memo(int_data + 2 * x, 1, &permanent_memo);
assign_memo(int_data + 2 * x, 1, 0);
else {
StringAccum sa;
sa << x;
Expand Down Expand Up @@ -320,7 +312,7 @@ String::make_stable(const char *s, int len)
{
if (len < 0)
len = (s ? strlen(s) : 0);
return String(s, len, &permanent_memo);
return String(s, len, 0);
}

String
Expand Down Expand Up @@ -350,66 +342,67 @@ String::make_numeric(uint_large_t num, int base, bool uppercase)
void
String::assign_out_of_memory()
{
if (_r.memo)
deref();
_r.memo = &oom_memo;
_r.data = _r.memo->real_data;
_r.length = 0;
atomic_uint32_t::inc(oom_memo.refcount);
if (_r.memo)
deref();
_r.memo = 0;
_r.data = &oom_data;
_r.length = 0;
}

void
String::assign(const char *str, int len, bool need_deref)
{
if (!str) {
assert(len <= 0);
len = 0;
} else if (len < 0)
len = strlen(str);

// need to start with dereference
if (need_deref) {
if (unlikely(str >= _r.memo->real_data
&& str + len <= _r.memo->real_data + _r.memo->capacity)) {
// Be careful about "String s = ...; s = s.c_str();"
_r.data = str;
_r.length = len;
return;
} else
deref();
}

if (len == 0) {
_r.memo = (str == oom_memo.real_data ? &oom_memo : &null_memo);
atomic_uint32_t::inc(_r.memo->refcount);

} else {
// Make the memo a multiple of 16 characters and bigger than 'len'.
int memo_capacity = (len + 15 + MEMO_SPACE) & ~15;
_r.memo = create_memo(0, len, memo_capacity - MEMO_SPACE);
if (!_r.memo) {
assign_out_of_memory();
return;
if (!str) {
assert(len <= 0);
len = 0;
} else if (len < 0)
len = strlen(str);

// need to start with dereference
if (need_deref) {
if (unlikely(_r.memo
&& str >= _r.memo->real_data
&& str + len <= _r.memo->real_data + _r.memo->capacity)) {
// Be careful about "String s = ...; s = s.c_str();"
_r.data = str;
_r.length = len;
return;
} else
deref();
}

if (len == 0) {
_r.memo = 0;
_r.data = (str == &oom_data ? str : &null_data);

} else {
// Make the memo a multiple of 16 characters and bigger than 'len'.
int memo_capacity = (len + 15 + MEMO_SPACE) & ~15;
_r.memo = create_memo(0, len, memo_capacity - MEMO_SPACE);
if (!_r.memo) {
assign_out_of_memory();
return;
}
memcpy(_r.memo->real_data, str, len);
_r.data = _r.memo->real_data;
}
memcpy(_r.memo->real_data, str, len);
}

_r.data = _r.memo->real_data;
_r.length = len;
_r.length = len;
}

char *
String::append_garbage(int len)
{
// Appending anything to "out of memory" leaves it as "out of memory"
if (len <= 0 || _r.memo == &oom_memo)
if (len <= 0 || _r.data == &oom_data)
return 0;

// If we can, append into unused space. First, we check that there's
// enough unused space for 'len' characters to fit; then, we check
// that the unused space immediately follows the data in '*this'.
uint32_t dirty = _r.memo->dirty;
if (_r.memo->capacity > dirty + len) {
uint32_t dirty;
if (_r.memo
&& ((dirty = _r.memo->dirty), _r.memo->capacity > dirty + len)) {
char *real_dirty = _r.memo->real_data + dirty;
if (real_dirty == _r.data + _r.length
&& atomic_uint32_t::compare_and_swap(_r.memo->dirty, dirty, dirty + len)) {
Expand Down Expand Up @@ -467,13 +460,14 @@ String::append(const char *s, int len)
} else if (len < 0)
len = strlen(s);

if (s == oom_memo.real_data)
if (s == &oom_data)
// Appending "out of memory" to a regular string makes it "out of
// memory"
assign_out_of_memory();
else if (unlikely(len == 0))
/* do nothing */;
else if (likely(!(s >= _r.memo->real_data
else if (likely(!(_r.memo
&& s >= _r.memo->real_data
&& s + len <= _r.memo->real_data + _r.memo->capacity))) {
if (char *space = append_garbage(len))
memcpy(space, s, len);
Expand All @@ -497,12 +491,12 @@ String::mutable_data()
{
// If _memo has a capacity (it's not one of the special strings) and it's
// uniquely referenced, return _data right away.
if (_r.memo->capacity && _r.memo->refcount == 1)
if (_r.memo && _r.memo->refcount == 1)
return const_cast<char *>(_r.data);

// Otherwise, make a copy of it. Rely on: deref() doesn't change _data or
// _length; and if _capacity == 0, then deref() doesn't free _real_data.
assert(!_r.memo->capacity || _r.memo->refcount > 1);
assert(!_r.memo || _r.memo->refcount > 1);
deref();
assign(_r.data, _r.length, false);
return const_cast<char *>(_r.data);
Expand Down Expand Up @@ -794,7 +788,7 @@ String::equals(const char *s, int len) const
else if (_r.data == s)
return true;
else if (len == 0)
return (s != oom_memo.real_data && _r.memo != &oom_memo);
return (s != &oom_data && _r.data != &oom_data);
else
return memcmp(_r.data, s, len) == 0;
}
Expand All @@ -810,7 +804,7 @@ String::starts_with(const char *s, int len) const
else if (_r.data == s)
return true;
else if (len == 0)
return (s != oom_memo.real_data && _r.memo != &oom_memo);
return (s != &oom_data && _r.data != &oom_data);
else
return memcmp(_r.data, s, len) == 0;
}
Expand All @@ -822,9 +816,9 @@ String::compare(const char *s, int len) const
len = strlen(s);
if (_r.data == s)
return _r.length - len;
else if (_r.memo == &oom_memo)
else if (_r.data == &oom_data)
return 1;
else if (s == oom_memo.real_data)
else if (s == &oom_data)
return -1;
else if (_r.length == len)
return memcmp(_r.data, s, len);
Expand Down

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