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Improve make_greater_string() with encoding-specific incrementers.

Browse source 
This infrastructure doesn't in any way guarantee that the character
we produce will sort before the one we incremented; but it does at least
make it much more likely that we'll end up with something that is a valid
character, which improves our chances.

Kyotaro Horiguchi, with various adjustments by me.
This commit is contained in:
Robert Haas 2011-10-29 14:22:20 -04:00
parent 51eba98cf4
commit 78d523b633
3 changed files with 297 additions and 28 deletions
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65
src/backend/utils/adt/selfuncs.c
View file

@ -5665,6 +5665,19 @@ pattern_selectivity(Const *patt, Pattern_Type ptype)
}
/*
* For bytea, the increment function need only increment the current byte
* (there are no multibyte characters to worry about).
*/
static bool
byte_increment(unsigned char *ptr, int len)
{
if (*ptr >= 255)
return false;
(*ptr)++;
return true;
}
/*
* Try to generate a string greater than the given string or any
* string it is a prefix of. If successful, return a palloc'd string
@ -5704,6 +5717,7 @@ make_greater_string(const Const *str_const, FmgrInfo *ltproc, Oid collation)
int len;
Datum cmpstr;
text *cmptxt = NULL;
mbcharacter_incrementer charinc;
/*
* Get a modifiable copy of the prefix string in C-string format, and set
@ -5765,29 +5779,33 @@ make_greater_string(const Const *str_const, FmgrInfo *ltproc, Oid collation)
}
}
if (datatype == BYTEAOID)
charinc = &byte_increment;
else
charinc = pg_database_encoding_character_incrementer();
while (len > 0)
{
unsigned char *lastchar = (unsigned char *) (workstr + len - 1);
unsigned char savelastchar = *lastchar;
int charlen;
unsigned char *lastchar;
Const *workstr_const;
if (datatype == BYTEAOID)
charlen = 1;
else
charlen = len - pg_mbcliplen(workstr, len, len - 1);
lastchar = (unsigned char *) (workstr + len - charlen);
/*
* Try to generate a larger string by incrementing the last byte.
* Try to generate a larger string by incrementing the last character
* (for BYTEA, we treat each byte as a character).
*/
while (*lastchar < (unsigned char) 255)
if (charinc(lastchar, charlen))
{
Const *workstr_const;
(*lastchar)++;
if (datatype != BYTEAOID)
{
/* do not generate invalid encoding sequences */
if (!pg_verifymbstr(workstr, len, true))
continue;
workstr_const = string_to_const(workstr, datatype);
}
else
if (datatype == BYTEAOID)
workstr_const = string_to_bytea_const(workstr, len);
else
workstr_const = string_to_const(workstr, datatype);
if (DatumGetBool(FunctionCall2Coll(ltproc,
collation,
@ -5806,20 +5824,11 @@ make_greater_string(const Const *str_const, FmgrInfo *ltproc, Oid collation)
pfree(workstr_const);
}
/* restore last byte so we don't confuse pg_mbcliplen */
*lastchar = savelastchar;
/*
* Truncate off the last character, which might be more than 1 byte,
* depending on the character encoding.
* Truncate off the last character or byte.
*/
if (datatype != BYTEAOID && pg_database_encoding_max_length() > 1)
len = pg_mbcliplen(workstr, len, len - 1);
else
len -= 1;
if (datatype != BYTEAOID)
workstr[len] = '\0';
len -= charlen;
workstr[len] = '\0';
}
/* Failed... */

257
src/backend/utils/mb/wchar.c
View file

@ -1334,6 +1334,244 @@ pg_utf8_islegal(const unsigned char *source, int length)
return true;
}
#ifndef FRONTEND
/*
* Generic character increment function.
*
* Not knowing anything about the properties of the encoding in use, we just
* keep incrementing the last byte until pg_verifymbstr() likes the result,
* or we run out of values to try.
*
* Like all character-increment functions, we must restore the original input
* string on failure.
*/
static bool
pg_generic_charinc(unsigned char *charptr, int len)
{
unsigned char *lastchar = (unsigned char *) (charptr + len - 1);
unsigned char savelastchar = *lastchar;
const char *const_charptr = (const char *)charptr;
while (*lastchar < (unsigned char) 255)
{
(*lastchar)++;
if (!pg_verifymbstr(const_charptr, len, true))
continue;
return true;
}
*lastchar = savelastchar;
return false;
}
/*
* UTF-8 character increment function.
*
* For a one-byte character less than 0x7F, we just increment the byte.
*
* For a multibyte character, every byte but the first must fall between 0x80
* and 0xBF; and the first byte must be between 0xC0 and 0xF4. We increment
* the last byte that's not already at its maximum value, and set any following
* bytes back to 0x80. If we can't find a byte that's less than the maximum
* allowable vale, we simply fail. We also have some special-case logic to
* skip regions used for surrogate pair handling, as those should not occur in
* valid UTF-8.
*
* Like all character-increment functions, we must restore the original input
* string on failure.
*/
static bool
pg_utf8_increment(unsigned char *charptr, int length)
{
unsigned char a;
unsigned char bak[4];
unsigned char limit;
switch (length)
{
default:
/* reject lengths 5 and 6 for now */
return false;
case 4:
bak[3] = charptr[3];
a = charptr[3];
if (a < 0xBF)
{
charptr[3]++;
break;
}
charptr[3] = 0x80;
/* FALL THRU */
case 3:
bak[2] = charptr[2];
a = charptr[2];
if (a < 0xBF)
{
charptr[2]++;
break;
}
charptr[2] = 0x80;
/* FALL THRU */
case 2:
bak[1] = charptr[1];
a = charptr[1];
switch (*charptr)
{
case 0xED:
limit = 0x9F;
break;
case 0xF4:
limit = 0x8F;
break;
default:
limit = 0xBF;
break;
}
if (a < limit)
{
charptr[1]++;
break;
}
charptr[1] = 0x80;
/* FALL THRU */
case 1:
bak[0] = *charptr;
a = *charptr;
if (a == 0x7F || a == 0xDF || a == 0xEF || a == 0xF4)
{
/* Restore original string. */
memcpy(charptr, bak, length);
return false;
}
charptr[0]++;
break;
}
return true;
}
/*
* EUC-JP character increment function.
*
* If the sequence starts with SS2(0x8e), it must be a two-byte sequence
* representing JIS X 0201 characters with the second byte ranges between
* 0xa1 and 0xde. We just increment the last byte if it's less than 0xde,
* and otherwise rewrite whole the sequence to 0xa1 0xa1.
*
* If the sequence starts with SS3(0x8f), it must be a three-byte sequence
* which the last two bytes ranges between 0xa1 and 0xfe. The last byte
* is incremented, carrying overflow to the second-to-last byte.
*
* If the sequence starts with the values other than the aboves and its MSB
* is set, it must be a two-byte sequence representing JIS X 0208 characters
* with both bytes ranges between 0xa1 and 0xfe. The last byte is incremented,
* carrying overflow to the second-to-last byte.
*
* Otherwise the sequence is consists of single byte representing ASCII
* characters. It is incremented up to 0x7f.
*
* Only three EUC-JP byte sequences shown below - which have no character
* allocated - make this function to fail in spite of its validity: 0x7f,
* 0xfe 0xfe, 0x8f 0xfe 0xfe.
*/
static bool
pg_eucjp_increment(unsigned char *charptr, int length)
{
unsigned char bak[3];
unsigned char c1, c2;
signed int i;
c1 = *charptr;
switch (c1)
{
case SS2: /* JIS X 0201 */
if (length != 2)
return false;
c2 = charptr[1];
if (c2 > 0xde)
charptr[0] = charptr[1] = 0xa1;
else if (c2 < 0xa1)
charptr[1] = 0xa1;
else
charptr[1]++;
break;
case SS3: /* JIS X 0212 */
if (length != 3)
return false;
for (i = 2; i > 0; i--)
{
bak[i] = charptr[i];
c2 = charptr[i];
if (c2 < 0xa1)
{
charptr[i] = 0xa1;
return true;
}
else if (c2 < 0xfe)
{
charptr[i]++;
break;
}
charptr[i] = 0xa1;
}
if (i == 0) /* Out of 3-byte code region */
{
charptr[1] = bak[1];
charptr[2] = bak[2];
return false;
}
break;
default:
if (IS_HIGHBIT_SET(c1)) /* JIS X 0208? */
{
if (length != 2)
return false;
for (i = 1 ; i >= 0 ; i--) /* i must be signed */
{
bak[i] = charptr[i];
c2 = charptr[i];
if (c2 < 0xa1)
{
charptr[i] = 0xa1;
return true;
}
else if (c2 < 0xfe)
{
charptr[i]++;
break;
}
charptr[i] = 0xa1;
}
if (i < 0) /* Out of 2 byte code region */
{
charptr[0] = bak[0];
charptr[1] = bak[1];
return false;
}
}
else
{ /* ASCII, single byte */
if (c1 > 0x7e)
return false;
(*charptr)++;
}
}
return true;
}
#endif
/*
*-------------------------------------------------------------------
* encoding info table
@ -1458,6 +1696,25 @@ pg_database_encoding_max_length(void)
return pg_wchar_table[GetDatabaseEncoding()].maxmblen;
}
/*
* give the character incrementer for the encoding for the current database
*/
mbcharacter_incrementer
pg_database_encoding_character_incrementer(void)
{
switch (GetDatabaseEncoding())
{
case PG_UTF8:
return pg_utf8_increment;
case PG_EUC_JP:
return pg_eucjp_increment;
default:
return pg_generic_charinc;
}
}
/*
* Verify mbstr to make sure that it is validly encoded in the current
* database encoding. Otherwise same as pg_verify_mbstr().

3
src/include/mb/pg_wchar.h
View file

@ -284,6 +284,8 @@ typedef int (*mblen_converter) (const unsigned char *mbstr);
typedef int (*mbdisplaylen_converter) (const unsigned char *mbstr);
typedef bool (*mbcharacter_incrementer) (unsigned char *mbstr, int len);
typedef int (*mbverifier) (const unsigned char *mbstr, int len);
typedef struct
@ -389,6 +391,7 @@ extern int pg_encoding_mbcliplen(int encoding, const char *mbstr,
extern int pg_mbcharcliplen(const char *mbstr, int len, int imit);
extern int pg_encoding_max_length(int encoding);
extern int pg_database_encoding_max_length(void);
extern mbcharacter_incrementer pg_database_encoding_character_incrementer(void);
extern int PrepareClientEncoding(int encoding);
extern int SetClientEncoding(int encoding);