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Fix failure to zero-pad the result of bitshiftright().

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If the bitstring length is not a multiple of 8, we'd shift the
rightmost bits into the pad space, which must be zeroes --- bit_cmp,
for one, depends on that.  This'd lead to the result failing to
compare equal to what it should compare equal to, as reported in
bug #16013 from Daryl Waycott.

This is, if memory serves, not the first such bug in the bitstring
functions.  In hopes of making it the last one, do a bit more work
than minimally necessary to fix the bug:

* Add assertion checks to bit_out() and varbit_out() to complain if
they are given incorrectly-padded input.  This will improve the
odds that manual testing of any new patch finds problems.

* Encapsulate the padding-related logic in macros to make it
easier to use.

Also, remove unnecessary padding logic from bit_or() and bitxor().
Somebody had already noted that we need not re-pad the result of
bit_and() since the inputs are required to be the same length,
but failed to extrapolate that to the other two.

Also, move a comment block that once was near the head of varbit.c
(but people kept putting other stuff in front of it), to put it in
the header block.

Note for the release notes: if anyone has inconsistent data as a
result of saving the output of bitshiftright() in a table, it's
possible to fix it with something like
UPDATE mytab SET bitcol = ~(~bitcol) WHERE bitcol != ~(~bitcol);

This has been broken since day one, so back-patch to all supported
branches.

Discussion: https://postgr.es/m/16013-c2765b6996aacae9@postgresql.org
pull/47/head
Tom Lane 6 years ago
parent 0a2f894c3c
commit 5ac0d93600
4 changed files with 154 additions and 89 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 165
      src/backend/utils/adt/varbit.c
  2. 5
      src/include/utils/varbit.h
  3. 66
      src/test/regress/expected/bit.out
  4. 7
      src/test/regress/sql/bit.sql

165
src/backend/utils/adt/varbit.c
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@ -3,6 +3,21 @@
* varbit.c
* Functions for the SQL datatypes BIT() and BIT VARYING().
*
* The data structure contains the following elements:
* header -- length of the whole data structure (incl header)
* in bytes (as with all varying length datatypes)
* data section -- private data section for the bits data structures
* bitlength -- length of the bit string in bits
* bitdata -- bit string, most significant byte first
*
* The length of the bitdata vector should always be exactly as many
* bytes as are needed for the given bitlength. If the bitlength is
* not a multiple of 8, the extra low-order padding bits of the last
* byte must be zeroes.
*
* attypmod is defined as the length of the bit string in bits, or for
* varying bits the maximum length.
*
* Code originally contributed by Adriaan Joubert.
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
@ -27,6 +42,40 @@
#define HEXDIG(z) ((z)<10 ? ((z)+'0') : ((z)-10+'A'))
/* Mask off any bits that should be zero in the last byte of a bitstring */
#define VARBIT_PAD(vb) \
do { \
int32 pad_ = VARBITPAD(vb); \
Assert(pad_ >= 0 && pad_ < BITS_PER_BYTE); \
if (pad_ > 0) \
*(VARBITS(vb) + VARBITBYTES(vb) - 1) &= BITMASK << pad_; \
} while (0)
/*
* Many functions work byte-by-byte, so they have a pointer handy to the
* last-plus-one byte, which saves a cycle or two.
*/
#define VARBIT_PAD_LAST(vb, ptr) \
do { \
int32 pad_ = VARBITPAD(vb); \
Assert(pad_ >= 0 && pad_ < BITS_PER_BYTE); \
if (pad_ > 0) \
*((ptr) - 1) &= BITMASK << pad_; \
} while (0)
/* Assert proper padding of a bitstring */
#ifdef USE_ASSERT_CHECKING
#define VARBIT_CORRECTLY_PADDED(vb) \
do { \
int32 pad_ = VARBITPAD(vb); \
Assert(pad_ >= 0 && pad_ < BITS_PER_BYTE); \
Assert(pad_ == 0 || \
(*(VARBITS(vb) + VARBITBYTES(vb) - 1) & ~(BITMASK << pad_)) == 0); \
} while (0)
#else
#define VARBIT_CORRECTLY_PADDED(vb) ((void) 0)
#endif
static VarBit *bit_catenate(VarBit *arg1, VarBit *arg2);
static VarBit *bitsubstring(VarBit *arg, int32 s, int32 l,
bool length_not_specified);
@ -87,24 +136,6 @@ anybit_typmodout(int32 typmod)
}
/*----------
* attypmod -- contains the length of the bit string in bits, or for
* varying bits the maximum length.
*
* The data structure contains the following elements:
* header -- length of the whole data structure (incl header)
* in bytes. (as with all varying length datatypes)
* data section -- private data section for the bits data structures
* bitlength -- length of the bit string in bits
* bitdata -- bit string, most significant byte first
*
* The length of the bitdata vector should always be exactly as many
* bytes as are needed for the given bitlength. If the bitlength is
* not a multiple of 8, the extra low-order padding bits of the last
* byte must be zeroes.
*----------
*/
/*
* bit_in -
* converts a char string to the internal representation of a bitstring.
@ -264,6 +295,9 @@ bit_out(PG_FUNCTION_ARGS)
len,
bitlen;
/* Assertion to help catch any bit functions that don't pad correctly */
VARBIT_CORRECTLY_PADDED(s);
bitlen = VARBITLEN(s);
len = (bitlen + 3) / 4;
result = (char *) palloc(len + 2);
@ -304,8 +338,6 @@ bit_recv(PG_FUNCTION_ARGS)
VarBit *result;
int len,
bitlen;
int ipad;
bits8 mask;
bitlen = pq_getmsgint(buf, sizeof(int32));
if (bitlen < 0 || bitlen > VARBITMAXLEN)
@ -330,13 +362,8 @@ bit_recv(PG_FUNCTION_ARGS)
pq_copymsgbytes(buf, (char *) VARBITS(result), VARBITBYTES(result));
/* Make sure last byte is zero-padded if needed */
ipad = VARBITPAD(result);
if (ipad > 0)
{
mask = BITMASK << ipad;
*(VARBITS(result) + VARBITBYTES(result) - 1) &= mask;
}
/* Make sure last byte is correctly zero-padded */
VARBIT_PAD(result);
PG_RETURN_VARBIT_P(result);
}
@ -367,8 +394,6 @@ bit(PG_FUNCTION_ARGS)
bool isExplicit = PG_GETARG_BOOL(2);
VarBit *result;
int rlen;
int ipad;
bits8 mask;
/* No work if typmod is invalid or supplied data matches it already */
if (len <= 0 || len > VARBITMAXLEN || len == VARBITLEN(arg))
@ -394,12 +419,7 @@ bit(PG_FUNCTION_ARGS)
* if source data was shorter than target length (we assume the last byte
* of the source data was itself correctly zero-padded).
*/
ipad = VARBITPAD(result);
if (ipad > 0)
{
mask = BITMASK << ipad;
*(VARBITS(result) + VARBITBYTES(result) - 1) &= mask;
}
VARBIT_PAD(result);
PG_RETURN_VARBIT_P(result);
}
@ -574,6 +594,9 @@ varbit_out(PG_FUNCTION_ARGS)
k,
len;
/* Assertion to help catch any bit functions that don't pad correctly */
VARBIT_CORRECTLY_PADDED(s);
len = VARBITLEN(s);
result = (char *) palloc(len + 1);
sp = VARBITS(s);
@ -620,8 +643,6 @@ varbit_recv(PG_FUNCTION_ARGS)
VarBit *result;
int len,
bitlen;
int ipad;
bits8 mask;
bitlen = pq_getmsgint(buf, sizeof(int32));
if (bitlen < 0 || bitlen > VARBITMAXLEN)
@ -646,13 +667,8 @@ varbit_recv(PG_FUNCTION_ARGS)
pq_copymsgbytes(buf, (char *) VARBITS(result), VARBITBYTES(result));
/* Make sure last byte is zero-padded if needed */
ipad = VARBITPAD(result);
if (ipad > 0)
{
mask = BITMASK << ipad;
*(VARBITS(result) + VARBITBYTES(result) - 1) &= mask;
}
/* Make sure last byte is correctly zero-padded */
VARBIT_PAD(result);
PG_RETURN_VARBIT_P(result);
}
@ -729,8 +745,6 @@ varbit(PG_FUNCTION_ARGS)
bool isExplicit = PG_GETARG_BOOL(2);
VarBit *result;
int rlen;
int ipad;
bits8 mask;
/* No work if typmod is invalid or supplied data matches it already */
if (len <= 0 || len >= VARBITLEN(arg))
@ -749,13 +763,8 @@ varbit(PG_FUNCTION_ARGS)
memcpy(VARBITS(result), VARBITS(arg), VARBITBYTES(result));
/* Make sure last byte is zero-padded if needed */
ipad = VARBITPAD(result);
if (ipad > 0)
{
mask = BITMASK << ipad;
*(VARBITS(result) + VARBITBYTES(result) - 1) &= mask;
}
/* Make sure last byte is correctly zero-padded */
VARBIT_PAD(result);
PG_RETURN_VARBIT_P(result);
}
@ -1013,6 +1022,8 @@ bit_catenate(VarBit *arg1, VarBit *arg2)
}
}
/* The pad bits should be already zero at this point */
return result;
}
@ -1046,14 +1057,12 @@ bitsubstring(VarBit *arg, int32 s, int32 l, bool length_not_specified)
int bitlen,
rbitlen,
len,
ipad = 0,
ishift,
i;
int e,
s1,
e1;
bits8 mask,
*r,
bits8 *r,
*ps;
bitlen = VARBITLEN(arg);
@ -1118,13 +1127,9 @@ bitsubstring(VarBit *arg, int32 s, int32 l, bool length_not_specified)
r++;
}
}
/* Do we need to pad at the end? */
ipad = VARBITPAD(result);
if (ipad > 0)
{
mask = BITMASK << ipad;
*(VARBITS(result) + len - 1) &= mask;
}
/* Make sure last byte is correctly zero-padded */
VARBIT_PAD(result);
}
return result;
@ -1246,7 +1251,7 @@ bit_and(PG_FUNCTION_ARGS)
for (i = 0; i < VARBITBYTES(arg1); i++)
*r++ = *p1++ & *p2++;
/* Padding is not needed as & of 0 pad is 0 */
/* Padding is not needed as & of 0 pads is 0 */
PG_RETURN_VARBIT_P(result);
}
@ -1268,7 +1273,6 @@ bit_or(PG_FUNCTION_ARGS)
bits8 *p1,
*p2,
*r;
bits8 mask;
bitlen1 = VARBITLEN(arg1);
bitlen2 = VARBITLEN(arg2);
@ -1287,13 +1291,7 @@ bit_or(PG_FUNCTION_ARGS)
for (i = 0; i < VARBITBYTES(arg1); i++)
*r++ = *p1++ | *p2++;
/* Pad the result */
mask = BITMASK << VARBITPAD(result);
if (mask)
{
r--;
*r &= mask;
}
/* Padding is not needed as | of 0 pads is 0 */
PG_RETURN_VARBIT_P(result);
}
@ -1315,7 +1313,6 @@ bitxor(PG_FUNCTION_ARGS)
bits8 *p1,
*p2,
*r;
bits8 mask;
bitlen1 = VARBITLEN(arg1);
bitlen2 = VARBITLEN(arg2);
@ -1335,13 +1332,7 @@ bitxor(PG_FUNCTION_ARGS)
for (i = 0; i < VARBITBYTES(arg1); i++)
*r++ = *p1++ ^ *p2++;
/* Pad the result */
mask = BITMASK << VARBITPAD(result);
if (mask)
{
r--;
*r &= mask;
}
/* Padding is not needed as ^ of 0 pads is 0 */
PG_RETURN_VARBIT_P(result);
}
@ -1357,7 +1348,6 @@ bitnot(PG_FUNCTION_ARGS)
VarBit *result;
bits8 *p,
*r;
bits8 mask;
result = (VarBit *) palloc(VARSIZE(arg));
SET_VARSIZE(result, VARSIZE(arg));
@ -1368,13 +1358,8 @@ bitnot(PG_FUNCTION_ARGS)
for (; p < VARBITEND(arg); p++)
*r++ = ~*p;
/* Pad the result */
mask = BITMASK << VARBITPAD(result);
if (mask)
{
r--;
*r &= mask;
}
/* Must zero-pad the result, because extra bits are surely 1's here */
VARBIT_PAD_LAST(result, r);
PG_RETURN_VARBIT_P(result);
}
@ -1441,6 +1426,8 @@ bitshiftleft(PG_FUNCTION_ARGS)
*r = 0;
}
/* The pad bits should be already zero at this point */
PG_RETURN_VARBIT_P(result);
}
@ -1507,6 +1494,8 @@ bitshiftright(PG_FUNCTION_ARGS)
if ((++r) < VARBITEND(result))
*r = (*p << (BITS_PER_BYTE - ishift)) & BITMASK;
}
/* We may have shifted 1's into the pad bits, so fix that */
VARBIT_PAD_LAST(result, r);
}
PG_RETURN_VARBIT_P(result);

5
src/include/utils/varbit.h
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@ -21,6 +21,11 @@
/*
* Modeled on struct varlena from postgres.h, but data type is bits8.
*
* Caution: if bit_len is not a multiple of BITS_PER_BYTE, the low-order
* bits of the last byte of bit_dat[] are unused and MUST be zeroes.
* (This allows bit_cmp() to not bother masking the last byte.)
* Also, there should not be any excess bytes counted in the header length.
*/
typedef struct
{

66
src/test/regress/expected/bit.out
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@ -477,6 +477,50 @@ SELECT POSITION(B'1101' IN b),
0 | 0 | 0000000000000001
(16 rows)
SELECT b, b >> 1 AS bsr, b << 1 AS bsl
FROM BIT_SHIFT_TABLE ;
b | bsr | bsl
------------------+------------------+------------------
1101100000000000 | 0110110000000000 | 1011000000000000
0110110000000000 | 0011011000000000 | 1101100000000000
0011011000000000 | 0001101100000000 | 0110110000000000
0001101100000000 | 0000110110000000 | 0011011000000000
0000110110000000 | 0000011011000000 | 0001101100000000
0000011011000000 | 0000001101100000 | 0000110110000000
0000001101100000 | 0000000110110000 | 0000011011000000
0000000110110000 | 0000000011011000 | 0000001101100000
0000000011011000 | 0000000001101100 | 0000000110110000
0000000001101100 | 0000000000110110 | 0000000011011000
0000000000110110 | 0000000000011011 | 0000000001101100
0000000000011011 | 0000000000001101 | 0000000000110110
0000000000001101 | 0000000000000110 | 0000000000011010
0000000000000110 | 0000000000000011 | 0000000000001100
0000000000000011 | 0000000000000001 | 0000000000000110
0000000000000001 | 0000000000000000 | 0000000000000010
(16 rows)
SELECT b::bit(15), b::bit(15) >> 1 AS bsr, b::bit(15) << 1 AS bsl
FROM BIT_SHIFT_TABLE ;
b | bsr | bsl
-----------------+-----------------+-----------------
110110000000000 | 011011000000000 | 101100000000000
011011000000000 | 001101100000000 | 110110000000000
001101100000000 | 000110110000000 | 011011000000000
000110110000000 | 000011011000000 | 001101100000000
000011011000000 | 000001101100000 | 000110110000000
000001101100000 | 000000110110000 | 000011011000000
000000110110000 | 000000011011000 | 000001101100000
000000011011000 | 000000001101100 | 000000110110000
000000001101100 | 000000000110110 | 000000011011000
000000000110110 | 000000000011011 | 000000001101100
000000000011011 | 000000000001101 | 000000000110110
000000000001101 | 000000000000110 | 000000000011010
000000000000110 | 000000000000011 | 000000000001100
000000000000011 | 000000000000001 | 000000000000110
000000000000001 | 000000000000000 | 000000000000010
000000000000000 | 000000000000000 | 000000000000000
(16 rows)
CREATE TABLE VARBIT_SHIFT_TABLE(v BIT VARYING(20));
INSERT INTO VARBIT_SHIFT_TABLE VALUES (B'11011');
INSERT INTO VARBIT_SHIFT_TABLE SELECT CAST(v || B'0' AS BIT VARYING(6)) >>1 FROM VARBIT_SHIFT_TABLE;
@ -507,6 +551,28 @@ SELECT POSITION(B'1101' IN v),
16 | 16 | 00000000000000011011
(16 rows)
SELECT v, v >> 1 AS vsr, v << 1 AS vsl
FROM VARBIT_SHIFT_TABLE ;
v | vsr | vsl
----------------------+----------------------+----------------------
11011 | 01101 | 10110
011011 | 001101 | 110110
0011011 | 0001101 | 0110110
00011011 | 00001101 | 00110110
000011011 | 000001101 | 000110110
0000011011 | 0000001101 | 0000110110
00000011011 | 00000001101 | 00000110110
000000011011 | 000000001101 | 000000110110
0000000011011 | 0000000001101 | 0000000110110
00000000011011 | 00000000001101 | 00000000110110
000000000011011 | 000000000001101 | 000000000110110
0000000000011011 | 0000000000001101 | 0000000000110110
00000000000011011 | 00000000000001101 | 00000000000110110
000000000000011011 | 000000000000001101 | 000000000000110110
0000000000000011011 | 0000000000000001101 | 0000000000000110110
00000000000000011011 | 00000000000000001101 | 00000000000000110110
(16 rows)
DROP TABLE BIT_SHIFT_TABLE;
DROP TABLE VARBIT_SHIFT_TABLE;
-- Get/Set bit

7
src/test/regress/sql/bit.sql
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@ -168,6 +168,10 @@ SELECT POSITION(B'1101' IN b),
POSITION(B'11011' IN b),
b
FROM BIT_SHIFT_TABLE ;
SELECT b, b >> 1 AS bsr, b << 1 AS bsl
FROM BIT_SHIFT_TABLE ;
SELECT b::bit(15), b::bit(15) >> 1 AS bsr, b::bit(15) << 1 AS bsl
FROM BIT_SHIFT_TABLE ;
CREATE TABLE VARBIT_SHIFT_TABLE(v BIT VARYING(20));
@ -180,7 +184,8 @@ SELECT POSITION(B'1101' IN v),
POSITION(B'11011' IN v),
v
FROM VARBIT_SHIFT_TABLE ;
SELECT v, v >> 1 AS vsr, v << 1 AS vsl
FROM VARBIT_SHIFT_TABLE ;
DROP TABLE BIT_SHIFT_TABLE;
DROP TABLE VARBIT_SHIFT_TABLE;

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