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

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

2 files changed, 72 insertions, 1 deletions

diff --git a/src/test/regress/expected/bit.out b/src/test/regress/expected/bit.out
index 9c7d202149f..07491bb84ca 100644
--- a/src/test/regress/expected/bit.out
+++ b/src/test/regress/expected/bit.out
@@ -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
diff --git a/src/test/regress/sql/bit.sql b/src/test/regress/sql/bit.sql
index 419d47c8b75..cf2460b2122 100644
--- a/src/test/regress/sql/bit.sql
+++ b/src/test/regress/sql/bit.sql
@@ -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;