Re: Re: BIT/BIT VARYING status

Are there any open items related to the BIT type?

> Tom Lane wrote:
> >
> > I have made a first cut at completing integration of Adriaan Joubert's
> > BIT code into the backend. There are a couple little things left to
> > do (for example, scalarltsel doesn't know what to do with BIT values)
> > as well as some not-so-little things:
> >
> > 1. SQL92 mentions a bitwise position function, which we do not have.
>
> Sorry, I have been very busy, so only got down to implementing a
> position function last night. It's a bit messy (lots of masks and
> bit-twiddling), but I feel fairly happy now that it is doing the right
> thing. I tested it with my own loadable types, as the integration into
> postgres proper stumped my somewhat. The next oid up for a bit function
> is in use already. Anyway, the patches are attached, and I'm hoping that
> some friendly sole will integrate the new position function into
> postgres proper.
>
> > 2. We don't handle <bit string> and <hex string> literals correctly;
> > the scanner converts them into integers which seems quite at variance
> > with the spec's semantics.
>
> This is still a problem that needs to be fixed. Also, it the parser did
> not seem to be too happy about the 'position' syntax, but I may have it
> wrong of course. I don;t know how to attach the position function to a
> piece of syntax such as (position <substr> in <field>) either, so I'm
> hoping that somebody can pick this up.
>
> Also, i have started putting together a file for regression testing. I
> noticed that the substring syntax does not seem to work:
>
> SELECT SUBSTRING(b FROM 2 FOR 4)
> FROM ZPBIT_TABLE;
>
> gives:
>
> ERROR: Function 'substr(bit, int4, int4)' does not exist
> Unable to identify a function that satisfies the given argument
> types
> You may need to add explicit typecasts
>
> and similar for a varying bit argument.
>
> If somebody with better knowledge of postgres could do the integration,
> please, I will finish off a regression test.
>
> Thanks!
>
> Adriaan

> *** src/backend/utils/adt/varbit.c.old Sun Oct 29 11:05:11 2000
> --- src/backend/utils/adt/varbit.c Mon Oct 30 04:58:35 2000
> ***************
> *** 1053,1060 ****
> /* Negative shift is a shift to the left */
> if (shft < 0)
> PG_RETURN_DATUM(DirectFunctionCall2(bitshiftleft,
> ! VarBitPGetDatum(arg),
> ! Int32GetDatum(-shft)));
>
> result = (VarBit *) palloc(VARSIZE(arg));
> VARATT_SIZEP(result) = VARSIZE(arg);
> --- 1053,1060 ----
> /* Negative shift is a shift to the left */
> if (shft < 0)
> PG_RETURN_DATUM(DirectFunctionCall2(bitshiftleft,
> ! VarBitPGetDatum(arg),
> ! Int32GetDatum(-shft)));
>
> result = (VarBit *) palloc(VARSIZE(arg));
> VARATT_SIZEP(result) = VARSIZE(arg);
> ***************
> *** 1145,1148 ****
> --- 1145,1242 ----
> result >>= VARBITPAD(arg);
>
> PG_RETURN_INT32(result);
> + }
> +
> + /* Determines the position of S1 in the bitstring S2 (1-based string).
> + * If S1 does not appear in S2 this function returns 0.
> + * If S1 is of length 0 this function returns 1.
> + */
> + Datum
> + bitposition(PG_FUNCTION_ARGS)
> + {
> + VarBit *substr = PG_GETARG_VARBIT_P(0);
> + VarBit *arg = PG_GETARG_VARBIT_P(1);
> + int substr_length,
> + arg_length,
> + i,
> + is;
> + bits8 *s, /* pointer into substring */
> + *p; /* pointer into arg */
> + bits8 cmp, /* shifted substring byte to compare */
> + mask1, /* mask for substring byte shifted right */
> + mask2, /* mask for substring byte shifted left */
> + end_mask, /* pad mask for last substring byte */
> + arg_mask; /* pad mask for last argument byte */
> + bool is_match;
> +
> + /* Get the substring length */
> + substr_length = VARBITLEN(substr);
> + arg_length = VARBITLEN(arg);
> +
> + /* Argument has 0 length or substring longer than argument, return 0 */
> + if (arg_length == 0 || substr_length > arg_length)
> + PG_RETURN_INT32(0);
> +
> + /* 0-length means return 1 */
> + if (substr_length == 0)
> + PG_RETURN_INT32(1);
> +
> + /* Initialise the padding masks */
> + end_mask = BITMASK << VARBITPAD(substr);
> + arg_mask = BITMASK << VARBITPAD(arg);
> + for (i = 0; i < VARBITBYTES(arg) - VARBITBYTES(substr) + 1; i++)
> + {
> + for (is = 0; is < BITS_PER_BYTE; is++) {
> + is_match = true;
> + p = VARBITS(arg) + i;
> + mask1 = BITMASK >> is;
> + mask2 = ~mask1;
> + for (s = VARBITS(substr);
> + is_match && s < VARBITEND(substr); s++)
> + {
> + cmp = *s >> is;
> + if (s == VARBITEND(substr) - 1)
> + {
> + mask1 &= end_mask >> is;
> + if (p == VARBITEND(arg) - 1) {
> + /* Check that there is enough of arg left */
> + if (mask1 & ~arg_mask) {
> + is_match = false;
> + break;
> + }
> + mask1 &= arg_mask;
> + }
> + }
> + is_match = ((cmp ^ *p) & mask1) == 0;
> + if (!is_match)
> + break;
> + // Move on to the next byte
> + p++;
> + if (p == VARBITEND(arg)) {
> + mask2 = end_mask << (BITS_PER_BYTE - is);
> + is_match = mask2 == 0;
> + elog(NOTICE,"S. %d %d em=%2x sm=%2x r=%d",
> + i,is,end_mask,mask2,is_match);
> + break;
> + }
> + cmp = *s << (BITS_PER_BYTE - is);
> + if (s == VARBITEND(substr) - 1)
> + {
> + mask2 &= end_mask << (BITS_PER_BYTE - is);
> + if (p == VARBITEND(arg) - 1) {
> + if (mask2 & ~arg_mask) {
> + is_match = false;
> + break;
> + }
> + mask2 &= arg_mask;
> + }
> + }
> + is_match = ((cmp ^ *p) & mask2) == 0;
> + }
> + /* Have we found a match */
> + if (is_match)
> + PG_RETURN_INT32(i*BITS_PER_BYTE + is + 1);
> + }
> + }
> + PG_RETURN_INT32(0);
> }

> *** src/include/utils/varbit.h.old Sun Oct 29 11:04:58 2000
> --- src/include/utils/varbit.h Sun Oct 29 11:05:58 2000
> ***************
> *** 87,91 ****
> --- 87,92 ----
> extern Datum bitoctetlength(PG_FUNCTION_ARGS);
> extern Datum bitfromint4(PG_FUNCTION_ARGS);
> extern Datum bittoint4(PG_FUNCTION_ARGS);
> + extern Datum bitposition(PG_FUNCTION_ARGS);
>
> #endif

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026