Attached are the C-routines that implement a BIT and BIT VARYING type.

Adriaan Joubert

1 files changed, 832 insertions, 0 deletions

diff --git a/contrib/bit/varbit.c b/contrib/bit/varbit.c
new file mode 100644
index 00000000000..257f9766fd6
--- /dev/null
+++ b/contrib/bit/varbit.c
@@ -0,0 +1,832 @@
+/*-------------------------------------------------------------------------
+ *
+ * varbit.c
+ *	  Functions for the built-in type bit() and varying bit().
+ *
+ * IDENTIFICATION
+ *	  $Header: /cvsroot/pgsql/contrib/bit/Attic/varbit.c,v 1.1 1999/11/29 22:34:36 momjian Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+#include "varbit.h"
+/*
+#include "access/htup.h"
+#include "catalog/pg_type.h"
+#include "utils/builtins.h"
+*/
+
+
+
+/* 
+   Prefixes:
+     zp    -- zero-padded fixed length bit string
+     var   -- varying bit string
+
+   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 -- lenght of the bit string in bits
+	 bitdata   -- least significant byte first string
+*/
+
+/*
+ * zpbitin -
+
+ *	  converts a string to the internal representation of a bitstring.
+ *        The length is determined by the number of bits required plus
+ *        VARHDRSZ bytes or from atttypmod. 
+ *	  (XXX dummy is here because we pass typelem as the second argument 
+ *        for array_in. copied this, no idea what it means??)
+ */
+char *
+zpbitin(char *s, int dummy,  int32 atttypmod)
+{
+  char *result, 
+    *sp;		/* pointer into the character string  */
+  bits8 *r;
+  int len,		/* Length of the whole data structure */
+    bitlen,		/* Number of bits in the bit string   */
+    slen;		/* Length of the input string         */
+  int bit_not_hex;      /* 0 = hex string  1=bit string       */
+  int i, bc, ipad;
+  bits8 x, y;
+
+
+  if (s == NULL)
+    return NULL;
+
+  /* Check that the first character is a b or an x */
+  if (s[0]=='b' || s[0]=='B') 
+      bit_not_hex = 1;
+  else if (s[0]=='x' || s[0]=='X') 
+      bit_not_hex = 0;
+  else 
+    elog(ERROR, "zpbitin: %s is not a valid bitstring",s);
+
+  slen = strlen(s) - 1;
+  /* Determine bitlength from input string */
+  bitlen = slen;
+  if (!bit_not_hex)
+    bitlen *= 4;
+  
+  /* Sometimes atttypmod is not supplied. If it is supplied we need to make
+     sure that the bitstring fits. Note that the number of infered bits can
+     be larger than the number of actual bits needed, but only if we are 
+     reading a hex string and not by more than 3 bits, as a hex string gives 
+     and accurate length upto 4 bits */
+  if (atttypmod == -1)
+    atttypmod = bitlen;
+  else
+    if (bitlen>atttypmod && bit_not_hex || bitlen>atttypmod+3 && !bit_not_hex)
+	  elog(ERROR, "zpbitin: bit string of size %d cannot be written into bits(%d)",
+	       bitlen,atttypmod);
+
+
+  len = VARBITDATALEN(atttypmod);
+
+  if (len > MaxAttrSize)
+    elog(ERROR, "zpbitin: length of bit() must be less than %d",
+	 (MaxAttrSize-VARHDRSZ-VARBITHDRSZ)*BITSPERBYTE);
+
+  result = (char *) palloc(len);
+  /* set to 0 so that *r is always initialised and strin is zero-padded */
+  memset(result, 0, len);
+  VARSIZE(result) = len;
+  VARBITLEN(result) = atttypmod;
+
+  /* We need to read the bitstring from the end, as we store it least 
+     significant byte first. s points to the byte before the beginning
+     of the bitstring */
+  sp = s+1;
+  r = (bits8 *) VARBITS(result);
+  if (bit_not_hex) 
+    {
+      /* Parse the bit representation of the string */
+      /* We know it fits, as bitlen was compared to atttypmod */
+      x = BITHIGH;
+      for (bc = 0; sp != s+slen+1; sp++, bc++)
+	{
+	  if (*sp=='1')
+	    *r |= x;
+	  if (bc==7) {
+	    bc = 0;
+	    x = BITHIGH;
+	    r++;
+	  } else 
+	    x >>= 1;
+	}
+     }
+  else 
+    {
+      /* Parse the hex representation of the string */
+      for (bc = 0; sp != s+slen+1; sp++)
+	{
+	  if (*sp>='0' && *sp<='9') 
+	    x = (bits8) (*sp - '0');
+	  else if (*sp>='A' && *sp<='F') 
+	    x = (bits8) (*sp - 'A') + 10;
+	  else if (*sp>='a' && *sp<='f') 
+	    x = (bits8) (*sp - 'a') + 10;
+	  else 
+	    elog(ERROR,"Cannot parse %c as a hex digit",*sp);
+	  if (bc) {
+	    bc = 0;
+	    *r++ |= x;
+	  } else {
+	    bc++;
+	    *r = x<<4;
+	  }
+	}
+    }
+
+  if (bitlen > atttypmod) {
+    /* Check that this fitted */
+    r = (bits8 *) (result + len - 1);
+    ipad = VARBITPAD(result);
+    /* The bottom ipad bits of the byte pointed to by r need to be zero */
+    /*    printf("Byte %X  shift %X %d\n",*r,(*r << (8-ipad)) & BITMASK,
+	   (*r << (8-ipad)) & BITMASK > 0);
+    */
+    if (((*r << (BITSPERBYTE-ipad)) & BITMASK) > 0)
+      elog(ERROR, "zpbitin: bit string too large for bit(%d) data type",
+	   atttypmod);
+  }
+
+  return result;
+}
+
+/* zpbitout -
+ *    for the time being we print everything as hex strings, as this is likely 
+ *    to be more compact than bit strings, and consequently much more efficient
+ *    for long strings
+ */
+char *
+zpbitout(char *s)
+{
+  char	   *result, *r;
+  VarBit   sp;
+  int	   i, len, bitlen;
+  
+  if (s == NULL)
+    {
+      result = (char *) palloc(2);
+      result[0] = '-';
+      result[1] = '\0';
+    }
+  else
+    {
+      bitlen = VARBITLEN(s);
+      len = bitlen/4 + (bitlen%4>0 ? 1 : 0);
+      result = (char *) palloc(len + 4);
+      sp = (bits8 *) VARBITS(s);
+      r = result;
+      *r++ = 'X';
+      *r++ = '\'';
+      /* we cheat by knowing that we store full bytes zero padded */
+      for (i=0; i<len; i+=2, sp++) {
+	*r++ = HEXDIG((*sp)>>4);
+	*r++ = HEXDIG((*sp) & 0xF);
+      }
+      /* Go back one step if we printed a hex number that was not part
+	 of the bitstring anymore */
+      if (i==len+1)
+	r--;
+      *r++ = '\'';
+      *r = '\0';
+    }
+  return result;
+}
+
+/* zpbitsout -
+ *    Prints the string a bits
+ */
+char *
+zpbitsout(char *s)
+{
+  char	   *result, *r;
+  VarBit   sp;
+  bits8    x;
+  int	   i, k, len;
+  
+  if (s == NULL)
+    {
+      result = (char *) palloc(2);
+      result[0] = '-';
+      result[1] = '\0';
+    }
+  else
+    {
+      len = VARBITLEN(s);
+      result = (char *) palloc(len + 4);
+      sp = (bits8 *) VARBITS(s);
+      r = result;
+      *r++ = 'B';
+      *r++ = '\'';
+      for (i=0; i<len-BITSPERBYTE; i+=BITSPERBYTE, sp++) {
+	x = *sp;
+	for (k=0; k<BITSPERBYTE; k++) 
+	  {
+	    *r++ = (x & BITHIGH) ? '1' : '0';
+	    x <<= 1;
+	  }
+      }
+      x = *sp;
+      for (k=i; k<len; k++)
+	{
+	  *r++ = (x & BITHIGH) ? '1' : '0';
+	  x <<= 1;
+	}
+      *r++ = '\'';
+      *r = '\0';
+    }
+  return result;
+}
+
+
+/*
+ * varbitin -
+ *	  converts a string to the internal representation of a bitstring.
+*/
+char *
+varbitin(char *s, int dummy,  int32 atttypmod)
+{
+  char *result, 
+    *sp;		/* pointer into the character string  */
+  bits8 *r;
+  int len,		/* Length of the whole data structure */
+    bitlen,		/* Number of bits in the bit string   */
+    slen;		/* Length of the input string         */
+  int bit_not_hex;
+  int i, bc, ipad;
+  bits8 x, y;
+
+
+  if (s == NULL)
+    return NULL;
+
+  /* Check that the first character is a b or an x */
+  if (s[0]=='b' || s[0]=='B') 
+      bit_not_hex = 1;
+  else if (s[0]=='x' || s[0]=='X') 
+      bit_not_hex = 0;
+  else 
+    elog(ERROR, "zpbitin: %s is not a valid bitstring",s);
+
+  slen = strlen(s) - 1;
+  /* Determine bitlength from input string */
+  bitlen = slen;
+  if (!bit_not_hex)
+    bitlen *= 4;
+  
+  /* Sometimes atttypmod is not supplied. If it is supplied we need to make
+     sure that the bitstring fits. Note that the number of infered bits can
+     be larger than the number of actual bits needed, but only if we are 
+     reading a hex string and not by more than 3 bits, as a hex string gives 
+     and accurate length upto 4 bits */
+  if (atttypmod > -1)
+    if (bitlen>atttypmod && bit_not_hex || bitlen>atttypmod+3 && !bit_not_hex)
+	  elog(ERROR, "varbitin: bit string of size %d cannot be written into varying bits(%d)",
+	       bitlen,atttypmod);
+
+
+  len = VARBITDATALEN(bitlen);
+
+  if (len > MaxAttrSize)
+    elog(ERROR, "varbitin: length of bit() must be less than %d",
+	 (MaxAttrSize-VARHDRSZ-VARBITHDRSZ)*BITSPERBYTE);
+
+  result = (char *) palloc(len);
+  /* set to 0 so that *r is always initialised and strin is zero-padded */
+  memset(result, 0, len);
+  VARSIZE(result) = len;
+  VARBITLEN(result) = bitlen;
+
+  /* We need to read the bitstring from the end, as we store it least 
+     significant byte first. s points to the byte before the beginning
+     of the bitstring */
+  sp = s + 1;
+  r = (VarBit) VARBITS(result);
+  if (bit_not_hex) 
+    {
+      /* Parse the bit representation of the string */
+      x = BITHIGH;
+      for (bc = 0; sp != s+slen+1; sp++, bc++)
+	{
+	  if (*sp=='1')
+	    *r |= x;
+	  if (bc==7) {
+	    bc = 0;
+	    x = BITHIGH;
+	    r++;
+	  } else 
+	    x >>= 1;
+	}
+     }
+  else 
+    {
+      for (bc = 0; sp != s+slen+1; sp++)
+	{
+	  if (*sp>='0' && *sp<='9') 
+	    x = (bits8) (*sp - '0');
+	  else if (*sp>='A' && *sp<='F') 
+	    x = (bits8) (*sp - 'A') + 10;
+	  else if (*sp>='a' && *sp<='f') 
+	    x = (bits8) (*sp - 'a') + 10;
+	  else 
+	    elog(ERROR,"Cannot parse %c as a hex digit",*sp);
+	  if (bc) {
+	    bc = 0;
+	    *r++ |= x;
+	  } else {
+	    bc++;
+	    *r = x<<4;
+	  }
+	}
+    }
+
+  if (bitlen > atttypmod) {
+    /* Check that this fitted */
+    r = (bits8 *) (result + len - 1);
+    ipad = VARBITPAD(result);
+    /* The bottom ipad bits of the byte pointed to by r need to be zero */
+    if (((*r << (BITSPERBYTE-ipad)) & BITMASK) > 0)
+      elog(ERROR, "varbitin: bit string too large for varying bit(%d) data type",
+	   atttypmod);
+  }
+
+  return result;
+}
+
+/*
+  the zpbitout routines are fine for varying bits as well 
+*/
+
+
+/*
+ * Comparison operators
+ *
+ * We only need one set of comparison operators for bitstrings, as the lengths
+ * are stored in the same way for zero-padded and varying bit strings. 
+ *
+ * Note that the standard is not unambiguous about the comparison between 
+ * zero-padded bit strings and varying bitstrings. If the same value is written
+ * into a zero padded bitstring as into a varying bitstring, but the zero 
+ * padded bitstring has greater length, it will be bigger. 
+ *
+ * Zeros from the beginning of a bitstring cannot simply be ignored, as they
+ * may be part of a bit string and may be significant.
+ */
+
+bool
+biteq (char *arg1, char *arg2)
+{
+  int bitlen1,
+    bitlen2;
+  bits8 *p1, *p2;
+
+  if (!PointerIsValid(arg1) || !PointerIsValid(arg2))
+    return (bool) 0;
+  bitlen1 = VARBITLEN(arg1);
+  bitlen2 = VARBITLEN(arg2);
+  if (bitlen1 != bitlen2)
+    return (bool) 0;
+  
+  /* bit strings are always stored in a full number of bytes */
+  return memcmp((void *)VARBITS(arg1),(void *)VARBITS(arg2),
+		VARBITBYTES(arg1)) == 0;
+}
+
+bool
+bitne (char *arg1, char *arg2)
+{
+  int bitlen1,
+    bitlen2;
+  bits8 *p1, *p2;
+
+  if (!PointerIsValid(arg1) || !PointerIsValid(arg2))
+    return (bool) 0;
+  bitlen1 = VARBITLEN(arg1);
+  bitlen2 = VARBITLEN(arg2);
+  if (bitlen1 != bitlen2)
+    return (bool) 1;
+  
+  /* bit strings are always stored in a full number of bytes */
+  return memcmp((void *)VARBITS(arg1),(void *)VARBITS(arg2),
+		VARBITBYTES(arg1)) != 0;
+}
+
+/* bitcmp
+ * 
+ * Compares two bitstrings and returns -1, 0, 1 depending on whether the first
+ * string is smaller, equal, or bigger than the second. All bits are considered
+ * and additional zero bits may make one string smaller/larger than the other,
+ * even if their zero-padded values would be the same.
+ *   Anything is equal to undefined.
+ */
+int 
+bitcmp (char *arg1, char *arg2)
+{
+  int bitlen1, bytelen1,
+    bitlen2, bytelen2;
+  bits8 *p1, *p2;
+  int cmp;
+
+  if (!PointerIsValid(arg1) || !PointerIsValid(arg2))
+    return (bool) 0;
+  bytelen1 = VARBITBYTES(arg1);  
+  bytelen2 = VARBITBYTES(arg2);
+  
+  cmp = memcmp(VARBITS(arg1),VARBITS(arg2),Min(bytelen1,bytelen2));
+  if (cmp==0) {
+    bitlen1 = VARBITLEN(arg1);
+    bitlen2 = VARBITLEN(arg2);
+    if (bitlen1 != bitlen2) 
+      return bitlen1 < bitlen2 ? -1 : 1;
+  }
+  return cmp;
+}
+
+bool
+bitlt (char *arg1, char *arg2)
+{
+  return (bool) (bitcmp(arg1,arg2) == -1);
+}
+
+bool
+bitle (char *arg1, char *arg2)
+{
+  return (bool) (bitcmp(arg1,arg2) <= 0);
+}
+
+bool
+bitge (char *arg1, char *arg2)
+{
+  return (bool) (bitcmp(arg1,arg2) >= 0);
+}
+
+bool
+bitgt (char *arg1, char *arg2)
+{
+  return (bool) (bitcmp(arg1,arg2) == 1);
+}
+
+/* bitcat
+ * Concatenation of bit strings
+ */
+char *
+bitcat (char *arg1, char *arg2)
+{
+  int bitlen1, bitlen2, bytelen, bit1pad, bit2shift;
+  char *result;
+  bits8 *pr, *pa;
+
+  if (!PointerIsValid(arg1) || !PointerIsValid(arg2))
+    return NULL;
+
+  bitlen1 = VARBITLEN(arg1);
+  bitlen2 = VARBITLEN(arg2);
+
+  bytelen = VARBITDATALEN(bitlen1+bitlen2);
+  
+  result = (char *) palloc(bytelen*sizeof(bits8));
+  VARSIZE(result) = bytelen;
+  VARBITLEN(result) = bitlen1+bitlen2;
+  printf("%d %d %d \n",VARBITBYTES(arg1),VARBITLEN(arg1),VARBITPAD(arg1));
+  /* Copy the first bitstring in */
+  memcpy(VARBITS(result),VARBITS(arg1),VARBITBYTES(arg1));
+  /* Copy the second bit string */
+  bit1pad = VARBITPAD(arg1);
+  if (bit1pad==0) 
+    {
+      memcpy(VARBITS(result)+VARBITBYTES(arg1),VARBITS(arg2),
+	     VARBITBYTES(arg2));
+    }
+  else if (bitlen2>0)
+    {
+      /* We need to shift all the results to fit */
+      bit2shift = BITSPERBYTE - bit1pad;
+      pa = (VarBit) VARBITS(arg2);
+      pr = (VarBit) VARBITS(result)+VARBITBYTES(arg1)-1;
+      for ( ; pa < VARBITEND(arg2); pa++) {
+	*pr = *pr | ((*pa >> bit2shift) & BITMASK);
+	pr++;
+	if (pr < VARBITEND(result))
+	  *pr = (*pa << bit1pad) & BITMASK;
+      }
+    }
+
+  return result;
+}
+
+/* bitsubstr
+ * retrieve a substring from the bit string. 
+ * Note, s is 1-based.
+ * SQL draft 6.10 9)
+ */
+char * 
+bitsubstr (char *arg, int32 s, int32 l)
+{
+  int bitlen,
+    rbitlen,
+    len,
+    ipad,
+    ishift,
+    i;
+  int e, s1, e1;
+  char * result;
+  bits8 mask, *r, *ps;
+
+  if (!PointerIsValid(arg))
+    return NULL;
+
+  bitlen = VARBITLEN(arg);
+  e = s+l;
+  s1 = Max(s,1);
+  e1 = Min(e,bitlen+1);
+  if (s1>bitlen || e1<1) 
+    {
+      /* Need to return a null string */
+      len = VARBITDATALEN(0);
+      result = (char *) palloc(len);
+      VARBITLEN(result) = 0;
+      VARSIZE(result) = len;
+    } 
+  else 
+    {
+      /* OK, we've got a true substring starting at position s1-1 and 
+	 ending at position e1-1 */
+      rbitlen = e1-s1;
+      len = VARBITDATALEN(rbitlen);
+      result = (char *) palloc(len);
+      VARBITLEN(result) = rbitlen;
+      VARSIZE(result) = len;
+      /* Are we copying from a byte boundary? */
+      if ((s1-1)%BITSPERBYTE==0) 
+	{
+	  /* Yep, we are copying bytes */
+	  len -= VARHDRSZ + VARBITHDRSZ;
+	  memcpy(VARBITS(result),VARBITS(arg)+(s1-1)/BITSPERBYTE,len);
+	} 
+      else 
+	{
+	  /* Figure out how much we need to shift the sequence by */
+	  ishift = (s1-1)%BITSPERBYTE;
+	  r = (VarBit) VARBITS(result);
+	  ps = (VarBit) VARBITS(arg) + (s1-1)/BITSPERBYTE;
+	  for (i=0; i<len; i++) 
+	    {
+	      *r = (*ps <<ishift) & BITMASK;
+	      if ((++ps) < VARBITEND(arg))
+		*r |= *ps >>(BITSPERBYTE-ishift);
+	      r++;
+	    }
+	}
+      /* Do we need to pad at the end? */
+      ipad = VARBITPAD(result);
+      if (ipad > 0) 
+	{
+	  mask = BITMASK << ipad;
+	  *(VARBITS(result) + len - 1) &= mask;
+	}
+    }
+
+  return result;
+}
+
+/* bitand
+ * perform a logical AND on two bit strings. The result is automatically
+ * truncated to the shorter bit string
+ */
+char *
+bitand (char * arg1, char * arg2)
+{
+  int len,
+    i;
+  char *result;
+  bits8 *p1, 
+    *p2, 
+    *r;
+
+  if (!PointerIsValid(arg1) || !PointerIsValid(arg2))
+    return (bool) 0;
+
+  len = Min(VARSIZE(arg1),VARSIZE(arg2));
+  result = (char *) palloc(len);
+  VARSIZE(result) = len;
+  VARBITLEN(result) = Min(VARBITLEN(arg1),VARBITLEN(arg2));
+
+  p1 = (bits8 *) VARBITS(arg1);
+  p2 = (bits8 *) VARBITS(arg2);
+  r = (bits8 *) VARBITS(result);
+  for (i=0; i<Min(VARBITBYTES(arg1),VARBITBYTES(arg2)); i++)
+    *r++ = *p1++ & *p2++;
+  
+  /* Padding is not needed as & of 0 pad is 0 */
+  
+  return result;
+}
+
+/* bitor
+ * perform a logical OR on two bit strings. The result is automatically
+ * truncated to the shorter bit string.
+ */
+char *
+bitor (char * arg1, char * arg2)
+{
+  int len,
+    i;
+  char *result;
+  bits8 *p1, 
+    *p2, 
+    *r;
+  bits8 mask;
+
+  if (!PointerIsValid(arg1) || !PointerIsValid(arg2))
+    return (bool) 0;
+
+  len = Min(VARSIZE(arg1),VARSIZE(arg2));
+  result = (char *) palloc(len);
+  VARSIZE(result) = len;
+  VARBITLEN(result) = Min(VARBITLEN(arg1),VARBITLEN(arg2));
+
+  p1 = (bits8 *) VARBITS(arg1);
+  p2 = (bits8 *) VARBITS(arg2);
+  r = (bits8 *) VARBITS(result);
+  for (i=0; i<Min(VARBITBYTES(arg1),VARBITBYTES(arg2)); i++)
+    *r++ = *p1++ | *p2++;
+
+  /* Pad the result */
+  mask = BITMASK << VARBITPAD(result);
+  *r &= mask;
+  
+  return result;
+}
+
+/* bitxor
+ * perform a logical XOR on two bit strings. The result is automatically
+ * truncated to the shorter bit string.
+ */
+char *
+bitxor (char * arg1, char * arg2)
+{
+  int len,
+    i;
+  char *result;
+  bits8 *p1, 
+    *p2, 
+    *r;
+  bits8 mask;
+
+  if (!PointerIsValid(arg1) || !PointerIsValid(arg2))
+    return (bool) 0;
+
+  len = Min(VARSIZE(arg1),VARSIZE(arg2));
+  result = (char *) palloc(len);
+  VARSIZE(result) = len;
+  VARBITLEN(result) = Min(VARBITLEN(arg1),VARBITLEN(arg2));
+
+  p1 = (bits8 *) VARBITS(arg1);
+  p2 = (bits8 *) VARBITS(arg2);
+  r = (bits8 *) VARBITS(result);
+  for (i=0; i<Min(VARBITBYTES(arg1),VARBITBYTES(arg2)); i++)
+    {
+      *r++ = *p1++ ^ *p2++;
+    }
+
+  /* Pad the result */
+  mask = BITMASK << VARBITPAD(result);
+  *r &= mask;
+  
+  return result;
+}
+
+/* bitnot
+ * perform a logical NOT on a bit strings.
+ */
+char *
+bitnot (char * arg)
+{
+  int len;
+  char *result;
+  bits8 *p, 
+    *r;
+  bits8 mask;
+
+  if (!PointerIsValid(arg))
+    return (bool) 0;
+
+  result = (char *) palloc(VARSIZE(arg));
+  VARSIZE(result) = VARSIZE(arg);
+  VARBITLEN(result) = VARBITLEN(arg);
+
+  p = (bits8 *) VARBITS(arg);
+  r = (bits8 *) VARBITS(result);
+  for ( ; p < VARBITEND(arg); p++, r++)
+    *r = ~*p;
+
+  /* Pad the result */
+  mask = BITMASK << VARBITPAD(result);
+  *r &= mask;
+  
+  return result;
+}
+
+/* bitshiftleft
+ * do a left shift (i.e. to the beginning of the string) of the bit string
+ */
+char *
+bitshiftleft (char * arg, int shft)
+{
+  int byte_shift, ishift, len;
+  char *result;
+  bits8 *p, 
+    *r;
+
+  if (!PointerIsValid(arg))
+    return (bool) 0;
+
+  /* Negative shift is a shift to the right */
+  if (shft < 0) 
+    return bitshiftright(arg, -shft);
+
+  result = (char *) palloc(VARSIZE(arg));
+  VARSIZE(result) = VARSIZE(arg);
+  VARBITLEN(result) = VARBITLEN(arg);
+  r = (bits8 *) VARBITS(result);
+
+  byte_shift = shft/BITSPERBYTE;
+  ishift = shft % BITSPERBYTE;
+  p = ((bits8 *) VARBITS(arg)) + byte_shift;
+  
+  if (ishift == 0) {
+    /* Special case: we can do a memcpy */
+    len = VARBITBYTES(arg) - byte_shift;
+    memcpy(r, p, len);
+    memset(r+len, 0, byte_shift);
+  } else {
+    for ( ; p < VARBITEND(arg); r++) {
+      *r = *p <<ishift;
+      if ((++p) < VARBITEND(arg))
+	*r |= *p >>(BITSPERBYTE-ishift);
+    }
+    for ( ; r < VARBITEND(result) ; r++ ) 
+      *r = (bits8) 0;
+  }
+
+  return result;
+}
+
+/* bitshiftright
+ * do a right shift (i.e. to the beginning of the string) of the bit string
+ */
+char *
+bitshiftright (char * arg, int shft)
+{
+  int byte_shift, ishift, len;
+  char *result;
+  bits8 *p, 
+    *r;
+
+  if (!PointerIsValid(arg))
+    return (bool) 0;
+
+  /* Negative shift is a shift to the left */
+  if (shft < 0) 
+    return bitshiftleft(arg, -shft);
+
+  result = (char *) palloc(VARSIZE(arg));
+  VARSIZE(result) = VARSIZE(arg);
+  VARBITLEN(result) = VARBITLEN(arg);
+  r = (bits8 *) VARBITS(result);
+
+  byte_shift = shft/BITSPERBYTE;
+  ishift = shft % BITSPERBYTE;
+  p = (bits8 *) VARBITS(arg);
+
+  /* Set the first part of the result to 0 */
+  memset(r, 0, byte_shift);
+  
+  if (ishift == 0) 
+    {
+      /* Special case: we can do a memcpy */
+      len = VARBITBYTES(arg) - byte_shift;
+      memcpy(r+byte_shift, p, len);
+    } 
+  else 
+    {
+      r += byte_shift;
+      *r = 0;    /* Initialise first byte */
+      for ( ; r < VARBITEND(result); p++) {
+	*r |= *p >> ishift;
+	if ((++r) < VARBITEND(result))
+	  *r = (*p <<(BITSPERBYTE-ishift)) & BITMASK;
+      }
+    }
+
+  return result;
+}