Fix integer-to-bit-string conversions to handle the first fractional byte

correctly when the output bit width is wider than the given integer by
something other than a multiple of 8 bits.

This has been wrong since I first wrote that code for 8.0 :-(.  Kudos to
Roman Kononov for being the first to notice, though I didn't use his
patch.  Per bug #5237.

diff --git a/src/backend/utils/adt/varbit.c b/src/backend/utils/adt/varbit.c
index 389749961c699f37effe787b60bfca9e99af0c45..e027a017dcc85abd18bed9053b9e98f02a5b32cd 100644 (file)
--- a/src/backend/utils/adt/varbit.c
+++ b/src/backend/utils/adt/varbit.c
@@ -9,7 +9,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/utils/adt/varbit.c,v 1.47.2.1 2007/08/21 02:40:18 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/utils/adt/varbit.c,v 1.47.2.2 2009/12/12 19:25:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1265,7 +1265,12 @@ bitfromint4(PG_FUNCTION_ARGS)
    /* store first fractional byte */
    if (destbitsleft > srcbitsleft)
    {
-       *r++ = (bits8) ((a >> (srcbitsleft - 8)) & BITMASK);
+       int     val = (int) (a >> (destbitsleft - 8));
+
+       /* Force sign-fill in case the compiler implements >> as zero-fill */
+       if (a < 0)
+           val |= (-1) << (srcbitsleft + 8 - destbitsleft);
+       *r++ = (bits8) (val & BITMASK);
        destbitsleft -= 8;
    }
    /* Now srcbitsleft and destbitsleft are the same, need not track both */
@@ -1344,7 +1349,12 @@ bitfromint8(PG_FUNCTION_ARGS)
    /* store first fractional byte */
    if (destbitsleft > srcbitsleft)
    {
-       *r++ = (bits8) ((a >> (srcbitsleft - 8)) & BITMASK);
+       int     val = (int) (a >> (destbitsleft - 8));
+
+       /* Force sign-fill in case the compiler implements >> as zero-fill */
+       if (a < 0)
+           val |= (-1) << (srcbitsleft + 8 - destbitsleft);
+       *r++ = (bits8) (val & BITMASK);
        destbitsleft -= 8;
    }
    /* Now srcbitsleft and destbitsleft are the same, need not track both */