Date: Sat, 7 Oct 2000 21:35:40 +0100 From: David Malone <dwmalone@maths.tcd.ie> To: dwmalone@FreeBSD.org Cc: freebsd-bugs@FreeBSD.org, bob@immure.com, bde@FreeBSD.org Subject: Re: misc/21204: bit_ffc and bit_ffs macros in bitstring.h test 1 byte too many. Message-ID: <20001007213540.A15000@walton.maths.tcd.ie> In-Reply-To: <20001006134808.A87828@walton.maths.tcd.ie>; from dwmalone@maths.tcd.ie on Fri, Oct 06, 2000 at 01:48:08PM %2B0100 References: <200010022119.OAA17662@freefall.freebsd.org> <20001005105720.A1562@turing.maths.tcd.ie> <20001006134808.A87828@walton.maths.tcd.ie>
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I intend to commit the following patch to bitstring.h. It does the
following:
1) fixes the problems with bit_ffs and bit_ffc searching
off the end of the bitstring,
2) Makes our version of bitstring.h much more like NetBSD's,
adding extra brackets and do { ... } while(0);,
3) Change bitstr_size and bit_alloc to match NetBSD's
(same results, neater macros).
NetBSD has a different fix for the bitstring problems which produce
much slower code according to Bob Wilcox's tests.
David.
Index: bitstring.h
===================================================================
RCS file: /cvs/FreeBSD-CVS/src/include/bitstring.h,v
retrieving revision 1.1.1.1
diff -u -r1.1.1.1 bitstring.h
--- bitstring.h 1994/05/24 09:57:25 1.1.1.1
+++ bitstring.h 2000/10/07 19:38:17
@@ -53,16 +53,15 @@
/* external macros */
/* bytes in a bitstring of nbits bits */
#define bitstr_size(nbits) \
- ((((nbits) - 1) >> 3) + 1)
+ (((nbits) + 7) >> 3)
/* allocate a bitstring */
#define bit_alloc(nbits) \
- (bitstr_t *)calloc(1, \
- (unsigned int)bitstr_size(nbits) * sizeof(bitstr_t))
+ (bitstr_t *)calloc((size_t)bitstr_size(nbits), sizeof(bitstr_t))
/* allocate a bitstring on the stack */
#define bit_decl(name, nbits) \
- (name)[bitstr_size(nbits)]
+ ((name)[bitstr_size(nbits)])
/* is bit N of bitstring name set? */
#define bit_test(name, bit) \
@@ -70,14 +69,14 @@
/* set bit N of bitstring name */
#define bit_set(name, bit) \
- (name)[_bit_byte(bit)] |= _bit_mask(bit)
+ ((name)[_bit_byte(bit)] |= _bit_mask(bit))
/* clear bit N of bitstring name */
#define bit_clear(name, bit) \
- (name)[_bit_byte(bit)] &= ~_bit_mask(bit)
+ ((name)[_bit_byte(bit)] &= ~_bit_mask(bit))
/* clear bits start ... stop in bitstring */
-#define bit_nclear(name, start, stop) { \
+#define bit_nclear(name, start, stop) do { \
register bitstr_t *_name = name; \
register int _start = start, _stop = stop; \
register int _startbyte = _bit_byte(_start); \
@@ -91,10 +90,10 @@
_name[_startbyte] = 0; \
_name[_stopbyte] &= 0xff << ((_stop&0x7) + 1); \
} \
-}
+} while (0)
/* set bits start ... stop in bitstring */
-#define bit_nset(name, start, stop) { \
+#define bit_nset(name, start, stop) do { \
register bitstr_t *_name = name; \
register int _start = start, _stop = stop; \
register int _startbyte = _bit_byte(_start); \
@@ -108,13 +107,13 @@
_name[_startbyte] = 0xff; \
_name[_stopbyte] |= 0xff >> (7 - (_stop&0x7)); \
} \
-}
+} while (0)
/* find first bit clear in name */
-#define bit_ffc(name, nbits, value) { \
+#define bit_ffc(name, nbits, value) do { \
register bitstr_t *_name = name; \
register int _byte, _nbits = nbits; \
- register int _stopbyte = _bit_byte(_nbits), _value = -1; \
+ register int _stopbyte = _bit_byte(_nbits-1), _value = -1; \
for (_byte = 0; _byte <= _stopbyte; ++_byte) \
if (_name[_byte] != 0xff) { \
_value = _byte << 3; \
@@ -122,14 +121,16 @@
++_value, _stopbyte >>= 1); \
break; \
} \
+ if (_value >= nbits) \
+ _value = -1; \
*(value) = _value; \
-}
+} while (0)
/* find first bit set in name */
-#define bit_ffs(name, nbits, value) { \
+#define bit_ffs(name, nbits, value) do { \
register bitstr_t *_name = name; \
register int _byte, _nbits = nbits; \
- register int _stopbyte = _bit_byte(_nbits), _value = -1; \
+ register int _stopbyte = _bit_byte(_nbits - 1), _value = -1; \
for (_byte = 0; _byte <= _stopbyte; ++_byte) \
if (_name[_byte]) { \
_value = _byte << 3; \
@@ -137,7 +138,9 @@
++_value, _stopbyte >>= 1); \
break; \
} \
+ if (_value >= nbits) \
+ _value = -1; \
*(value) = _value; \
-}
+} while (0)
#endif /* !_BITSTRING_H_ */
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