| Message ID | 1337520203-29147-1-git-send-email-akinobu.mita@gmail.com |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Sun 20-05-12 22:23:14, Akinobu Mita wrote: > memweight() is the function that counts the total number of bits set > in memory area. The memory area doesn't need to be aligned to > long-word boundary unlike bitmap_weight(). Thanks for the patch. I have some comments below. > Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> > Cc: Anders Larsen <al@alarsen.net> > Cc: Alasdair Kergon <agk@redhat.com> > Cc: dm-devel@redhat.com > Cc: linux-fsdevel@vger.kernel.org > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com> > Cc: linux-media@vger.kernel.org > Cc: Mark Fasheh <mfasheh@suse.com> > Cc: Joel Becker <jlbec@evilplan.org> > Cc: ocfs2-devel@oss.oracle.com > Cc: Jan Kara <jack@suse.cz> > Cc: linux-ext4@vger.kernel.org > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Andreas Dilger <adilger.kernel@dilger.ca> > Cc: "Theodore Ts'o" <tytso@mit.edu> > --- > include/linux/string.h | 3 +++ > lib/string.c | 37 +++++++++++++++++++++++++++++++++++++ > 2 files changed, 40 insertions(+), 0 deletions(-) > > diff --git a/include/linux/string.h b/include/linux/string.h > index e033564..ffe0442 100644 > --- a/include/linux/string.h > +++ b/include/linux/string.h > @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix) > return strncmp(str, prefix, strlen(prefix)) == 0; > } > #endif > + > +extern size_t memweight(const void *ptr, size_t bytes); > + > #endif /* _LINUX_STRING_H_ */ > diff --git a/lib/string.c b/lib/string.c > index e5878de..c8b92a0 100644 > --- a/lib/string.c > +++ b/lib/string.c > @@ -26,6 +26,7 @@ > #include <linux/export.h> > #include <linux/bug.h> > #include <linux/errno.h> > +#include <linux/bitmap.h> > > #ifndef __HAVE_ARCH_STRNICMP > /** > @@ -824,3 +825,39 @@ void *memchr_inv(const void *start, int c, size_t bytes) > return check_bytes8(start, value, bytes % 8); > } > EXPORT_SYMBOL(memchr_inv); > + > +/** > + * memweight - count the total number of bits set in memory area > + * @ptr: pointer to the start of the area > + * @bytes: the size of the area > + */ > +size_t memweight(const void *ptr, size_t bytes) > +{ > + size_t w = 0; > + size_t longs; > + union { > + const void *ptr; > + const unsigned char *b; > + unsigned long address; > + } bitmap; Ugh, this is ugly and mostly unnecessary. Just use "const unsigned char *bitmap". > + > + for (bitmap.ptr = ptr; bytes > 0 && bitmap.address % sizeof(long); > + bytes--, bitmap.address++) > + w += hweight8(*bitmap.b); This can be: count = ((unsigned long)bitmap) % sizeof(long); while (count--) { w += hweight(*bitmap); bitmap++; bytes--; } > + > + for (longs = bytes / sizeof(long); longs > 0; ) { > + size_t bits = min_t(size_t, INT_MAX & ~(BITS_PER_LONG - 1), > + longs * BITS_PER_LONG); I find it highly unlikely that someone would have such a large bitmap (256 MB or more on 32-bit). Also the condition as you wrote it can just overflow so it won't have the desired effect. Just do BUG_ON(longs >= ULONG_MAX / BITS_PER_LONG); and remove the loop completely. If someone comes with such a huge bitmap, the code can be modified easily (after really closely inspecting whether such a huge bitmap is really well justified). > + > + w += bitmap_weight(bitmap.ptr, bits); > + bytes -= bits / BITS_PER_BYTE; > + bitmap.address += bits / BITS_PER_BYTE; > + longs -= bits / BITS_PER_LONG; > + } > + > + for (; bytes > 0; bytes--, bitmap.address++) > + w += hweight8(*bitmap.b); > + > + return w; > +} > +EXPORT_SYMBOL(memweight); Honza
2012/5/23 Jan Kara <jack@suse.cz>: > On Sun 20-05-12 22:23:14, Akinobu Mita wrote: >> memweight() is the function that counts the total number of bits set >> in memory area. The memory area doesn't need to be aligned to >> long-word boundary unlike bitmap_weight(). > Thanks for the patch. I have some comments below. Thanks for the review. >> @@ -824,3 +825,39 @@ void *memchr_inv(const void *start, int c, size_t bytes) >> return check_bytes8(start, value, bytes % 8); >> } >> EXPORT_SYMBOL(memchr_inv); >> + >> +/** >> + * memweight - count the total number of bits set in memory area >> + * @ptr: pointer to the start of the area >> + * @bytes: the size of the area >> + */ >> +size_t memweight(const void *ptr, size_t bytes) >> +{ >> + size_t w = 0; >> + size_t longs; >> + union { >> + const void *ptr; >> + const unsigned char *b; >> + unsigned long address; >> + } bitmap; > Ugh, this is ugly and mostly unnecessary. Just use "const unsigned char > *bitmap". > >> + >> + for (bitmap.ptr = ptr; bytes > 0 && bitmap.address % sizeof(long); >> + bytes--, bitmap.address++) >> + w += hweight8(*bitmap.b); > This can be: > count = ((unsigned long)bitmap) % sizeof(long); The count should be the size of unaligned area and it can be greater than bytes. So count = min(bytes, sizeof(long) - ((unsigned long)bitmap) % sizeof(long)); > while (count--) { > w += hweight(*bitmap); > bitmap++; > bytes--; > } >> + >> + for (longs = bytes / sizeof(long); longs > 0; ) { >> + size_t bits = min_t(size_t, INT_MAX & ~(BITS_PER_LONG - 1), >> + longs * BITS_PER_LONG); > I find it highly unlikely that someone would have such a large bitmap > (256 MB or more on 32-bit). Also the condition as you wrote it can just > overflow so it won't have the desired effect. Just do > BUG_ON(longs >= ULONG_MAX / BITS_PER_LONG); The bits argument of bitmap_weight() is int type. So this should be BUG_ON(longs >= INT_MAX / BITS_PER_LONG); > and remove the loop completely. If someone comes with such a huge bitmap, > the code can be modified easily (after really closely inspecting whether > such a huge bitmap is really well justified). size_t memweight(const void *ptr, size_t bytes) { size_t w = 0; size_t longs; const unsigned char *bitmap = ptr; for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long); bytes--, bitmap++) w += hweight8(*bitmap); longs = bytes / sizeof(long); BUG_ON(longs >= INT_MAX / BITS_PER_LONG); w += bitmap_weight((unsigned long *)bitmap, longs * BITS_PER_LONG); bytes -= longs * sizeof(long); bitmap += longs * sizeof(long); for (; bytes > 0; bytes--, bitmap++) w += hweight8(*bitmap); return w; } -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed 23-05-12 21:12:18, Akinobu Mita wrote: > 2012/5/23 Jan Kara <jack@suse.cz>: > > On Sun 20-05-12 22:23:14, Akinobu Mita wrote: > >> memweight() is the function that counts the total number of bits set > >> in memory area. The memory area doesn't need to be aligned to > >> long-word boundary unlike bitmap_weight(). > > Thanks for the patch. I have some comments below. > > Thanks for the review. > > >> @@ -824,3 +825,39 @@ void *memchr_inv(const void *start, int c, size_t bytes) > >> return check_bytes8(start, value, bytes % 8); > >> } > >> EXPORT_SYMBOL(memchr_inv); > >> + > >> +/** > >> + * memweight - count the total number of bits set in memory area > >> + * @ptr: pointer to the start of the area > >> + * @bytes: the size of the area > >> + */ > >> +size_t memweight(const void *ptr, size_t bytes) > >> +{ > >> + size_t w = 0; > >> + size_t longs; > >> + union { > >> + const void *ptr; > >> + const unsigned char *b; > >> + unsigned long address; > >> + } bitmap; > > Ugh, this is ugly and mostly unnecessary. Just use "const unsigned char > > *bitmap". > > > >> + > >> + for (bitmap.ptr = ptr; bytes > 0 && bitmap.address % sizeof(long); > >> + bytes--, bitmap.address++) > >> + w += hweight8(*bitmap.b); > > This can be: > > count = ((unsigned long)bitmap) % sizeof(long); > > The count should be the size of unaligned area and it can be greater than > bytes. So > > count = min(bytes, > sizeof(long) - ((unsigned long)bitmap) % sizeof(long)); You are right, I didn't quite think this through. > > while (count--) { > > w += hweight(*bitmap); > > bitmap++; > > bytes--; > > } > >> + > >> + for (longs = bytes / sizeof(long); longs > 0; ) { > >> + size_t bits = min_t(size_t, INT_MAX & ~(BITS_PER_LONG - 1), > >> + longs * BITS_PER_LONG); > > I find it highly unlikely that someone would have such a large bitmap > > (256 MB or more on 32-bit). Also the condition as you wrote it can just > > overflow so it won't have the desired effect. Just do > > BUG_ON(longs >= ULONG_MAX / BITS_PER_LONG); > > The bits argument of bitmap_weight() is int type. So this should be > > BUG_ON(longs >= INT_MAX / BITS_PER_LONG); OK, I didn't check and thought it's size_t. > > and remove the loop completely. If someone comes with such a huge bitmap, > > the code can be modified easily (after really closely inspecting whether > > such a huge bitmap is really well justified). > > size_t memweight(const void *ptr, size_t bytes) > { > size_t w = 0; > size_t longs; > const unsigned char *bitmap = ptr; > > for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long); > bytes--, bitmap++) > w += hweight8(*bitmap); > > longs = bytes / sizeof(long); > BUG_ON(longs >= INT_MAX / BITS_PER_LONG); > w += bitmap_weight((unsigned long *)bitmap, longs * BITS_PER_LONG); > bytes -= longs * sizeof(long); > bitmap += longs * sizeof(long); > > for (; bytes > 0; bytes--, bitmap++) > w += hweight8(*bitmap); > > return w; > } Yup, this looks much more readable. Thanks! Honza
On Wed, May 23, 2012 at 09:12:18PM +0900, Akinobu Mita wrote: > size_t memweight(const void *ptr, size_t bytes) Why should this return size_t instead of unsigned long? > { > size_t w = 0; > size_t longs; > const unsigned char *bitmap = ptr; > > for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long); > bytes--, bitmap++) > w += hweight8(*bitmap); > > longs = bytes / sizeof(long); > BUG_ON(longs >= INT_MAX / BITS_PER_LONG); > w += bitmap_weight((unsigned long *)bitmap, longs * BITS_PER_LONG); > bytes -= longs * sizeof(long); > bitmap += longs * sizeof(long); > > for (; bytes > 0; bytes--, bitmap++) > w += hweight8(*bitmap); > > return w; > } bitmap_weight copes with a bitmask that isn't a multiple of BITS_PER_LONG in size already. So I think this can be done as: unsigned long memweight(const void *s, size_t n) { const unsigned char *ptr = s; unsigned long r = 0; while (n > 0 && (unsigned long)ptr % sizeof(long)) { r += hweight8(*ptr); n--; ptr++; } BUG_ON(n >= INT_MAX / 8) return r + bitmap_weight((unsigned long *)ptr, n * 8); }
2012/5/23 Matthew Wilcox <matthew@wil.cx>: > On Wed, May 23, 2012 at 09:12:18PM +0900, Akinobu Mita wrote: >> size_t memweight(const void *ptr, size_t bytes) > > Why should this return size_t instead of unsigned long? I just use the same type as the bytes argument without mature consideration. If unsigned long is better than size_t, I'll change the return type. >> { >> size_t w = 0; >> size_t longs; >> const unsigned char *bitmap = ptr; >> >> for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long); >> bytes--, bitmap++) >> w += hweight8(*bitmap); >> >> longs = bytes / sizeof(long); >> BUG_ON(longs >= INT_MAX / BITS_PER_LONG); >> w += bitmap_weight((unsigned long *)bitmap, longs * BITS_PER_LONG); >> bytes -= longs * sizeof(long); >> bitmap += longs * sizeof(long); >> >> for (; bytes > 0; bytes--, bitmap++) >> w += hweight8(*bitmap); >> >> return w; >> } > > bitmap_weight copes with a bitmask that isn't a multiple of BITS_PER_LONG > in size already. So I think this can be done as: > > unsigned long memweight(const void *s, size_t n) > { > const unsigned char *ptr = s; > unsigned long r = 0; > > while (n > 0 && (unsigned long)ptr % sizeof(long)) { > r += hweight8(*ptr); > n--; > ptr++; > } > > BUG_ON(n >= INT_MAX / 8) > > return r + bitmap_weight((unsigned long *)ptr, n * 8); > } This works perfectly on little-endian machines. But it doesn't work on big-endian machines, if the bottom edge of memory area is not aligned on long word boundary. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/string.h b/include/linux/string.h index e033564..ffe0442 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix) return strncmp(str, prefix, strlen(prefix)) == 0; } #endif + +extern size_t memweight(const void *ptr, size_t bytes); + #endif /* _LINUX_STRING_H_ */ diff --git a/lib/string.c b/lib/string.c index e5878de..c8b92a0 100644 --- a/lib/string.c +++ b/lib/string.c @@ -26,6 +26,7 @@ #include <linux/export.h> #include <linux/bug.h> #include <linux/errno.h> +#include <linux/bitmap.h> #ifndef __HAVE_ARCH_STRNICMP /** @@ -824,3 +825,39 @@ void *memchr_inv(const void *start, int c, size_t bytes) return check_bytes8(start, value, bytes % 8); } EXPORT_SYMBOL(memchr_inv); + +/** + * memweight - count the total number of bits set in memory area + * @ptr: pointer to the start of the area + * @bytes: the size of the area + */ +size_t memweight(const void *ptr, size_t bytes) +{ + size_t w = 0; + size_t longs; + union { + const void *ptr; + const unsigned char *b; + unsigned long address; + } bitmap; + + for (bitmap.ptr = ptr; bytes > 0 && bitmap.address % sizeof(long); + bytes--, bitmap.address++) + w += hweight8(*bitmap.b); + + for (longs = bytes / sizeof(long); longs > 0; ) { + size_t bits = min_t(size_t, INT_MAX & ~(BITS_PER_LONG - 1), + longs * BITS_PER_LONG); + + w += bitmap_weight(bitmap.ptr, bits); + bytes -= bits / BITS_PER_BYTE; + bitmap.address += bits / BITS_PER_BYTE; + longs -= bits / BITS_PER_LONG; + } + + for (; bytes > 0; bytes--, bitmap.address++) + w += hweight8(*bitmap.b); + + return w; +} +EXPORT_SYMBOL(memweight);
memweight() is the function that counts the total number of bits set in memory area. The memory area doesn't need to be aligned to long-word boundary unlike bitmap_weight(). Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Cc: Anders Larsen <al@alarsen.net> Cc: Alasdair Kergon <agk@redhat.com> Cc: dm-devel@redhat.com Cc: linux-fsdevel@vger.kernel.org Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Cc: linux-media@vger.kernel.org Cc: Mark Fasheh <mfasheh@suse.com> Cc: Joel Becker <jlbec@evilplan.org> Cc: ocfs2-devel@oss.oracle.com Cc: Jan Kara <jack@suse.cz> Cc: linux-ext4@vger.kernel.org Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andreas Dilger <adilger.kernel@dilger.ca> Cc: "Theodore Ts'o" <tytso@mit.edu> --- include/linux/string.h | 3 +++ lib/string.c | 37 +++++++++++++++++++++++++++++++++++++ 2 files changed, 40 insertions(+), 0 deletions(-)