Message ID | 20231026135912.1214302-1-glider@google.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [v10,1/2] lib/bitmap: add bitmap_{read,write}() | expand |
On Thu, Oct 26, 2023 at 03:59:11PM +0200, Alexander Potapenko wrote: > From: Syed Nayyar Waris <syednwaris@gmail.com> > > The two new functions allow reading/writing values of length up to > BITS_PER_LONG bits at arbitrary position in the bitmap. > > The code was taken from "bitops: Introduce the for_each_set_clump macro" > by Syed Nayyar Waris with a number of changes and simplifications: > - instead of using roundup(), which adds an unnecessary dependency > on <linux/math.h>, we calculate space as BITS_PER_LONG-offset; > - indentation is reduced by not using else-clauses (suggested by > checkpatch for bitmap_get_value()); > - bitmap_get_value()/bitmap_set_value() are renamed to bitmap_read() > and bitmap_write(); > - some redundant computations are omitted. Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> One nit below, though. ... > +/** > + * bitmap_write - write n-bit value within a memory region > + * @map: address to the bitmap memory region > + * @value: value to write, clamped to nbits > + * @start: bit offset of the n-bit value > + * @nbits: size of value in bits, nonzero, up to BITS_PER_LONG. > + * > + * bitmap_write() behaves as-if implemented as @nbits calls of __assign_bit(), > + * i.e. bits beyond @nbits are ignored: > + * > + * for (bit = 0; bit < nbits; bit++) > + * __assign_bit(start + bit, bitmap, val & BIT(bit)); > + * > + * For @nbits > BITS_PER_LONG no writes are performed. nbits == 0 hasn't been mentioned. (no, the main nit below) > + */ > +static inline void bitmap_write(unsigned long *map, > + unsigned long value, > + unsigned long start, unsigned long nbits) While noticing strange indentation (you have space for the parameter on the previous line, I realized that this is a counter-intuitive interface. Can you actually make value the last parameter?
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Thanks! > One nit below, though. > > ... > > > +/** > > + * bitmap_write - write n-bit value within a memory region > > + * @map: address to the bitmap memory region > > + * @value: value to write, clamped to nbits > > + * @start: bit offset of the n-bit value > > + * @nbits: size of value in bits, nonzero, up to BITS_PER_LONG. > > + * > > + * bitmap_write() behaves as-if implemented as @nbits calls of __assign_bit(), > > + * i.e. bits beyond @nbits are ignored: > > + * > > + * for (bit = 0; bit < nbits; bit++) > > + * __assign_bit(start + bit, bitmap, val & BIT(bit)); > > + * > > + * For @nbits > BITS_PER_LONG no writes are performed. > > nbits == 0 hasn't been mentioned. I can mention it explicitly, but it is already covered by the for-loop above: if nbits==0, no bits are assigned. > > (no, the main nit below) > > > + */ > > +static inline void bitmap_write(unsigned long *map, > > + unsigned long value, > > + unsigned long start, unsigned long nbits) > > While noticing strange indentation (you have space for the parameter on > the previous line, I believe I do not, maybe that's something on your side? There are tabs in the source, and in the original email. > I realized that this is a counter-intuitive interface. > Can you actually make value the last parameter? It is consistent with bitmap_set_value8(map, value, start), and in all the functions above @nbits is the last parameter.
On Thu, Oct 26, 2023 at 04:48:46PM +0200, Alexander Potapenko wrote: ... > > > +static inline void bitmap_write(unsigned long *map, > > > + unsigned long value, > > > + unsigned long start, unsigned long nbits) > > > > While noticing strange indentation (you have space for the parameter on > > the previous line, > > I believe I do not, maybe that's something on your side? > There are tabs in the source, and in the original email. I meant that you can use 2 lines instead of 3: static inline void bitmap_write(unsigned long *map, unsigned long value, unsigned long start, unsigned long nbits) > > I realized that this is a counter-intuitive interface. > > Can you actually make value the last parameter? > > It is consistent with bitmap_set_value8(map, value, start), and in all > the functions above @nbits is the last parameter. Oh, then I leave this to Yury.
On Thu, Oct 26, 2023 at 10:14 PM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > On Thu, Oct 26, 2023 at 04:48:46PM +0200, Alexander Potapenko wrote: > > ... > > > > > +static inline void bitmap_write(unsigned long *map, > > > > + unsigned long value, > > > > + unsigned long start, unsigned long nbits) > > > > > > While noticing strange indentation (you have space for the parameter on > > > the previous line, > > > > I believe I do not, maybe that's something on your side? > > There are tabs in the source, and in the original email. > > I meant that you can use 2 lines instead of 3: > > static inline void bitmap_write(unsigned long *map, unsigned long value, > unsigned long start, unsigned long nbits) > > > > I realized that this is a counter-intuitive interface. > > > Can you actually make value the last parameter? > > > > It is consistent with bitmap_set_value8(map, value, start), and in all > > the functions above @nbits is the last parameter. Oh, I see. Let me fix that.
On Thu, Oct 26, 2023 at 10:14 PM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > On Thu, Oct 26, 2023 at 04:48:46PM +0200, Alexander Potapenko wrote: > > ... > > > > > +static inline void bitmap_write(unsigned long *map, > > > > + unsigned long value, > > > > + unsigned long start, unsigned long nbits) > > > > > > While noticing strange indentation (you have space for the parameter on > > > the previous line, > > > > I believe I do not, maybe that's something on your side? > > There are tabs in the source, and in the original email. > > I meant that you can use 2 lines instead of 3: > > static inline void bitmap_write(unsigned long *map, unsigned long value, > unsigned long start, unsigned long nbits) > Sorry, my previous reply was incorrectly attributed. I will fix bitmap_write.
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index 03644237e1efb..f5745b505a194 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -77,6 +77,10 @@ struct device; * bitmap_to_arr64(buf, src, nbits) Copy nbits from buf to u64[] dst * bitmap_get_value8(map, start) Get 8bit value from map at start * bitmap_set_value8(map, value, start) Set 8bit value to map at start + * bitmap_read(map, start, nbits) Read an nbits-sized value from + * map at start + * bitmap_write(map, value, start, nbits) Write an nbits-sized value to + * map at start * * Note, bitmap_zero() and bitmap_fill() operate over the region of * unsigned longs, that is, bits behind bitmap till the unsigned long @@ -599,6 +603,80 @@ static inline void bitmap_set_value8(unsigned long *map, unsigned long value, map[index] |= value << offset; } +/** + * bitmap_read - read a value of n-bits from the memory region + * @map: address to the bitmap memory region + * @start: bit offset of the n-bit value + * @nbits: size of value in bits, nonzero, up to BITS_PER_LONG + * + * Returns: value of @nbits bits located at the @start bit offset within the + * @map memory region. For @nbits = 0 and @nbits > BITS_PER_LONG the return + * value is undefined. + */ +static inline unsigned long bitmap_read(const unsigned long *map, + unsigned long start, + unsigned long nbits) +{ + size_t index = BIT_WORD(start); + unsigned long offset = start % BITS_PER_LONG; + unsigned long space = BITS_PER_LONG - offset; + unsigned long value_low, value_high; + + if (unlikely(!nbits || nbits > BITS_PER_LONG)) + return 0; + + if (space >= nbits) + return (map[index] >> offset) & BITMAP_LAST_WORD_MASK(nbits); + + value_low = map[index] & BITMAP_FIRST_WORD_MASK(start); + value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits); + return (value_low >> offset) | (value_high << space); +} + +/** + * bitmap_write - write n-bit value within a memory region + * @map: address to the bitmap memory region + * @value: value to write, clamped to nbits + * @start: bit offset of the n-bit value + * @nbits: size of value in bits, nonzero, up to BITS_PER_LONG. + * + * bitmap_write() behaves as-if implemented as @nbits calls of __assign_bit(), + * i.e. bits beyond @nbits are ignored: + * + * for (bit = 0; bit < nbits; bit++) + * __assign_bit(start + bit, bitmap, val & BIT(bit)); + * + * For @nbits > BITS_PER_LONG no writes are performed. + */ +static inline void bitmap_write(unsigned long *map, + unsigned long value, + unsigned long start, unsigned long nbits) +{ + size_t index; + unsigned long offset; + unsigned long space; + unsigned long mask; + bool fit; + + if (unlikely(!nbits || nbits > BITS_PER_LONG)) + return; + + mask = BITMAP_LAST_WORD_MASK(nbits); + value &= mask; + offset = start % BITS_PER_LONG; + space = BITS_PER_LONG - offset; + fit = space >= nbits; + index = BIT_WORD(start); + + map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start)); + map[index] |= value << offset; + if (fit) + return; + + map[index + 1] &= BITMAP_FIRST_WORD_MASK(start + nbits); + map[index + 1] |= (value >> space); +} + #endif /* __ASSEMBLY__ */ #endif /* __LINUX_BITMAP_H */