bitmap: Introduce bitmap_cut(): cut bits and shift remaining (20927671) · Commits · 戴 / test

include/linux/bitmap.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -53,6 +53,7 @@
		* bitmap_find_next_zero_area_off(buf, len, pos, n, mask) as above
		* bitmap_shift_right(dst, src, n, nbits) dst = src >> n
		* bitmap_shift_left(dst, src, n, nbits) dst = src << n
		* bitmap_cut(dst, src, first, n, nbits) Cut n bits from first, copy rest
		* bitmap_replace(dst, old, new, mask, nbits) dst = (old & ~(mask)) \| (new & *mask)
		* bitmap_remap(dst, src, old, new, nbits) *dst = map(old, new)(src)
		* bitmap_bitremap(oldbit, old, new, nbits) newbit = map(old, new)(oldbit)
		@@ -133,6 +134,9 @@ extern void __bitmap_shift_right(unsigned long dst, const unsigned long src,
		unsigned int shift, unsigned int nbits);
		extern void __bitmap_shift_left(unsigned long dst, const unsigned long src,
		unsigned int shift, unsigned int nbits);
		extern void bitmap_cut(unsigned long dst, const unsigned long src,
		unsigned int first, unsigned int cut,
		unsigned int nbits);
		extern int __bitmap_and(unsigned long dst, const unsigned long bitmap1,
		const unsigned long *bitmap2, unsigned int nbits);
		extern void __bitmap_or(unsigned long dst, const unsigned long bitmap1,

lib/bitmap.c

+66 −0

Original line number	Diff line number	Diff line
		@@ -168,6 +168,72 @@ void __bitmap_shift_left(unsigned long dst, const unsigned long src,
		}
		EXPORT_SYMBOL(__bitmap_shift_left);

		/**
		* bitmap_cut() - remove bit region from bitmap and right shift remaining bits
		* @dst: destination bitmap, might overlap with src
		* @src: source bitmap
		* @first: start bit of region to be removed
		* @cut: number of bits to remove
		* @nbits: bitmap size, in bits
		*
		* Set the n-th bit of @dst iff the n-th bit of @src is set and
		* n is less than @first, or the m-th bit of @src is set for any
		* m such that @first <= n < nbits, and m = n + @cut.
		*
		* In pictures, example for a big-endian 32-bit architecture:
		*
		* @src:
		* 31 63
		* \| \|
		* 10000000 11000001 11110010 00010101 10000000 11000001 01110010 00010101
		* \| \| \| \|
		* 16 14 0 32
		*
		* if @cut is 3, and @first is 14, bits 14-16 in @src are cut and @dst is:
		*
		* 31 63
		* \| \|
		* 10110000 00011000 00110010 00010101 00010000 00011000 00101110 01000010
		* \| \| \|
		* 14 (bit 17 0 32
		* from @src)
		*
		* Note that @dst and @src might overlap partially or entirely.
		*
		* This is implemented in the obvious way, with a shift and carry
		* step for each moved bit. Optimisation is left as an exercise
		* for the compiler.
		*/
		void bitmap_cut(unsigned long dst, const unsigned long src,
		unsigned int first, unsigned int cut, unsigned int nbits)
		{
		unsigned int len = BITS_TO_LONGS(nbits);
		unsigned long keep = 0, carry;
		int i;

		memmove(dst, src, len * sizeof(*dst));

		if (first % BITS_PER_LONG) {
		keep = src[first / BITS_PER_LONG] &
		(~0UL >> (BITS_PER_LONG - first % BITS_PER_LONG));
		}

		while (cut--) {
		for (i = first / BITS_PER_LONG; i < len; i++) {
		if (i < len - 1)
		carry = dst[i + 1] & 1UL;
		else
		carry = 0;

		dst[i] = (dst[i] >> 1) \| (carry << (BITS_PER_LONG - 1));
		}
		}

		dst[first / BITS_PER_LONG] &= ~0UL << (first % BITS_PER_LONG);
		dst[first / BITS_PER_LONG] \|= keep;
		}
		EXPORT_SYMBOL(bitmap_cut);

		int __bitmap_and(unsigned long dst, const unsigned long bitmap1,
		const unsigned long *bitmap2, unsigned int bits)
		{

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