diff options
Diffstat (limited to 'lib/bitmap.c')
| -rw-r--r-- | lib/bitmap.c | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/lib/bitmap.c b/lib/bitmap.c index 4250519d7d1c..6e175fbd69a9 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -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) { |