[ovs-dev] [bug10576 1/5] util: New function bitwise_one().

[Ethan Jackson]

Looks good, thanks.

Ethan

On Wed, Apr 11, 2012 at 17:15, Ben Pfaff <blp at nicira.com> wrote:
> It's the obvious counterpart to bitwise_zero().
>
> Signed-off-by: Ben Pfaff <blp at nicira.com>
> ---
>  lib/util.c        |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  lib/util.h        |    2 ++
>  tests/library.at  |    3 ++-
>  tests/test-util.c |   43 +++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 95 insertions(+), 1 deletions(-)
>
> diff --git a/lib/util.c b/lib/util.c
> index 810d766..14a97f2 100644
> --- a/lib/util.c
> +++ b/lib/util.c
> @@ -865,6 +865,54 @@ bitwise_zero(void *dst_, unsigned int dst_len, unsigned dst_ofs,
>     }
>  }
>
> +/* Sets to 1 all of the 'n_bits' bits starting from bit 'dst_ofs' in 'dst'.
> + * 'dst' is 'dst_len' bytes long.
> + *
> + * If you consider all of 'dst' to be a single unsigned integer in network byte
> + * order, then bit N is the bit with value 2**N.  That is, bit 0 is the bit
> + * with value 1 in dst[dst_len - 1], bit 1 is the bit with value 2, bit 2 is
> + * the bit with value 4, ..., bit 8 is the bit with value 1 in dst[dst_len -
> + * 2], and so on.
> + *
> + * Required invariant:
> + *   dst_ofs + n_bits <= dst_len * 8
> + */
> +void
> +bitwise_one(void *dst_, unsigned int dst_len, unsigned dst_ofs,
> +            unsigned int n_bits)
> +{
> +    uint8_t *dst = dst_;
> +
> +    if (!n_bits) {
> +        return;
> +    }
> +
> +    dst += dst_len - (dst_ofs / 8 + 1);
> +    dst_ofs %= 8;
> +
> +    if (dst_ofs) {
> +        unsigned int chunk = MIN(n_bits, 8 - dst_ofs);
> +
> +        *dst |= ((1 << chunk) - 1) << dst_ofs;
> +
> +        n_bits -= chunk;
> +        if (!n_bits) {
> +            return;
> +        }
> +
> +        dst--;
> +    }
> +
> +    while (n_bits >= 8) {
> +        *dst-- = 0xff;
> +        n_bits -= 8;
> +    }
> +
> +    if (n_bits) {
> +        *dst |= (1 << n_bits) - 1;
> +    }
> +}
> +
>  /* Copies the 'n_bits' low-order bits of 'value' into the 'n_bits' bits
>  * starting at bit 'dst_ofs' in 'dst', which is 'dst_len' bytes long.
>  *
> diff --git a/lib/util.h b/lib/util.h
> index bdad501..63f4a24 100644
> --- a/lib/util.h
> +++ b/lib/util.h
> @@ -228,6 +228,8 @@ void bitwise_copy(const void *src, unsigned int src_len, unsigned int src_ofs,
>                   unsigned int n_bits);
>  void bitwise_zero(void *dst_, unsigned int dst_len, unsigned dst_ofs,
>                   unsigned int n_bits);
> +void bitwise_one(void *dst_, unsigned int dst_len, unsigned dst_ofs,
> +                 unsigned int n_bits);
>  void bitwise_put(uint64_t value,
>                  void *dst, unsigned int dst_len, unsigned int dst_ofs,
>                  unsigned int n_bits);
> diff --git a/tests/library.at b/tests/library.at
> index ca5f29c..dce69de 100644
> --- a/tests/library.at
> +++ b/tests/library.at
> @@ -100,7 +100,8 @@ nibble   0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15
>  ])
>  AT_CLEANUP
>
> -AT_SETUP([test log_2_floor])
> +AT_SETUP([test utility functions])
> +AT_KEYWORDS([util])
>  AT_CHECK([test-util])
>  AT_CLEANUP
>
> diff --git a/tests/test-util.c b/tests/test-util.c
> index 82d0861..ed98295 100644
> --- a/tests/test-util.c
> +++ b/tests/test-util.c
> @@ -143,6 +143,47 @@ check_bitwise_zero(void)
>     }
>  }
>
> +static void
> +check_bitwise_one(void)
> +{
> +    unsigned int n_loops;
> +    int dst_ofs;
> +    int n_bits;
> +
> +    n_loops = 0;
> +    for (n_bits = 0; n_bits <= 64; n_bits++) {
> +        for (dst_ofs = 0; dst_ofs < 64 - n_bits; dst_ofs++) {
> +            ovs_be64 dst = htonll(random_uint64());
> +            ovs_be64 orig_dst = dst;
> +            ovs_be64 expect;
> +
> +            if (n_bits == 64) {
> +                expect = htonll(UINT64_MAX);
> +            } else {
> +                uint64_t mask = (UINT64_C(1) << n_bits) - 1;
> +                expect = orig_dst | htonll(mask << dst_ofs);
> +            }
> +
> +            bitwise_one(&dst, sizeof dst, dst_ofs, n_bits);
> +            if (expect != dst) {
> +                fprintf(stderr,"bitwise_one(0x%016"PRIx64",8,%d, %d) "
> +                        "yielded 0x%016"PRIx64" "
> +                        "instead of the expected 0x%016"PRIx64"\n",
> +                        ntohll(orig_dst), dst_ofs,
> +                        n_bits,
> +                        ntohll(dst), ntohll(expect));
> +                abort();
> +            }
> +
> +            n_loops++;
> +        }
> +    }
> +
> +    if (n_loops != 64 * (64 + 1) / 2) {
> +        abort();
> +    }
> +}
> +
>  int
>  main(void)
>  {
> @@ -170,5 +211,7 @@ main(void)
>
>     check_bitwise_zero();
>
> +    check_bitwise_one();
> +
>     return 0;
>  }
> --
> 1.7.2.5
>
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