Re: [Qemu-devel] [RFC v6 1/2] util: add memmem replacement function

[Eric Blake <eblake@redhat.com>]

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On 05/18/2015 05:22 AM, hw.claudio@gmail.com wrote:
> From: Claudio Fontana <claudio.fontana@huawei.com>
> 
> if the memmem function is missing, provide a trivial replacement.
> 
> Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
> ---
>  configure            | 15 +++++++++++++
>  include/qemu/osdep.h |  4 ++++
>  util/Makefile.objs   |  1 +
>  util/memmem.c        | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 82 insertions(+)
>  create mode 100644 util/memmem.c
> 

> +    if (s_len == 1) {
> +        return memchr(hay, s[0], hay_len);
> +    }
> +
> +    for (; hay <= last; hay++) {
> +        if (hay[0] == s[0] && memcmp(hay, s, s_len) == 0) {

An obvious optimization would be:

if (hay[0] == s[0] && memcmp(hay + 1, s + 1, s_len - 1) == 0)

since you already compared the first byte and know that the needle is
more than one byte.

But it's not worth the churn; this version is sufficient for the job as-is.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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