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Re: [Qemu-devel] [RFC][PATCH 2/9] add a function to find non-zero conten
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC][PATCH 2/9] add a function to find non-zero content in a buffer |
Date: |
Tue, 12 Mar 2013 09:59:07 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3 |
On 03/12/2013 09:48 AM, Peter Lieven wrote:
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> include/qemu-common.h | 1 +
> util/cutils.c | 30 ++++++++++++++++++++++++++++++
> 2 files changed, 31 insertions(+)
>
>
> /*
> + * Searches for an area with non-zero content in a buffer
> + *
> + * Attention! The len must be a multiple of 8 * sizeof(VECTYPE)
> + * and addr must bedue to restriction of optimizations in this function.
s/bedue/be XXX due/
don't know what XXX is supposed to be. Instead of stating this in a
comment...
> + *
> + * The return value is the offset of the non-zero area rounded
> + * down to 8 * sizeof(VECTYPE). If the buffer is all zero
> + * the return value is equal to len.
> + */
> +
> +size_t buffer_find_nonzero_offset(const void *buf, size_t len)
> +{
...why not instead assert() it as part of the contract?
> + VECTYPE *p = (VECTYPE *)buf;
> + VECTYPE zero = ZERO_SPLAT;
> + size_t i;
> + for (i = 0; i < len / sizeof(VECTYPE); i += 8) {
> + VECTYPE tmp0 = p[i+0] | p[i+1];
> + VECTYPE tmp1 = p[i+2] | p[i+3];
> + VECTYPE tmp2 = p[i+4] | p[i+5];
> + VECTYPE tmp3 = p[i+6] | p[i+7];
> + VECTYPE tmp01 = tmp0 | tmp1;
> + VECTYPE tmp23 = tmp2 | tmp3;
> + if (!ALL_EQ(tmp01 | tmp23, zero)) {
> + break;
> + }
> + }
> + return i * sizeof(VECTYPE);
> +}
> +
> +/*
> * Checks if a buffer is all zeroes
> *
> * Attention! The len must be a multiple of 4 * sizeof(long) due to
oh, probably because of copy and paste.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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