linux-kernel - Re: [PATCH 2/3] lib: zlib_inflate: improves decompression performance

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Date:   Thu, 12 Nov 2020 01:06:32 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Zhaoxiu Zeng <zengzhaoxiu@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>
Subject: Re: [PATCH 2/3] lib: zlib_inflate: improves decompression performance

On Wed, Nov 11, 2020 at 5:06 PM Zhaoxiu Zeng <zengzhaoxiu@....com> wrote:
> 在 2020/11/11 11:46, Jann Horn 写道:
> > On Mon, Nov 9, 2020 at 8:27 PM <zengzhaoxiu@....com> wrote:
> >> This patch does:
> >> 1. Cleanup code and reduce branches
> >> 2. Use copy_from_back to copy the matched bytes from the back output buffer
> >
> > What exactly is copy_from_back()? Is it like memmove()? If yes, have
> > you tried using memmove() instead of the code added in patch 1/3?
> >
>
> If use memcpy(or memmove), the code will be like this:
>         while (dist < len) {
>                 memcpy(out, out - dist, dist);
>                 out += dist;
>                 len -= dist;
>         }
>         memcpy(out, out - dist, len);

Ah, thanks. So basically it means: "repeatedly copy a pattern of
length `dist` from `out-dist` to `out` until `len` bytes have been
written"