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Re: [PATCH] aarch64: Optimized memset for Kunpeng processor.
- From: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- To: "Zhangxuelei (Derek)" <zhangxuelei4 at huawei dot com>, "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>, "siddhesh at gotplt dot org" <siddhesh at gotplt dot org>, Szabolcs Nagy <Szabolcs dot Nagy at arm dot com>, jiangyikun <jiangyikun at huawei dot com>, "yikunkero at gmail dot com" <yikunkero at gmail dot com>
- Cc: nd <nd at arm dot com>
- Date: Thu, 31 Oct 2019 16:04:21 +0000
- Subject: Re: [PATCH] aarch64: Optimized memset for Kunpeng processor.
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Hi Derek,
> Here the setting inerval if 64..127 bytes rather than 64..96 bytes, so if no branch,
> the 64..80 bytes setting will beyond the border using dstend. And the interval
> became longer just can benefit 96..127 bytes.
For the 64..128 case it is always safe to copy 64 bytes from the start and 64 bytes
from the end - the tail overlap means you never can go outside the bounds.
Generally it's faster that way due to avoiding unnecessary branches which may mispredict.
Wilco