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From: David Hildenbrand <david@redhat.com>
Message-ID: <6ac53abd-d461-e1f3-8e34-06f8584e85fc@redhat.com>
Date: Mon, 25 Feb 2019 17:17:09 +0100
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Subject: Re: [Qemu-devel] [PATCH v1 7/7] s390x/tcg: Implement LOAD COUNT TO
 BLOCK BOUNDARY
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To: Richard Henderson <richard.henderson@linaro.org>, qemu-devel@nongnu.org
Cc: qemu-s390x@nongnu.org, Cornelia Huck <cohuck@redhat.com>, Thomas Huth <thuth@redhat.com>, Richard Henderson <rth@twiddle.net>

On 25.02.19 17:14, Richard Henderson wrote:
> On 2/25/19 3:55 AM, David Hildenbrand wrote:
>> +uint64_t HELPER(lcbb)(uint64_t addr, uint32_t m3)
>> +{
>> +    const uint32_t block_size = 1ul << (m3 + 6);
>> +    const uint64_t rounded_addr = ROUND_UP(addr, block_size);
>> +    uint32_t to_load = 16;
>> +
>> +    if (rounded_addr != addr) {
>> +        to_load = MIN(rounded_addr - addr, to_load);
>> +    }
>> +    return to_load;
>> +}
> 
> I don't understand all of this "blocksize" business, when they are all powers
> of two, and the maximum value returned is 16.
> 
> As far as I can see, the result is obtained by -(addr | -16) regardless of the
> value of m3.

Let's assume we have addr = 63;

Assume block size is 64:
-> to_load = 1

Assume block size is 128:
-> to_load = 16

Or am i missing something?

-- 

Thanks,

David / dhildenb