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Date: Sun, 8 Jul 2012 20:32:59 +0100
Message-ID: <CAFEAcA_oTrA2Z+W2PVY40CA=rM_+=Ru+knbEQPWMrPnq4OmmHw@mail.gmail.com>
From: Peter Maydell <peter.maydell@linaro.org>
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Subject: Re: [Qemu-devel] [PATCH] bitops: fix types
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: qemu-devel@nongnu.org

On 8 July 2012 20:12, Blue Swirl <blauwirbel@gmail.com> wrote:
> On Sun, Jul 8, 2012 at 6:54 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
>> On 8 July 2012 19:32, Blue Swirl <blauwirbel@gmail.com> wrote:
>>> On Sun, Jul 8, 2012 at 2:04 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
>>>> On 8 July 2012 13:12,  <blauwirbel@gmail.com> wrote:
>>>>> -static inline uint64_t deposit64(uint64_t value, int start, int length,
>>>>> -                                 uint64_t fieldval)
>>>>> +static inline uint64_t deposit64(uint64_t value, unsigned int start,
>>>>> +                                 unsigned int length, uint64_t fieldval)
>>>>>  {
>>>>>      uint64_t mask;
>>>>> -    assert(start >= 0 && length > 0 && length <= 64 - start);
>>>>> +    assert(length > 0 && length <= 64 - start);
>>>>
>>>> This breaks the assertion (consider the case of start == UINT_MAX
>>>> and length == 64).
>>>
>>> The original is equally buggy in other cases since there is no bound
>>> check for the upper limit.
>>
>> For what upper limit? Overlong length or start should both be caught
>> by the third condition in the signed case.
>
> Nice. Why is it written like that, I'd use
> start + length <= 64?

That would fail to handle the case of start == length == INT_MAX.

-- PMM