linux-kernel - Re: [PATCH v9 1/3] lib: Add strongly typed 64bit int

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Date:   Wed, 20 Dec 2017 15:19:38 +0100
From:   Crt Mori <cmo@...exis.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Ian Abbott <abbotti@....co.uk>,
        Larry Finger <Larry.Finger@...inger.net>,
        Niklas Soderlund <niklas.soderlund+renesas@...natech.se>,
        Thomas Gleixner <tglx@...utronix.de>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org,
        Linux Iio <linux-iio@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v9 1/3] lib: Add strongly typed 64bit int_sqrt

On 20 December 2017 at 10:56, Joe Perches <joe@...ches.com> wrote:
> On Wed, 2017-12-20 at 10:33 +0100, Crt Mori wrote:
>> There is no option to perform 64bit integer sqrt on 32bit platform.
>> Added stronger typed int_sqrt64 enables the 64bit calculations to
>> be performed on 32bit platforms. Although int_sqrt() is a rough
>> approximation, the same algorithm is used in int_sqrt64() as good
>> enough on 32bit platform.
> []
>> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> []
>> @@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr);
>>  extern int func_ptr_is_kernel_text(void *ptr);
>>
>>  unsigned long int_sqrt(unsigned long);
>> +u32 int_sqrt64(u64 x);
>
> #ifdef BITS_PER_LONG == 64
> static inline u32 int_sqrt64(u64 x)
> {
>         re
> turn (u32)int_sqrt(x);
> }
> #else
> u32 int_sqrt64(u64 x);
> #endif
>
> []
>

OK, fixing it in v10.

>> +#if BITS_PER_LONG < 64
>> +/**
>> + * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
>> + * is expected.
>> + * @x: 64bit integer of which to calculate the sqrt
>> + */
>> +u32 int_sqrt64(u64 x)
>> +{
>> +     u64 b, m, y = 0;
>> +
>> +     if (x <= 1)
>> +             return x;
>> +
>> +     m = 1ULL << (fls64(x) & ~1ULL);
>> +     while (m != 0) {
>> +             b = y + m;
>> +             y >>= 1;
>> +
>> +             if (x >= b) {
>> +                     x -= b;
>> +                     y += m;
>> +             }
>> +             m >>= 2;
>> +     }
>> +
>> +     return y;
>> +}
>> +EXPORT_SYMBOL(int_sqrt64);
>> +#else
>> +u32 int_sqrt64(u64 x)
>> +{
>> +     return int_sqrt(x);
>> +}
>> +EXPORT_SYMBOL(int_sqrt64);
>> +#endif
>
> This doesn't need to be EXPORT_SYMBOL for the
> BITS_PER_LONG == 64 case
>