Messages in this thread | | | Date | Mon, 10 Oct 2022 19:53:51 +0200 | From | "Jason A. Donenfeld" <> | Subject | Re: [crng-random:jd/get_random_u32_below 23/23] include/linux/random.h:64:69: sparse: sparse: cast truncates bits from constant value (1f4 becomes f4) |
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On Mon, Oct 10, 2022 at 05:18:40PM +0000, David Laight wrote: > From: kernel test robot <lkp@intel.com> > > Sent: 10 October 2022 00:32 > > To: Jason A. Donenfeld <zx2c4@kernel.org> > ... > > I'm missing the main mailing list email for this change. > I'm guessing the non-inlined code for non-constant ceil > is similar.
It's part of a development tree I already linked you to. It's not done yet. This alert is just about needing a __force.
> > > vim +64 include/linux/random.h > > > > 53 > > 54 u32 __get_random_u32_below(u32 ceil); > > 55 /* Returns a random integer in the interval [0, ceil), with uniform distribution. */ > > 56 static inline u32 get_random_u32_below(u32 ceil) > > 57 { > > 58 if (!__builtin_constant_p(ceil)) > > 59 return __get_random_u32_below(ceil); > > 60 > > 61 for (;;) { > > 62 if (ceil <= 1U << 8) { > > 63 u32 mult = ceil * get_random_u8(); > > > 64 if (is_power_of_2(ceil) || (u8)mult >= -(u8)ceil % ceil) > > 65 return mult >> 8; > > If you are going to check is_power_of_2() then you might as well do: > u32 val = get_random_u8(); > if (is_power_of_2(ceil)) > return ceil == 0x100 ? val : val & (ceil - 1); > Except that you don't want to loop on zero - so !(ceil & (ceil - 1))
I thought I opted out of the Laight drive-bys?
Either way, I don't understand your comments or how they pertain to the current code in that unfinished development branch. Please just send real patches.
Jason
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