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       1                 :            : // SPDX-License-Identifier: GPL-2.0
       2                 :            : #include <linux/bug.h>
       3                 :            : #include <linux/kernel.h>
       4                 :            : #include <asm/div64.h>
       5                 :            : #include <linux/reciprocal_div.h>
       6                 :            : #include <linux/export.h>
       7                 :            : 
       8                 :            : /*
       9                 :            :  * For a description of the algorithm please have a look at
      10                 :            :  * include/linux/reciprocal_div.h
      11                 :            :  */
      12                 :            : 
      13                 :          0 : struct reciprocal_value reciprocal_value(u32 d)
      14                 :            : {
      15                 :            :         struct reciprocal_value R;
      16                 :            :         u64 m;
      17                 :            :         int l;
      18                 :            : 
      19                 :          0 :         l = fls(d - 1);
      20                 :          0 :         m = ((1ULL << 32) * ((1ULL << l) - d));
      21   [ #  #  #  #  :          0 :         do_div(m, d);
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      22                 :          0 :         ++m;
      23                 :          0 :         R.m = (u32)m;
      24                 :          0 :         R.sh1 = min(l, 1);
      25                 :          0 :         R.sh2 = max(l - 1, 0);
      26                 :            : 
      27                 :          0 :         return R;
      28                 :            : }
      29                 :            : EXPORT_SYMBOL(reciprocal_value);
      30                 :            : 
      31                 :          0 : struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec)
      32                 :            : {
      33                 :            :         struct reciprocal_value_adv R;
      34                 :            :         u32 l, post_shift;
      35                 :            :         u64 mhigh, mlow;
      36                 :            : 
      37                 :            :         /* ceil(log2(d)) */
      38                 :          0 :         l = fls(d - 1);
      39                 :            :         /* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to
      40                 :            :          * be handled before calling "reciprocal_value_adv", please see the
      41                 :            :          * comment at include/linux/reciprocal_div.h.
      42                 :            :          */
      43         [ #  # ]:          0 :         WARN(l == 32,
      44                 :            :              "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",
      45                 :            :              d, __func__);
      46                 :            :         post_shift = l;
      47                 :          0 :         mlow = 1ULL << (32 + l);
      48   [ #  #  #  #  :          0 :         do_div(mlow, d);
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      49                 :          0 :         mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));
      50   [ #  #  #  #  :          0 :         do_div(mhigh, d);
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      51                 :            : 
      52         [ #  # ]:          0 :         for (; post_shift > 0; post_shift--) {
      53                 :          0 :                 u64 lo = mlow >> 1, hi = mhigh >> 1;
      54                 :            : 
      55         [ #  # ]:          0 :                 if (lo >= hi)
      56                 :            :                         break;
      57                 :            : 
      58                 :          0 :                 mlow = lo;
      59                 :          0 :                 mhigh = hi;
      60                 :            :         }
      61                 :            : 
      62                 :          0 :         R.m = (u32)mhigh;
      63                 :          0 :         R.sh = post_shift;
      64                 :          0 :         R.exp = l;
      65                 :          0 :         R.is_wide_m = mhigh > U32_MAX;
      66                 :            : 
      67                 :          0 :         return R;
      68                 :            : }
      69                 :            : EXPORT_SYMBOL(reciprocal_value_adv);