Line data    Source code

       1             : // SPDX-License-Identifier: GPL-2.0
       2             : #include <linux/bitops.h>
       3             : #include <linux/bug.h>
       4             : #include <linux/export.h>
       5             : #include <linux/limits.h>
       6             : #include <linux/math.h>
       7             : #include <linux/minmax.h>
       8             : #include <linux/types.h>
       9             : 
      10             : #include <linux/reciprocal_div.h>
      11             : 
      12             : /*
      13             :  * For a description of the algorithm please have a look at
      14             :  * include/linux/reciprocal_div.h
      15             :  */
      16             : 
      17          53 : struct reciprocal_value reciprocal_value(u32 d)
      18             : {
      19             :         struct reciprocal_value R;
      20             :         u64 m;
      21             :         int l;
      22             : 
      23         106 :         l = fls(d - 1);
      24          53 :         m = ((1ULL << 32) * ((1ULL << l) - d));
      25          53 :         do_div(m, d);
      26          53 :         ++m;
      27          53 :         R.m = (u32)m;
      28          53 :         R.sh1 = min(l, 1);
      29          53 :         R.sh2 = max(l - 1, 0);
      30             : 
      31          53 :         return R;
      32             : }
      33             : EXPORT_SYMBOL(reciprocal_value);
      34             : 
      35           0 : struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec)
      36             : {
      37             :         struct reciprocal_value_adv R;
      38             :         u32 l, post_shift;
      39             :         u64 mhigh, mlow;
      40             : 
      41             :         /* ceil(log2(d)) */
      42           0 :         l = fls(d - 1);
      43             :         /* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to
      44             :          * be handled before calling "reciprocal_value_adv", please see the
      45             :          * comment at include/linux/reciprocal_div.h.
      46             :          */
      47           0 :         WARN(l == 32,
      48             :              "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",
      49             :              d, __func__);
      50           0 :         post_shift = l;
      51           0 :         mlow = 1ULL << (32 + l);
      52           0 :         do_div(mlow, d);
      53           0 :         mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));
      54           0 :         do_div(mhigh, d);
      55             : 
      56           0 :         for (; post_shift > 0; post_shift--) {
      57           0 :                 u64 lo = mlow >> 1, hi = mhigh >> 1;
      58             : 
      59           0 :                 if (lo >= hi)
      60             :                         break;
      61             : 
      62           0 :                 mlow = lo;
      63           0 :                 mhigh = hi;
      64             :         }
      65             : 
      66           0 :         R.m = (u32)mhigh;
      67           0 :         R.sh = post_shift;
      68           0 :         R.exp = l;
      69           0 :         R.is_wide_m = mhigh > U32_MAX;
      70             : 
      71           0 :         return R;
      72             : }
      73             : EXPORT_SYMBOL(reciprocal_value_adv);