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1// SPDX-License-Identifier: GPL-2.02#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 at14 * include/linux/reciprocal_div.h15 */16 17struct reciprocal_value reciprocal_value(u32 d)18{19 struct reciprocal_value R;20 u64 m;21 int l;22 23 l = fls(d - 1);24 m = ((1ULL << 32) * ((1ULL << l) - d));25 do_div(m, d);26 ++m;27 R.m = (u32)m;28 R.sh1 = min(l, 1);29 R.sh2 = max(l - 1, 0);30 31 return R;32}33EXPORT_SYMBOL(reciprocal_value);34 35struct 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 l = fls(d - 1);43 /* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to44 * be handled before calling "reciprocal_value_adv", please see the45 * comment at include/linux/reciprocal_div.h.46 */47 WARN(l == 32,48 "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",49 d, __func__);50 post_shift = l;51 mlow = 1ULL << (32 + l);52 do_div(mlow, d);53 mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));54 do_div(mhigh, d);55 56 for (; post_shift > 0; post_shift--) {57 u64 lo = mlow >> 1, hi = mhigh >> 1;58 59 if (lo >= hi)60 break;61 62 mlow = lo;63 mhigh = hi;64 }65 66 R.m = (u32)mhigh;67 R.sh = post_shift;68 R.exp = l;69 R.is_wide_m = mhigh > U32_MAX;70 71 return R;72}73EXPORT_SYMBOL(reciprocal_value_adv);74