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// SPDX-License-Identifier: GPL-2.0
#include <linux/bug.h>
#include <linux/kernel.h>
#include <asm/div64.h>
#include <linux/reciprocal_div.h>
#include <linux/export.h>
/*
* For a description of the algorithm please have a look at
* include/linux/reciprocal_div.h
*/
struct reciprocal_value reciprocal_value(u32 d)
{
struct reciprocal_value R;
u64 m;
int l;
l = fls(d - 1);
m = ((1ULL << 32) * ((1ULL << l) - d));
do_div(m, d);
++m;
R.m = (u32)m;
R.sh1 = min(l, 1);
R.sh2 = max(l - 1, 0);
return R;
}
EXPORT_SYMBOL(reciprocal_value);
struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec)
{
struct reciprocal_value_adv R;
u32 l, post_shift;
u64 mhigh, mlow;
/* ceil(log2(d)) */
l = fls(d - 1);
/* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to
* be handled before calling "reciprocal_value_adv", please see the
* comment at include/linux/reciprocal_div.h.
*/
WARN(l == 32,
"ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",
d, __func__);
post_shift = l;
mlow = 1ULL << (32 + l);
do_div(mlow, d);
mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));
do_div(mhigh, d);
for (; post_shift > 0; post_shift--) {
u64 lo = mlow >> 1, hi = mhigh >> 1;
if (lo >= hi)
break;
mlow = lo;
mhigh = hi;
}
R.m = (u32)mhigh;
R.sh = post_shift;
R.exp = l;
R.is_wide_m = mhigh > U32_MAX;
return R;
}
EXPORT_SYMBOL(reciprocal_value_adv);
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