74 lines
1.5 KiB
C
74 lines
1.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
#include <linux/bitops.h>
|
|
#include <linux/bug.h>
|
|
#include <linux/export.h>
|
|
#include <linux/limits.h>
|
|
#include <linux/math.h>
|
|
#include <linux/minmax.h>
|
|
#include <linux/types.h>
|
|
|
|
#include <linux/reciprocal_div.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);
|