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
13struct reciprocal_value reciprocal_value(u32 d)
14{
15	struct reciprocal_value R;
16	u64 m;
17	int l;
18
19	l = fls(d - 1);
20	m = ((1ULL << 32) * ((1ULL << l) - d));
21	do_div(m, d);
22	++m;
23	R.m = (u32)m;
24	R.sh1 = min(l, 1);
25	R.sh2 = max(l - 1, 0);
26
27	return R;
28}
29EXPORT_SYMBOL(reciprocal_value);
30
31struct 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	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	WARN(l == 32,
44	     "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",
45	     d, __func__);
46	post_shift = l;
47	mlow = 1ULL << (32 + l);
48	do_div(mlow, d);
49	mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));
50	do_div(mhigh, d);
51
52	for (; post_shift > 0; post_shift--) {
53		u64 lo = mlow >> 1, hi = mhigh >> 1;
54
55		if (lo >= hi)
56			break;
57
58		mlow = lo;
59		mhigh = hi;
60	}
61
62	R.m = (u32)mhigh;
63	R.sh = post_shift;
64	R.exp = l;
65	R.is_wide_m = mhigh > U32_MAX;
66
67	return R;
68}
69EXPORT_SYMBOL(reciprocal_value_adv);