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