| 1 | |
| 2 | #include <linux/bitops.h>
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| 3 | #include <linux/bug.h>
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| 4 | #include <linux/export.h>
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| 5 | #include <linux/limits.h>
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| 6 | #include <linux/math.h>
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| 7 | #include <linux/minmax.h>
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| 8 | #include <linux/types.h>
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| 9 |
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| 10 | #include <linux/reciprocal_div.h>
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| 11 |
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| 12 | |
| 13 | * For a description of the algorithm please have a look at
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| 14 | * include/linux/reciprocal_div.h
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| 15 |
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| 16 |
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| 17 | struct reciprocal_value reciprocal_value(u32 d)
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| 18 | {
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| 19 | struct reciprocal_value R;
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| 20 | u64 m;
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| 21 | int l;
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| 22 |
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| 23 | l = fls(d - 1);
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| 24 | m = ((1ULL << 32) * ((1ULL << l) - d));
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| 25 | do_div(m, d);
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| 26 | ++m;
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| 27 | R.m = (u32)m;
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| 28 | R.sh1 = min(l, 1);
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| 29 | R.sh2 = max(l - 1, 0);
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| 30 |
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| 31 | return R;
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| 32 | }
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| 33 | EXPORT_SYMBOL(reciprocal_value);
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| 34 |
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| 35 | struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec)
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| 36 | {
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| 37 | struct reciprocal_value_adv R;
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| 38 | u32 l, post_shift;
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| 39 | u64 mhigh, mlow;
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| 40 |
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| 41 |
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| 42 | l = fls(d - 1);
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| 43 | |
| 44 | * be handled before calling "reciprocal_value_adv", please see the
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| 45 | * comment at include/linux/reciprocal_div.h.
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| 46 |
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| 47 | WARN(l == 32,
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| 48 | "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",
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| 49 | d, __func__);
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| 50 | post_shift = l;
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| 51 | mlow = 1ULL << (32 + l);
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| 52 | do_div(mlow, d);
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| 53 | mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));
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| 54 | do_div(mhigh, d);
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| 55 |
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| 56 | for (; post_shift > 0; post_shift--) {
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| 57 | u64 lo = mlow >> 1, hi = mhigh >> 1;
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| 58 |
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| 59 | if (lo >= hi)
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| 60 | break;
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| 61 |
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| 62 | mlow = lo;
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| 63 | mhigh = hi;
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| 64 | }
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| 65 |
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| 66 | R.m = (u32)mhigh;
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| 67 | R.sh = post_shift;
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| 68 | R.exp = l;
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| 69 | R.is_wide_m = mhigh > U32_MAX;
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| 70 |
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| 71 | return R;
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| 72 | }
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| 73 | EXPORT_SYMBOL(reciprocal_value_adv);
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