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