74 lines
1.5 KiB
C
74 lines
1.5 KiB
C
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// 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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