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| 3 | * Generic polynomial calculation using integer coefficients.
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| 4 | *
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| 5 | * Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
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| 6 | *
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| 7 | * Authors:
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| 8 | * Maxim Kaurkin <[email protected]>
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| 9 | * Serge Semin <[email protected]>
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| 10 | *
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| 11 |
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| 12 |
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| 13 | #include <linux/kernel.h>
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| 14 | #include <linux/module.h>
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| 15 | #include <linux/polynomial.h>
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| 16 |
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| 17 | |
| 18 | * Originally this was part of drivers/hwmon/bt1-pvt.c.
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| 19 | * There the following conversion is used and should serve as an example here:
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| 20 | *
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| 21 | * The original translation formulae of the temperature (in degrees of Celsius)
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| 22 | * to PVT data and vice-versa are following:
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| 23 | *
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| 24 | * N = 1.8322e-8*(T^4) + 2.343e-5*(T^3) + 8.7018e-3*(T^2) + 3.9269*(T^1) +
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| 25 | * 1.7204e2
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| 26 | * T = -1.6743e-11*(N^4) + 8.1542e-8*(N^3) + -1.8201e-4*(N^2) +
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| 27 | * 3.1020e-1*(N^1) - 4.838e1
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| 28 | *
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| 29 | * where T = [-48.380, 147.438]C and N = [0, 1023].
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| 30 | *
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| 31 | * They must be accordingly altered to be suitable for the integer arithmetics.
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| 32 | * The technique is called 'factor redistribution', which just makes sure the
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| 33 | * multiplications and divisions are made so to have a result of the operations
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| 34 | * within the integer numbers limit. In addition we need to translate the
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| 35 | * formulae to accept millidegrees of Celsius. Here what they look like after
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| 36 | * the alterations:
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| 37 | *
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| 38 | * N = (18322e-20*(T^4) + 2343e-13*(T^3) + 87018e-9*(T^2) + 39269e-3*T +
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| 39 | * 17204e2) / 1e4
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| 40 | * T = -16743e-12*(D^4) + 81542e-9*(D^3) - 182010e-6*(D^2) + 310200e-3*D -
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| 41 | * 48380
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| 42 | * where T = [-48380, 147438] mC and N = [0, 1023].
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| 43 | *
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| 44 | * static const struct polynomial poly_temp_to_N = {
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| 45 | * .total_divider = 10000,
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| 46 | * .terms = {
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| 47 | * {4, 18322, 10000, 10000},
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| 48 | * {3, 2343, 10000, 10},
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| 49 | * {2, 87018, 10000, 10},
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| 50 | * {1, 39269, 1000, 1},
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| 51 | * {0, 1720400, 1, 1}
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| 52 | * }
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| 53 | * };
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| 54 | *
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| 55 | * static const struct polynomial poly_N_to_temp = {
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| 56 | * .total_divider = 1,
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| 57 | * .terms = {
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| 58 | * {4, -16743, 1000, 1},
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| 59 | * {3, 81542, 1000, 1},
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| 60 | * {2, -182010, 1000, 1},
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| 61 | * {1, 310200, 1000, 1},
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| 62 | * {0, -48380, 1, 1}
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| 63 | * }
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| 64 | * };
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| 65 |
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| 66 |
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| 67 | |
| 68 | * polynomial_calc - calculate a polynomial using integer arithmetic
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| 69 | *
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| 70 | * @poly: pointer to the descriptor of the polynomial
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| 71 | * @data: input value of the polynimal
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| 72 | *
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| 73 | * Calculate the result of a polynomial using only integer arithmetic. For
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| 74 | * this to work without too much loss of precision the coefficients has to
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| 75 | * be altered. This is called factor redistribution.
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| 76 | *
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| 77 | * Returns the result of the polynomial calculation.
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| 78 |
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| 79 | long polynomial_calc(const struct polynomial *poly, long data)
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| 80 | {
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| 81 | const struct polynomial_term *term = poly->terms;
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| 82 | long total_divider = poly->total_divider ?: 1;
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| 83 | long tmp, ret = 0;
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| 84 | int deg;
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| 85 |
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| 86 | |
| 87 | * Here is the polynomial calculation function, which performs the
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| 88 | * redistributed terms calculations. It's pretty straightforward.
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| 89 | * We walk over each degree term up to the free one, and perform
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| 90 | * the redistributed multiplication of the term coefficient, its
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| 91 | * divider (as for the rationale fraction representation), data
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| 92 | * power and the rational fraction divider leftover. Then all of
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| 93 | * this is collected in a total sum variable, which value is
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| 94 | * normalized by the total divider before being returned.
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| 95 |
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| 96 | do {
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| 97 | tmp = term->coef;
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| 98 | for (deg = 0; deg < term->deg; ++deg)
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| 99 | tmp = mult_frac(tmp, data, term->divider);
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| 100 | ret += tmp / term->divider_leftover;
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| 101 | } while ((term++)->deg);
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| 102 |
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| 103 | return ret / total_divider;
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| 104 | }
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| 105 | EXPORT_SYMBOL_GPL(polynomial_calc);
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| 106 |
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| 107 | MODULE_DESCRIPTION("Generic polynomial calculations");
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| 108 | MODULE_LICENSE("GPL");
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