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| -rw-r--r-- | lib/polynomial.c | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/lib/polynomial.c b/lib/polynomial.c new file mode 100644 index 000000000..66d383445 --- /dev/null +++ b/lib/polynomial.c @@ -0,0 +1,108 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Generic polynomial calculation using integer coefficients. + * + * Copyright (C) 2020 BAIKAL ELECTRONICS, JSC + * + * Authors: + * Maxim Kaurkin <maxim.kaurkin@baikalelectronics.ru> + * Serge Semin <Sergey.Semin@baikalelectronics.ru> + * + */ + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/polynomial.h> + +/* + * Originally this was part of drivers/hwmon/bt1-pvt.c. + * There the following conversion is used and should serve as an example here: + * + * The original translation formulae of the temperature (in degrees of Celsius) + * to PVT data and vice-versa are following: + * + * N = 1.8322e-8*(T^4) + 2.343e-5*(T^3) + 8.7018e-3*(T^2) + 3.9269*(T^1) + + * 1.7204e2 + * T = -1.6743e-11*(N^4) + 8.1542e-8*(N^3) + -1.8201e-4*(N^2) + + * 3.1020e-1*(N^1) - 4.838e1 + * + * where T = [-48.380, 147.438]C and N = [0, 1023]. + * + * They must be accordingly altered to be suitable for the integer arithmetics. + * The technique is called 'factor redistribution', which just makes sure the + * multiplications and divisions are made so to have a result of the operations + * within the integer numbers limit. In addition we need to translate the + * formulae to accept millidegrees of Celsius. Here what they look like after + * the alterations: + * + * N = (18322e-20*(T^4) + 2343e-13*(T^3) + 87018e-9*(T^2) + 39269e-3*T + + * 17204e2) / 1e4 + * T = -16743e-12*(D^4) + 81542e-9*(D^3) - 182010e-6*(D^2) + 310200e-3*D - + * 48380 + * where T = [-48380, 147438] mC and N = [0, 1023]. + * + * static const struct polynomial poly_temp_to_N = { + * .total_divider = 10000, + * .terms = { + * {4, 18322, 10000, 10000}, + * {3, 2343, 10000, 10}, + * {2, 87018, 10000, 10}, + * {1, 39269, 1000, 1}, + * {0, 1720400, 1, 1} + * } + * }; + * + * static const struct polynomial poly_N_to_temp = { + * .total_divider = 1, + * .terms = { + * {4, -16743, 1000, 1}, + * {3, 81542, 1000, 1}, + * {2, -182010, 1000, 1}, + * {1, 310200, 1000, 1}, + * {0, -48380, 1, 1} + * } + * }; + */ + +/** + * polynomial_calc - calculate a polynomial using integer arithmetic + * + * @poly: pointer to the descriptor of the polynomial + * @data: input value of the polynimal + * + * Calculate the result of a polynomial using only integer arithmetic. For + * this to work without too much loss of precision the coefficients has to + * be altered. This is called factor redistribution. + * + * Returns the result of the polynomial calculation. + */ +long polynomial_calc(const struct polynomial *poly, long data) +{ + const struct polynomial_term *term = poly->terms; + long total_divider = poly->total_divider ?: 1; + long tmp, ret = 0; + int deg; + + /* + * Here is the polynomial calculation function, which performs the + * redistributed terms calculations. It's pretty straightforward. + * We walk over each degree term up to the free one, and perform + * the redistributed multiplication of the term coefficient, its + * divider (as for the rationale fraction representation), data + * power and the rational fraction divider leftover. Then all of + * this is collected in a total sum variable, which value is + * normalized by the total divider before being returned. + */ + do { + tmp = term->coef; + for (deg = 0; deg < term->deg; ++deg) + tmp = mult_frac(tmp, data, term->divider); + ret += tmp / term->divider_leftover; + } while ((term++)->deg); + + return ret / total_divider; +} +EXPORT_SYMBOL_GPL(polynomial_calc); + +MODULE_DESCRIPTION("Generic polynomial calculations"); +MODULE_LICENSE("GPL"); |