From e8dd273d199f5bbe295a8e3d8b777c5505b6b2e1 Mon Sep 17 00:00:00 2001 From: Salah Triki Date: Thu, 17 Sep 2026 14:00:52 +0100 Subject: iio: proximity: isl29501: Fix return type of isl29501_register_write isl29501_register_write() was returning a u32 instead of an int. Since the function returns negative error codes (such as -ERANGE or return values from i2c_smbus_write_byte_data()), returning an unsigned integer type prevents callers from correctly checking for negative error conditions. Fix this by changing the function return type from u32 to int. This was found through manual code review. Fixes: 1c28799257bc ("iio: light: isl29501: Add support for the ISL29501 ToF sensor.") Signed-off-by: Salah Triki Reviewed-by: Joshua Crofts Cc: stable@vger.kernel.org Signed-off-by: Jonathan Cameron --- lib/math/rational.c | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 lib/math/rational.c (limited to 'lib/math/rational.c') diff --git a/lib/math/rational.c b/lib/math/rational.c new file mode 100644 index 000000000..d2c34e629 --- /dev/null +++ b/lib/math/rational.c @@ -0,0 +1,112 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * rational fractions + * + * Copyright (C) 2009 emlix GmbH, Oskar Schirmer + * Copyright (C) 2019 Trent Piepho + * + * helper functions when coping with rational numbers + */ + +#include +#include +#include +#include +#include +#include + +/* + * calculate best rational approximation for a given fraction + * taking into account restricted register size, e.g. to find + * appropriate values for a pll with 5 bit denominator and + * 8 bit numerator register fields, trying to set up with a + * frequency ratio of 3.1415, one would say: + * + * rational_best_approximation(31415, 10000, + * (1 << 8) - 1, (1 << 5) - 1, &n, &d); + * + * you may look at given_numerator as a fixed point number, + * with the fractional part size described in given_denominator. + * + * for theoretical background, see: + * https://en.wikipedia.org/wiki/Continued_fraction + */ + +void rational_best_approximation( + unsigned long given_numerator, unsigned long given_denominator, + unsigned long max_numerator, unsigned long max_denominator, + unsigned long *best_numerator, unsigned long *best_denominator) +{ + /* n/d is the starting rational, which is continually + * decreased each iteration using the Euclidean algorithm. + * + * dp is the value of d from the prior iteration. + * + * n2/d2, n1/d1, and n0/d0 are our successively more accurate + * approximations of the rational. They are, respectively, + * the current, previous, and two prior iterations of it. + * + * a is current term of the continued fraction. + */ + unsigned long n, d, n0, d0, n1, d1, n2, d2; + n = given_numerator; + d = given_denominator; + n0 = d1 = 0; + n1 = d0 = 1; + + for (;;) { + unsigned long dp, a; + + if (d == 0) + break; + /* Find next term in continued fraction, 'a', via + * Euclidean algorithm. + */ + dp = d; + a = n / d; + d = n % d; + n = dp; + + /* Calculate the current rational approximation (aka + * convergent), n2/d2, using the term just found and + * the two prior approximations. + */ + n2 = n0 + a * n1; + d2 = d0 + a * d1; + + /* If the current convergent exceeds the maxes, then + * return either the previous convergent or the + * largest semi-convergent, the final term of which is + * found below as 't'. + */ + if ((n2 > max_numerator) || (d2 > max_denominator)) { + unsigned long t = ULONG_MAX; + + if (d1) + t = (max_denominator - d0) / d1; + if (n1) + t = min(t, (max_numerator - n0) / n1); + + /* This tests if the semi-convergent is closer than the previous + * convergent. If d1 is zero there is no previous convergent as this + * is the 1st iteration, so always choose the semi-convergent. + */ + if (!d1 || 2u * t > a || (2u * t == a && d0 * dp > d1 * d)) { + n1 = n0 + t * n1; + d1 = d0 + t * d1; + } + break; + } + n0 = n1; + n1 = n2; + d0 = d1; + d1 = d2; + } + *best_numerator = n1; + *best_denominator = d1; +} + +EXPORT_SYMBOL(rational_best_approximation); + +MODULE_DESCRIPTION("Rational fraction support library"); +MODULE_LICENSE("GPL v2"); -- cgit v1.3.1