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+/**
+ * Copyright © 2014  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef ALGO_ALGORITHMS_BITS_ABSOLUTE_H
+#define ALGO_ALGORITHMS_BITS_ABSOLUTE_H
+
+
+/* NB! This will not play nice if the placeholder `T` is
+ * not set to a type only containing [0-9A-Za-z_] (and $
+ * in GNU C). Therefore, with the exception of `char`,
+ * `short`, `int`, `long`, `float` and `double`, you
+ * should only use `typedef`:ed types. */
+
+
+#include <limits.h>
+
+
+/* Note: This file is purely academical, your compiler should
+ * be able to select the fast way to compute the absolute value
+ * if you write `(a > 0 ? a : -a)`, in GNU C:
+ * 
+ *     ({
+ *         typeof(a) a_ = a;
+ *         a_ > 0 ? a : -a;
+ *     })
+ * 
+ * GCC also have built in functions like `__builtin_labs`
+ * for calculating the the absolute value of a value.
+ */
+
+
+/**
+ * Compute the absolute value of an integer.
+ * 
+ * This function only works on integer types. And it
+ * assumes that two's complement is used, which is
+ * always true if you use GCC and is true for most
+ * (all?) high-level programming languages.
+ * 
+ * `algo_make_implementation_of_abs_twos_complement(T)`
+ * is used to make this function available for a particular
+ * data type `T`. And implementation without modifiers and
+ * attributes will be expanded. You may add `static`,
+ * `inline` and `__attribute__` before calling
+ * `algo_make_implementation_of_abs_twos_complement(T)`.
+ * 
+ * `algo_make_prototype_of_abs_twos_complement(T)`
+ * is the prototype counterpart of
+ * `algo_make_implementation_of_abs_twos_complement(T)`.
+ * It too is will not add any modifiers or attributes by
+ * default. It will neither add a semicolon at the end of
+ * the prototype.
+ * 
+ * `algo_abs_twos_complement(T)` is used to get the version
+ * of the function that supports the data type `T`.
+ * `&(algo_abs_twos_complement(T))` gets the address of this
+ * function and `algo_abs_twos_complement(T)(items, n, min, max)`
+ * calls the function.
+ * 
+ * This function is constant, if you are using GCC you
+ * should add `__attribute__((const))` to its prototype.
+ * 
+ * @param   value  The value whose absolute value should be calculated.
+ * @return         The absolute value of `value`. If `value` is its
+ *                 minimum possible value, `value` will be returned
+ *                 verbatim because of overflow.
+ */
+//>fun () {
+T algo_abs_twos_complement__##T(T value)
+{
+  /* Compiles to three operations. */
+  T mask = value >> (sizeof(T) * CHAR_BIT - 1);
+  return (value ^ mask) - mask;
+  /* Or alternatively: (value + mask) ^ mask */
+}
+//>} ; . ../make_fun
+
+
+/**
+ * Compute the absolute value of an integer.
+ * 
+ * This function only works on integer types. And it
+ * assumes that ones' complement is used, which is
+ * seldom true and is always false if you use GCC.
+ * 
+ * `algo_make_implementation_of_abs_ones_complement(T)`
+ * is used to make this function available for a particular
+ * data type `T`. And implementation without modifiers and
+ * attributes will be expanded. You may add `static`,
+ * `inline` and `__attribute__` before calling
+ * `algo_make_implementation_of_abs_ones_complement(T)`.
+ * 
+ * `algo_make_prototype_of_abs_ones_complement(T)`
+ * is the prototype counterpart of
+ * `algo_make_implementation_of_abs_ones_complement(T)`.
+ * It too is will not add any modifiers or attributes by
+ * default. It will neither add a semicolon at the end of
+ * the prototype.
+ * 
+ * `algo_abs_ones_complement(T)` is used to get the version
+ * of the function that supports the data type `T`.
+ * `&(algo_abs_ones_complement(T))` gets the address of this
+ * function and `algo_abs_ones_complement(T)(items, n, min, max)`
+ * calls the function.
+ * 
+ * This function is constant, if you are using GCC you
+ * should add `__attribute__((const))` to its prototype.
+ * 
+ * @param   value  The value whose absolute value should be calculated.
+ * @return         The absolute value of `value`.
+ */
+//>fun () {
+T algo_abs_ones_complement__##T(T value)
+{
+  /* Compiles to two operations. */
+  T mask = value >> (sizeof(T) * CHAR_BIT - 1);
+  return value ^ mask;
+}
+//>} ; . ../make_fun
+
+
+/**
+ * Compute the absolute value of an integer.
+ * 
+ * This function only works on integer types. And it
+ * assumes that sign–magnitude is used, which is
+ * seldom true and is always false if you use GCC.
+ * 
+ * `algo_make_implementation_of_abs_sign_magnitude(T)`
+ * is used to make this function available for a particular
+ * data type `T`. And implementation without modifiers and
+ * attributes will be expanded. You may add `static`,
+ * `inline` and `__attribute__` before calling
+ * `algo_make_implementation_of_abs_sign_magnitude(T)`.
+ * 
+ * `algo_make_prototype_of_abs_sign_magnitude(T)`
+ * is the prototype counterpart of
+ * `algo_make_implementation_of_abs_sign_magnitude(T)`.
+ * It too is will not add any modifiers or attributes by
+ * default. It will neither add a semicolon at the end of
+ * the prototype.
+ * 
+ * `algo_abs_sign_magnitude(T)` is used to get the version
+ * of the function that supports the data type `T`.
+ * `&(algo_abs_sign_magnitude(T))` gets the address of this
+ * function and `algo_abs_sign_magnitude(T)(items, n, min, max)`
+ * calls the function.
+ * 
+ * This function is constant, if you are using GCC you
+ * should add `__attribute__((const))` to its prototype.
+ * 
+ * @param   value  The value whose absolute value should be calculated.
+ * @return         The absolute value of `value`.
+ */
+//>fun () {
+T algo_abs_sign_magnitude__##T(T value)
+{
+  /* Compiles to one operation. */
+  const T magnitude = ~(1 ^ -1);
+  return value & magnitude;
+  /* Or alternatively: magnitude = ~(1 << (sizeof(T) * CHAR_BIT - 1)) */
+}
+//>} ; . ../make_fun
+
+
+#endif
+