/**
* 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
