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diff --git a/source/arduino/arithmetic.rst b/source/arduino/arithmetic.rst new file mode 100644 index 0000000..cbe3059 --- /dev/null +++ b/source/arduino/arithmetic.rst @@ -0,0 +1,104 @@ +.. highlight:: cpp + +.. _arduino-arithmetic: + +Addition, Subtraction, Multiplication, & Division +================================================= + +Description +----------- + +These operators return the sum, difference, product, or quotient +(respectively) of the two operands. The operation is conducted using +the data type of the operands, so, for example, ``9 / 4`` gives ``2`` +since 9 and 4 are ints. + +This also means that the operation can overflow if the result is +larger than that which can be stored in the data type (e.g. adding 1 +to an :ref:`arduino-int` with the value 2147483647 gives +-2147483648). If the operands are of different types, the "larger" +type is used for the calculation. + +(The specifics of these rules are beyond the scope of this +documentation; for more information, see `The C++ Programming Language +<http://www2.research.att.com/~bs/3rd.html>`_\ , by Bjarne +Stroustroup, Appendix C, especially §§C.4-C.6, or `this WikiBooks +entry on C++ type conversion +<http://en.wikibooks.org/wiki/C%2B%2B_Programming/Programming_Languages/C%2B%2B/Code/Statements/Variables/Type_Casting#Automatic_type_conversion>`_\ +. For more information on how computers represent integers, see the +Wikipedia page on `two's complement +<http://en.wikipedia.org/wiki/Two's_complement>`_\ ). + +If one of the numbers (operands) are of the type **float** or of type +**double**, floating point math will be used for the +calculation. + +Examples +-------- + + :: + + y = y + 3; + x = x - 7; + i = j * 6; + r = r / 5; + + +Syntax +------ + + :: + + result = value1 + value2; + result = value1 - value2; + result = value1 * value2; + result = value1 / value2; + + +Parameters: +----------- + +**value1**: any numeric variable or constant + +**value2**: any numeric variable or constant + + +Arduino Compatibility Note +-------------------------- + +Since the STM32 processor on the Maple is a 32-bit machine, the int +type overflows at a much higher value on Maple than on Arduino. In +particular, on Maple, ints do not overflow (become negative) until +they reach 2,147,483,648; on the Arduino, they overflow at 32,767. +Because of this, programs running on Maple are much less likely to run +into overflow issues. + + +Programming Tips: +----------------- + +- Know that :ref:`integer constants <arduino-integerconstants>` + default to :ref:`int <arduino-Int>`, so some constant calculations + may overflow (e.g., 200000 * 5000000 will yield a negative result). + +- Choose variable sizes that are large enough to hold the largest + results from your calculations. + +- Know at what point your variable will "roll over" and also what + happens in the other direction e.g. (0 - 1) for unsigned arithmetic, + or (0 - -2,147,483,648) for signed arithmetic. + +- For math that requires fractions, float variables may be used, but + be aware of their drawbacks: large size and slow computation speeds + (the STM32 has no floating point hardware, so all floating point + calculations have to be done in software). + +- Use the cast operator e.g. (int)myFloat to convert one variable type + to another on the fly. + + +See Also +-------- + +- `libmaple_types.h <http://github.com/leaflabs/libmaple/blob/master/libmaple/libmaple_types.h>`_ + |