MPLAB C Compiler for PIC24 MCUs and dsPIC DSCs ... - Microchip

Differences Between 16-Bit Device C and ANSI C
2.3.5 Complex Numbers
The compiler supports complex data types. You can declare both complex integer
types and complex floating types, using the keyword __complex__.
For example, __complex__ float x; declares x as a variable whose real part and
imaginary part are both of type float. __complex__ short int y; declares y to
have real and imaginary parts of type short int.
To write a constant with a complex data type, use the suffix ‘i’ or ‘j’ (either one; they
are equivalent). For example, 2.5fi has type __complex__ float and 3i has type
__complex__ int. Such a constant is a purely imaginary value, but you can form
any complex value you like by adding one to a real constant.
To extract the real part of a complex-valued expression exp, write __real__ exp.
Similarly, use __imag__ to extract the imaginary part. For example;
__complex__ float z;
float r;
float i;
r = __real__ z;
i = __imag__ z;
The operator ‘~’ performs complex conjugation when used on a value with a complex
type.
The compiler can allocate complex automatic variables in a noncontiguous fashion; it’s
even possible for the real part to be in a register while the imaginary part is on the stack
(or vice-versa). The debugging information format has no way to represent noncontiguous
allocations like these, so the compiler describes noncontiguous complex
variables as two separate variables of noncomplex type. If the variable’s actual name
is foo, the two fictitious variables are named foo$real and foo$imag.
2.3.6 Double-Word Integers
The compiler supports data types for integers that are twice as long as long int.
Simply write long long int for a signed integer, or unsigned long long int
for an unsigned integer. To make an integer constant of type long long int, add the
suffix LL to the integer. To make an integer constant of type unsigned long long
int, add the suffix ULL to the integer.
You can use these types in arithmetic like any other integer types. Addition, subtraction
and bitwise boolean operations on these types are open-coded, but division and shifts
are not open-coded. The operations that are not open-coded use special library
routines that come with the compiler.
2.3.7 Referring to a Type with typeof
Another way to refer to the type of an expression is with the typeof keyword. The
syntax for using this keyword looks like sizeof, but the construct acts semantically like
a type name defined with typedef.
There are two ways of writing the argument to typeof: with an expression or with a
type. Here is an example with an expression:
typeof (x[0](1))
This assumes that x is an array of functions; the type described is that of the values of
the functions.
Here is an example with a typename as the argument:
typeof (int *)
© 2008 Microchip Technology Inc. DS51284H-page 29