Specifications

CAVR-4
Part1. Using the compiler
Efficient coding for embedded applications
127
For details about representation of supported data types, pointers, and structures types,
see the chapter Data representation.
Floating-point types
Using floating-point types on a microprocessor without a math coprocessor is very
inefficient, both in terms of code size and execution speed. The AVR IAR C/C++
Compiler supports two floating-point formats—32 and 64 bits. The 32-bit floating-point
type
float is more efficient in terms of code size and execution speed. However, the
64-bit format double supports higher precision and larger numbers.
In the AVR IAR C/C++ Compiler, the floating-point type
float always uses the 32-bit
format. The format used by the double floating-point type depends on the compiler
option
--64bit_doubles (Use 64-bit doubles).
Unless the application requires the extra precision that 64-bit floating-point numbers
give, we recommend using 32-bit floats instead. Also consider replacing code using
floating-point operations with code using integers because these are more efficient.
Note that a floating-point constant in the source code is treated as being of the type
double. This can cause innocent-looking expressions to be evaluated in double
precision. In the example below
a is converted from a float to a double, 1 is added
and the result is converted back to a float:
float test(float a)
{
return a+1.0;
}
To treat a floating-point constant as a float rather than as a double, add an f to it, for
example:
float test(float a)
{
return a+1.0f;
}