Chapter 2 C Language Reference
AutoCode Reference 2-28 ni.com
language and replace the supplied macros (or functions) with your
(assembly) functions so that you can take full advantage of the processor’s
arithmetic capabilities.
Generated Code with Fixed-Point Variables
Code generated for models using fixed-point variables—such as the
examples provided in this chapter—will differ from code generated for
models using floating-point, integer, or logical signals in the following
areas:
• Signal and variable type declarations will reflect fixed-point types.
• Arithmetic operators +, –, *, and / will be replaced by fixed-point
arithmetic macro calls (or function calls based on the interface used).
• Relational operators >, >=, <, <=, ==, and != will, when necessary, be
replaced by fixed-point relational macro calls.
• Floating-point literals used in SystemBuild models will be replaced by
the scaled integer counterpart.
• Macros (or procedures) for converting between various fixed-point
types will be invoked when necessary.
Fixed-Point Data Types
Fixed-point type definitions are provided in the system-specific files src
directory. Files sa_types.h, sa_defn.h, sa_fxscale.h, and
sa_fxlimit.h use typedef statements to represent fixed-point types
and related constants for 8-bit, 16-bit, and 32-bit data. All fixed-point types
have an associated radix position value and a sign (signed or unsigned).
The radix position value is clearly related to the data type scale factor
scale factor = 2–(radix position). To perform any arithmetic operation, both the
value and the radix position scalar are required. The table below lists the
data types generated by AutoCode/C. For information on ranges and
accuracy of each type, refer to the SystemBuild User Guide.
Table 2-6. AutoCode/C Data Types
Data
Type
Number
of Bits
Signed or
Unsigned Data Type Name
byte 8unsigned RT_UBYTE (radix 00)
RT_UBYTExx (xx = radix 48 to –16)
signed RT_SBYTE (radix 00)
RT_SBYTExx (xx = radix 48 to –16)