Fixed-Point (Using the GNU Compiler Collection (GCC)) (original) (raw)

6.1.7 Fixed-Point Types ¶

As an extension, GNU C supports fixed-point types as defined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-point types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support fixed-point types.

The fixed-point types areshort _Fract,_Fract,long _Fract,long long _Fract,unsigned short _Fract,unsigned _Fract,unsigned long _Fract,unsigned long long _Fract,_Sat short _Fract,_Sat _Fract,_Sat long _Fract,_Sat long long _Fract,_Sat unsigned short _Fract,_Sat unsigned _Fract,_Sat unsigned long _Fract,_Sat unsigned long long _Fract,short _Accum,_Accum,long _Accum,long long _Accum,unsigned short _Accum,unsigned _Accum,unsigned long _Accum,unsigned long long _Accum,_Sat short _Accum,_Sat _Accum,_Sat long _Accum,_Sat long long _Accum,_Sat unsigned short _Accum,_Sat unsigned _Accum,_Sat unsigned long _Accum,_Sat unsigned long long _Accum.

Fixed-point data values contain fractional and optional integral parts. The format of fixed-point data varies and depends on the target machine.

Support for fixed-point types includes:

• prefix and postfix increment and decrement operators (++, --)
• unary arithmetic operators (+, -, !)
• binary arithmetic operators (+, -, *, /)
• binary shift operators (<<, >>)
• relational operators (<, <=, >=, >)
• equality operators (==, !=)
• assignment operators (+=, -=, *=, /=,<<=, >>=)
• conversions to and from integer, floating-point, or fixed-point types

Use a suffix in a fixed-point literal constant:

• ‘hr’ or ‘HR’ for short _Fract and_Sat short _Fract
• ‘r’ or ‘R’ for _Fract and _Sat _Fract
• ‘lr’ or ‘LR’ for long _Fract and_Sat long _Fract
• ‘llr’ or ‘LLR’ for long long _Fract and_Sat long long _Fract
• ‘uhr’ or ‘UHR’ for unsigned short _Fract and_Sat unsigned short _Fract
• ‘ur’ or ‘UR’ for unsigned _Fract and_Sat unsigned _Fract
• ‘ulr’ or ‘ULR’ for unsigned long _Fract and_Sat unsigned long _Fract
• ‘ullr’ or ‘ULLR’ for unsigned long long _Fractand _Sat unsigned long long _Fract
• ‘hk’ or ‘HK’ for short _Accum and_Sat short _Accum
• ‘k’ or ‘K’ for _Accum and _Sat _Accum
• ‘lk’ or ‘LK’ for long _Accum and_Sat long _Accum
• ‘llk’ or ‘LLK’ for long long _Accum and_Sat long long _Accum
• ‘uhk’ or ‘UHK’ for unsigned short _Accum and_Sat unsigned short _Accum
• ‘uk’ or ‘UK’ for unsigned _Accum and_Sat unsigned _Accum
• ‘ulk’ or ‘ULK’ for unsigned long _Accum and_Sat unsigned long _Accum
• ‘ullk’ or ‘ULLK’ for unsigned long long _Accumand _Sat unsigned long long _Accum

GCC support of fixed-point types as specified by the draft technical report is incomplete:

• Pragmas to control overflow and rounding behaviors are not implemented.

Fixed-point types are supported by the DWARF debug information format.