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 are short _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 _Fract and _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 _Accum and _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.