Using the GNU Compiler Collection (GCC): Fixed-Point

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### 6.15 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.

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