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# Implementation of `Intrinsic` types in f18
```{contents}
---
local:
---
```
Intrinsic types are integer, real, complex, character, and logical.
All intrinsic types have a kind type parameter called KIND,
which determines the representation method for the specified type.
The intrinsic type character also has a length type parameter called LEN,
which determines the length of the character string.
The implementation of `CHARACTER` type in f18 is described
in [Character.md](Character.md).
## Supported TYPES and KINDS
Here are the type and kind combinations supported in f18:
INTEGER(KIND=1) 8-bit two's-complement integer
INTEGER(KIND=2) 16-bit two's-complement integer
INTEGER(KIND=4) 32-bit two's-complement integer
INTEGER(KIND=8) 64-bit two's-complement integer
INTEGER(KIND=16) 128-bit two's-complement integer
REAL(KIND=2) 16-bit IEEE 754 binary16 (5e11m)
REAL(KIND=3) 16-bit upper half of 32-bit IEEE 754 binary32 (8e8m)
REAL(KIND=4) 32-bit IEEE 754 binary32 (8e24m)
REAL(KIND=8) 64-bit IEEE 754 binary64 (11e53m)
REAL(KIND=10) 80-bit extended precision with explicit normalization bit (15e64m)
REAL(KIND=16) 128-bit IEEE 754 binary128 (15e113m)
COMPLEX(KIND=2) Two 16-bit IEEE 754 binary16
COMPLEX(KIND=3) Two 16-bit upper half of 32-bit IEEE 754 binary32
COMPLEX(KIND=4) Two 32-bit IEEE 754 binary32
COMPLEX(KIND=8) Two 64-bit IEEE 754 binary64
COMPLEX(KIND=10) Two 80-bit extended precisions values
COMPLEX(KIND=16) Two 128-bit IEEE 754 binary128
No
[double-double
](https://en.wikipedia.org/wiki/Quadruple-precision_floating-point_format)
quad precision type is supported.
LOGICAL(KIND=1) 8-bit integer
LOGICAL(KIND=2) 16-bit integer
LOGICAL(KIND=4) 32-bit integer
LOGICAL(KIND=8) 64-bit integer
No 128-bit logical support.
### Defaults kinds
INTEGER 4
REAL 4
COMPLEX 4
DOUBLE PRECISION 8
LOGICAL 4
#### Modifying the default kind with default-real-8.
REAL 8
DOUBLE PRECISION 8
COMPLEX 8
#### Modifying the default kind with default-integer-8:
INTEGER 8
LOGICAL 8
Modules compiled with different default-real and default-integer kinds
may be freely mixed.
Module files encode the kind value for every entity.
## Representation of LOGICAL variables
The default logical is `LOGICAL(KIND=4)`.
Logical literal constants with kind 1, 2, 4, and 8
share the following characteristics:
.TRUE. is represented as 1_kind
.FALSE. is represented as 0_kind
Tests for true is *integer value is not zero*.
The implementation matches gfortran.
Programs should not use integer values in LOGICAL contexts or
use LOGICAL values to interface with other languages.
### Representations of LOGICAL variables in other compilers
#### Intel ifort / NVIDA nvfortran / PGI pgf90
.TRUE. is represented as -1_kind
.FALSE. is represented as 0_kind
Any other values result in undefined behavior.
Values with a low-bit set are treated as .TRUE..
Values with a low-bit clear are treated as .FALSE..
#### IBM XLF
.TRUE. is represented as 1_kind
.FALSE. is represented as 0_kind
Values with a low-bit set are treated as .TRUE..
Values with a low-bit clear are treated as .FALSE..
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