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8
9# Implementation of `Intrinsic` types in f18
10
11```eval_rst
12.. contents::
13   :local:
14```
15
16Intrinsic types are integer, real, complex, character, and logical.
17All intrinsic types have a kind type parameter called KIND,
18which determines the representation method for the specified type.
19The intrinsic type character also has a length type parameter called LEN,
20which determines the length of the character string.
21
22The implementation of `CHARACTER` type in f18 is described
23in [Character.md](Character.md).
24
25## Supported TYPES and KINDS
26
27Here are the type and kind combinations supported in f18:
28
29INTEGER(KIND=1) 8-bit two's-complement integer
30INTEGER(KIND=2) 16-bit two's-complement integer
31INTEGER(KIND=4) 32-bit two's-complement integer
32INTEGER(KIND=8) 64-bit two's-complement integer
33INTEGER(KIND=16) 128-bit two's-complement integer
34
35REAL(KIND=2) 16-bit IEEE 754 binary16 (5e11m)
36REAL(KIND=3) 16-bit upper half of 32-bit IEEE 754 binary32 (8e8m)
37REAL(KIND=4) 32-bit IEEE 754 binary32 (8e24m)
38REAL(KIND=8) 64-bit IEEE 754 binary64 (11e53m)
39REAL(KIND=10) 80-bit extended precision with explicit normalization bit (15e64m)
40REAL(KIND=16) 128-bit IEEE 754 binary128 (15e113m)
41
42COMPLEX(KIND=2) Two 16-bit IEEE 754 binary16
43COMPLEX(KIND=3) Two 16-bit upper half of 32-bit IEEE 754 binary32
44COMPLEX(KIND=4) Two 32-bit IEEE 754 binary32
45COMPLEX(KIND=8) Two 64-bit IEEE 754 binary64
46COMPLEX(KIND=10) Two 80-bit extended precisions values
47COMPLEX(KIND=16) Two 128-bit IEEE 754 binary128
48
49No
50[double-double
51](https://en.wikipedia.org/wiki/Quadruple-precision_floating-point_format)
52quad precision type is supported.
53
54LOGICAL(KIND=1) 8-bit integer
55LOGICAL(KIND=2) 16-bit integer
56LOGICAL(KIND=4) 32-bit integer
57LOGICAL(KIND=8) 64-bit integer
58
59No 128-bit logical support.
60
61### Defaults kinds
62
63INTEGER 4
64REAL 4
65COMPLEX 4
66DOUBLE PRECISION 8
67LOGICAL 4
68
69#### Modifying the default kind with default-real-8.
70REAL 8
71DOUBLE PRECISION  8
72COMPLEX 8
73
74#### Modifying the default kind with default-integer-8:
75INTEGER 8
76
77There is no option to modify the default logical kind.
78
79Modules compiled with different default-real and default-integer kinds
80may be freely mixed.
81Module files encode the kind value for every entity.
82
83## Representation of LOGICAL variables
84
85The default logical is `LOGICAL(KIND=4)`.
86
87Logical literal constants with kind 1, 2, 4, and 8
88share the following characteristics:
89.TRUE. is represented as 1_kind
90.FALSE. is represented as 0_kind
91
92Tests for true is *integer value is not zero*.
93
94The implementation matches gfortran.
95
96Programs should not use integer values in LOGICAL contexts or
97use LOGICAL values to interface with other languages.
98
99### Representations of LOGICAL variables in other compilers
100
101##### Intel ifort / NVIDA nvfortran / PGI pgf90
102.TRUE. is represented as -1_kind
103.FALSE. is represented as 0_kind
104Any other values result in undefined behavior.
105
106Values with a low-bit set are treated as .TRUE..
107Values with a low-bit clear are treated as .FALSE..
108
109##### IBM XLF
110.TRUE. is represented as 1_kind
111.FALSE. is represented as 0_kind
112
113Values with a low-bit set are treated as .TRUE..
114Values with a low-bit clear are treated as .FALSE..
115