6.1.22 Type variants for integer intrinsics

Similar to the D/C prefixes to real functions to specify the input/output types, GNU Fortran offers B/I/J/K prefixes to integer functions for compatibility with DEC programs. The types implied by each are:

B - INTEGER(kind=1)
I - INTEGER(kind=2)
J - INTEGER(kind=4)
K - INTEGER(kind=8)

GNU Fortran supports these with the flag -fdec-intrinsic-ints. Intrinsics for which prefixed versions are available and in what form are noted in Intrinsic Procedures. The complete list of supported intrinsics is here:

Intrinsic	B	I	J	K
`ABS`	`BABS`	`IIABS`	`JIABS`	`KIABS`
`BTEST`	`BBTEST`	`BITEST`	`BJTEST`	`BKTEST`
`IAND`	`BIAND`	`IIAND`	`JIAND`	`KIAND`
`IBCLR`	`BBCLR`	`IIBCLR`	`JIBCLR`	`KIBCLR`
`IBITS`	`BBITS`	`IIBITS`	`JIBITS`	`KIBITS`
`IBSET`	`BBSET`	`IIBSET`	`JIBSET`	`KIBSET`
`IEOR`	`BIEOR`	`IIEOR`	`JIEOR`	`KIEOR`
`IOR`	`BIOR`	`IIOR`	`JIOR`	`KIOR`
`ISHFT`	`BSHFT`	`IISHFT`	`JISHFT`	`KISHFT`
`ISHFTC`	`BSHFTC`	`IISHFTC`	`JISHFTC`	`KISHFTC`
`MOD`	`BMOD`	`IMOD`	`JMOD`	`KMOD`
`NOT`	`BNOT`	`INOT`	`JNOT`	`KNOT`
`REAL`	`--`	`FLOATI`	`FLOATJ`	`FLOATK`

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https://gcc.gnu.org/onlinedocs/gcc-9.3.0/gfortran/Type-variants-for-integer-intrinsics.html