If the -funsigned option is given, GNU Fortran supports unsigned integers according to J3/24-116. The data type is called UNSIGNED. For an unsigned type with n bits, it implements integer arithmetic modulo 2**n, comparable to the unsigned data type in C.
The data type has KIND numbers comparable to other Fortran data types, which can be selected via the SELECTED_UNSIGNED_KIND function.
Mixed arithmetic, comparisons and assignment between UNSIGNED and other types are only possible via explicit conversion. Conversion from UNSIGNED to other types is done via type conversion functions like INT or REAL. Conversion from other types to UNSIGNED is done via UINT. Unsigned variables cannot be used as index variables in DO loops or as array indices.
Unsigned numbers have a trailing u as suffix, optionally followed by a KIND number separated by an underscore.
Input and output can be done using the ‘I’, ‘B’, ‘O’ and ‘Z’ descriptors, plus unformatted I/O.
Here is a small, somewhat contrived example of their use:
program main use iso_fortran_env, only : uint64 unsigned(kind=uint64) :: v v = huge(v) - 32u_uint64 print *,v end program main
which outputs the number 18446744073709551583.
Arithmetic operations work on unsigned integers, also for exponentiation. As an extension to J3/24-116.txt, unary minus and exponentiation of unsigned integers are permitted unless -pedantic is in force.
In intrinsic procedures, unsigned arguments are typically permitted for arguments for the data to be processed, analogous to the use of REAL arguments. Unsigned values are prohibited as index variables in DO loops and as array indices.
Unsigned numbers can be read and written using list-directed, formatted and unformatted I/O. For formatted I/O, the ‘B’, ‘I’, ‘O’ and ‘Z’ descriptors are valid. Negative values and values that would overflow are rejected with -pedantic.
SELECT CASE is supported for unsigned integers.
The following intrinsics take unsigned arguments:
BGE, see BGE — Bitwise greater than or equal to BGT, see BGT — Bitwise greater than BIT_SIZE, see BIT_SIZE — Bit size inquiry function BLE, see BLE — Bitwise less than or equal to BLT, see BLT — Bitwise less than CMPLX, see CMPLX — Complex conversion function CSHIFT, see CSHIFT — Circular shift elements of an array DIGITS, see DIGITS — Significant binary digits function DOT_PRODUCT, see DOT_PRODUCT — Dot product function DSHIFTL, see DSHIFTL — Combined left shift DSHIFTR, see DSHIFTR — Combined right shift EOSHIFT, see EOSHIFT — End-off shift elements of an array FINDLOC, see FINDLOC — Search an array for a value HUGE, see HUGE — Largest number of a kind IALL, see IALL — Bitwise AND of array elements IAND, see IAND — Bitwise logical and IANY, see IANY — Bitwise OR of array elements IBCLR, see IBCLR — Clear bit IBITS, see IBITS — Bit extraction IBSET, see IBSET — Set bit IEOR, see IEOR — Bitwise logical exclusive or INT, see INT — Convert to integer type IOR, see IOR — Bitwise logical or IPARITY, see IPARITY — Bitwise XOR of array elements ISHFT, see ISHFT — Shift bits ISHFTC, see ISHFTC — Shift bits circularly MATMUL, see MATMUL — matrix multiplication MAX, see MAX — Maximum value of an argument list MAXLOC, see MAXLOC — Location of the maximum value within an array MAXVAL, see MAXVAL — Maximum value of an array MERGE, see MERGE — Merge variables MERGE_BITS, see MERGE_BITS — Merge of bits under mask MIN, see MIN — Minimum value of an argument list MINLOC, see MINLOC — Location of the minimum value within an array MINVAL, see MINVAL — Minimum value of an array MOD, see MOD — Remainder function MODULO, see MODULO — Modulo function MVBITS, see MVBITS — Move bits from one integer to another NOT, see NOT — Logical negation OUT_OF_RANGE, see OUT_OF_RANGE — Range check for numerical conversion PRODUCT, see PRODUCT — Product of array elements RANDOM_NUMBER, see RANDOM_NUMBER — Pseudo-random number RANGE, see RANGE — Decimal exponent range REAL, see REAL — Convert to real type SHIFTA, see SHIFTA — Right shift with fill SHIFTL, see SHIFTL — Left shift SHIFTR, see SHIFTR — Right shift SUM, see SUM — Sum of array elements TRANSPOSE, see TRANSPOSE — Transpose an array of rank two TRANSFER, see TRANSFER — Transfer bit patterns The following intrinsics are enabled with -funsigned:
UINT, see UINT – Convert to UNSIGNED type UMASKL, see UMASKL — Unsigned left justified mask UMASKR, see UMASKR — Unsigned right justified mask SELECTED_UNSIGNED_KIND, see SELECTED_UNSIGNED_KIND — Choose unsigned kind The following constants have been added to the intrinsic ISO_C_BINDING module: c_unsigned, c_unsigned_short, c_unsigned_char, c_unsigned_long, c_unsigned_long_long, c_uintmax_t, c_uint8_t, c_uint16_t, c_uint32_t, c_uint64_t, c_uint128_t, c_uint_fast8_t, c_uint_fast16_t, c_uint_fast32_t, c_uint_fast64_t, c_uint_fast128_t, c_uint_least8_t, c_uint_least16_t, c_uint_least32_t, c_uint_least64_t and c_uint_least128_t.
The following constants have been added to the intrinsic ISO_FORTRAN_ENV module: uint8, uint16, uint32 and uint64.