PENF

February 27, 2026 · View on GitHub

Portability Environment for Fortran Poor People

A KISS pure Fortran 2003+ library for portable, parametrized numerical types — kind parameters, format strings, number ↔ string conversions, and more.

🔢 Kind Parameters Integers `I1P`–`I8P` and reals `R4P`/`R8P`/`R16P`, portable across compilers	🔄 Number ↔ String `str()`, `strz()`, `cton()`, `bstr()`, `bcton()` — full round-trips	📐 Format Strings & Limits Ready-made `FIP` / `FRP` formats and min/max values for every kind	📏 Bit & Byte Sizes `bit_size()` / `byte_size()` extended to reals, integers, and characters
⚡ Pure Fortran 2003+ No C, no external deps — tested with gfortran ≥ 4.9.2 and ifort ≥ 12.x	🔓 Multi-licensed GPL v3 · BSD 2/3-Clause · MIT	📦 Multiple build systems fpm, FoBiS.py, CMake, Makefile	📖 Documented & Tested API reference + doctests for all type variants

For full documentation (guide, API reference, examples, etc.) see the PENF website.

Authors

Stefano Zaghi — @szaghi

Contributions are welcome — see the Contributing page.

Copyrights

This project is distributed under a multi-licensing system:

FOSS projects: GPL v3
Closed source / commercial: BSD 2-Clause, BSD 3-Clause, or MIT

Anyone interested in using, developing, or contributing to this project is welcome — pick the license that best fits your needs.

Quick start

use penf
call penf_init

real(R8P)    :: x = -1.0_R8P
integer(I4P) :: n = 42_I4P

print FR8P, x !  -0.100000000000000E+001
print FI4P, n !          42

Real kinds

Parameter	Precision	Range	Size
`R16P`	33 digits	$[10^{-4931},\ 10^{+4931}-1]$	128 bit
`R8P`	15 digits	$[10^{-307},\ 10^{+307}-1]$	64 bit
`R4P`	6 digits	$[10^{-37},\ 10^{+37}-1]$	32 bit

Integer kinds

Parameter	Range	Size
`I8P`	$[-2^{63},\ +2^{63}-1]$	64 bit
`I4P`	$[-2^{31},\ +2^{31}-1]$	32 bit
`I2P`	$[-2^{15},\ +2^{15}-1]$	16 bit
`I1P`	$[-2^{7},\ +2^{7}-1]$	8 bit

Format Strings

Each kind has a matching format string for print / write statements:

Kind	Format string	Example output
`R16P`	`FR16P = '(E42.33E4)'`	`-0.100000000000000000000000000000000E+0001`
`R8P`	`FR8P = '(E23.15E3)'`	`-0.100000000000000E+001`
`R4P`	`FR4P = '(E13.6E2)'`	`-0.100000E+01`
`I8P`	`FI8P = '(I20)'`	`-1`
`I4P`	`FI4P = '(I11)'`	`-1`
`I2P`	`FI2P = '(I6)'`	`-1`
`I1P`	`FI1P = '(I4)'`	`-1`

Install

FoBiS.py

Standalone — clone, build, and install in one command:

FoBiS.py install szaghi/PENF -mode static-gnu
FoBiS.py install szaghi/PENF -mode static-gnu --prefix /path/to/prefix

As a project dependency — declare PENF in your fobos and run fetch:

[dependencies]
deps_dir = src/third_party
PENF     = https://github.com/szaghi/PENF

FoBiS.py fetch           # fetch and build
FoBiS.py fetch --update  # re-fetch and rebuild

fpm

Add to your fpm.toml:

[dependencies]
PENF = { git = "https://github.com/szaghi/PENF" }

CMake

cmake -B build && cmake --build build

Makefile

make              # static library
make TESTS=yes    # build and run tests