fortran-II-examples

Fortran II (year 1958) examples from IBM 704 Fortran II manual with modern Fortran equivalents.

The benchmark shows that good modern Fortran coding can be orders of magnitude faster than Fortran 77 techniques.

Requirements

Most Fortran compilers can handle the Fortran II code within. Of course there will be some compiler warnings.

Build / Usage

make

./bench

Benchmark

An arctan function is tested.

• Intrinsic: Fortran built-in atan()
• New: My implementatin in modern Fortran of the 1958 IBM arctangent function
• Old: Fortran 77 implementation of 1958 IBM arctangent function

time in seconds. Optimization -O3

Flang 5.0 make FC=flang

./bench 1000000
intrinsic     1.740E-02  modern Fortran     6.861E-02  Fortran 77      6.119E-02

./bench 10000000
intrinsic     1.397E-01  modern Fortran     6.690E-01  Fortran 77      6.231E-01

Intel Fortran 2019 make FC=ifort

./bench 1000000
intrinsic     2.648E-03  modern Fortran     9.605E-02  Fortran 77      8.485E-02

./bench 10000000
intrinsic     2.596E-02  modern Fortran     9.397E-01  Fortran 77      8.574E-01

PGI 2017 make FC=pgf95

 ./bench 1000000
intrinsic     5.782E-03  modern Fortran     6.846E-02  Fortran 77      6.339E-02

./bench 10000000
intrinsic     3.290E-02  modern Fortran     7.069E-01  Fortran 77      6.356E-01

Using the same algorithm, modern Fortran 95+ techniques are approximately the same speed as awkward Fortran 77 style coding.

Notes

Subprograms/program units (now known as "procedures" e.g. functions and subroutines) must be concluded for Fortran II (1958) with

RETURN
END

However, since Fortran 66, all that's needed for ending procedures (functions and subroutines) is

END

so there's no need to be anachronistic--just end with end subroutine or end function

• Fortran II (1958) manual
• Fortran 66 standard
• Fortran 77 langauge reference

Function statements

The original 1957 Fortran had "statement functions", which in 1957 Fortran and Fortran II were required to have a name ending in F e.g. MINIMAXF.