lapack

Indentation by steps of 3 spaces is common in old Fortran 77 code. This is LAPACK for example. Scroll down to about line 400 to see actual code, not comments. https://github.com/Reference-LAPACK/lapack/blob/master/SRC/c...

https://github.com/Reference-LAPACK/lapack/commits/master said fortran code happily gets minor and major updates

I have not kept up with recent developments, but Fortran has historically been noticeably faster than even C/C++ for numerical computations. This difference used to be quite stark due to limitations in C itself: http://www.ibiblio.org/pub/languages/fortran/ch1-2.html (see " b) The design of FORTRAN allows maximal speed of execution:") I think things have gotten better in C, e.g. with C99's "restrict" keyword, along with general improvements in C compilers, but for a long while Fortran had a clear upper hand when it came to allocating and manipulating large arrays of floats. Outside of the language specification, I would wager that many supercomputers have better-optimized Fortran compilers than C compilers for this reason. And even if in principle C and Fortran can execute equally performant numeric code, Fortran's historic superiority ha

The variable names are mostly from the paper, since the blog post mostly just transliterated the Pascal code in the appendix. Some of them are explained. n: sample size. N: file size / total record count. U,V: independent uniform variates. X: random variate approximating skip distance. S: skip distance. qu1: N-n+1. y1 and y2 aren't explained, they're just intermediate formulas. t seems to be a local loop variable. i and j are index variables for the array used to return the sample, introduced by the blogpost. I'm not saying it's good code, but BLAS is similar: https://github.com/Reference-LAPACK/lapack/blob/master/BLAS/.... At some point working code beats comprehensibility.