#+TITLE: Programming Language Interstices
#+SUBTITLE: Bridging Fortran and Python
#+AUTHOR: Rohit Goswami
# I need the footnotes to be inlined
#+STARTUP: fninline
#+EXCLUDE_TAGS: noexport

#+BEGIN_SRC emacs-lisp :exports none :eval always
(require 'ox-extra)
(ox-extras-activate '(ignore-headlines))
(eval unpackaged/org-export-html-with-useful-ids-mode)
;; Stop using citeproc-org by default
(setq org-export-before-parsing-hook '(org-ref-acronyms-before-parsing org-ref-glossary-before-parsing org-attach-expand-links))
#+END_SRC

#+RESULTS:
| org-ref-acronyms-before-parsing | org-ref-glossary-before-parsing | org-attach-expand-links |


* Configuration :ignoreheading:ignore:
:PROPERTIES:
:VISIBILITY: folded
:END:

# Kanged from https://gitlab.com/oer/oer-reveal/blob/master/org/config.org
# Also https://gitlab.com/oer/emacs-reveal-howto/-/blob/master/howto.org
** General Options :ignoreheading:ignore:
# No Table of contents, no section numbers
#+OPTIONS: toc:nil num:nil

# Enable smart quotes
#+OPTIONS: ':t
** RevealJS Options :ignoreheading:ignore:

# Enable: browser history, fragment IDs in URLs, mouse wheel, links between presentations
#+OPTIONS: reveal_history:t reveal_fragmentinurl:t
#+OPTIONS: reveal_mousewheel:t reveal_inter_presentation_links:t

# Disable separate PDF pages for each fragment.  Just use one per slide.
#+OPTIONS: reveal_pdfseparatefragments:nil

# Display notes on separate page for PDF export.
#+REVEAL_EXPORT_NOTES_TO_PDF: separate-page

# Transition styles: none/fade/slide/convex/concave/zoom/cube
#+REVEAL_TRANS: fade
# Set a base theme, then override
#+REVEAL_THEME: robot-lung
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/extras/rlExtras.css
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/extras/oerFragments.css
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/extras/noImgBoxes.css
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/extras/betterCite.css
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/extras/moreCode.css
#+REVEAL_MARGIN: 0.2
#+REVEAL_PREAMBLE: <div class="line top"></div> <div class="line bottom"></div> <div class="line left"></div> <div class="line right"></div>

#+REVEAL_PLUGINS: (notes search zoom)
# The following variables are non-standard.
# Do not display TOC-progress on title slide.

#+REVEAL_TITLE_SLIDE_STATE: no-toc-progress
# Do not display TOC-progress on TOC slide.
#+REVEAL_TOC_SLIDE_STATE: no-toc-progress
# Do not include TOC slide in TOC-progress.
#+REVEAL_TOC_SLIDE_CLASS: no-toc-progress
# Use different heading for TOC.
#+REVEAL_TOC_SLIDE_TITLE: Agenda

** External Resources :ignoreheading:ignore:
# Note that doom-emacs sets this variable
# https://github.com/hlissner/doom-emacs/blob/develop/modules/lang/org/contrib/present.el
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/rjs/plugin/accessibility/helper.css
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/rjs/plugin/toc-progress/toc-progress.css
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/rjs/dist/theme/toc-style.css
#+REVEAL_EXTRA_CSS: /Users/rohitgoswami/.config/doom/reveal/rjs/dist/theme/fonts/source-sans-pro/source-sans-pro.css

# Allow to selectively hide links.
# #+REVEAL_EXTRA_SCRIPTS: ("/Users/rohitgoswami/.config/doom/reveal/rjs/dist/theme/hidelinks.js")
#+REVEAL_EXTRA_SCRIPTS: ("/Users/rohitgoswami/.config/doom/reveal/rjs/dist/theme/hidelinks.js" "/Users/rohitgoswami/.config/doom/reveal/sfeir-school-theme/dist/js/sfeir-theme.js")

# The following creates an empty footer, for which the css style defines
# a height that agrees with the TOC-progress footer’s height.
# In this way, the footer’s height is taken into account by reveal.js’s
# size calculations.
#+REVEAL_SLIDE_FOOTER: <br>
#+OPTIONS: reveal_toc_footer:t

** Macros :ignoreheading:ignore:
# Set a default bib file.

# Macros to display square brackets (in texts of hyperlinks).
# Based on: https://emacs.stackexchange.com/questions/7792/can-i-make-links-in-org-mode-that-contain-brackets-or
# Square Bracket Open [
#+MACRO: BO @@latex:\char91{}@@@@html:&#91;@@
# Square Bracket Close ]
#+MACRO: BC @@latex:\char93{}@@@@html:&#93;@@

# Macro for forced line break, e.g., in titles.
#+MACRO: BR @@latex:\\@@@@html:<br />@@

# Macro to generate abbr element in HTML.  If a second argument is given, it
# defines the title attribute.  For LaTeX, output first attribute as is and
# ignore second one.
#+MACRO: abbr (eval (concat "@@latex:" Modern Documentation across languages "@@@@html:<abbr" (if (< 0 (length Linguistic and Programmatic Variants)) (concat " title=\"" Linguistic and Programmatic Variants "\"") "") ">" Modern Documentation across languages "</abbr>@@"))

# Macros to display code in different colors.
#+MACRO: blackcode (eval (format "@@html:<code><span style=\"color:black; font-size:smaller;\">%s</span></code>@@ @@latex:\\verb|%s|@@" (org-html-encode-plain-text Modern Documentation across languages) Modern Documentation across languages))
#+MACRO: redcode (eval (format "@@html:<code><span style=\"color:darkred; font-size:smaller;\">%s</span></code>@@ @@latex:\\rverb|%s|@@" (org-html-encode-plain-text Modern Documentation across languages) Modern Documentation across languages))
#+MACRO: greencode (eval (format "@@html:<code><span style=\"color:darkgreen; font-size:smaller;\">%s</span></code>@@ @@latex:\\gverb|%s|@@" (org-html-encode-plain-text Modern Documentation across languages) Modern Documentation across languages))
#+MACRO: bluecode (eval (format "@@html:<code><span style=\"color:darkblue; font-size:smaller;\">%s</span></code>@@ @@latex:\\bverb|%s|@@" (org-html-encode-plain-text Modern Documentation across languages) Modern Documentation across languages))

** References :ignoreheading:ignore:
bibliographystyle:unsrt
#+LATEX_HEADER: \addbibresource{./refs.bib}

** LaTeX Options :ignoreheading:ignore:
# Setup for PDF generation via LaTeX export.
#+LATEX_CLASS_OPTIONS: [a4paper]
#+LATEX_HEADER: \usepackage[backend=biber,style=alphabetic]{biblatex}
#+LATEX_HEADER: \newenvironment{notes}{\par\footnotesize}{\par}
#+LATEX_HEADER: \newenvironment{NOTES}{\par\footnotesize}{\par}
#+LATEX_HEADER: \newenvironment{leftcol}{\begin{minipage}{.49\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{rightcol}{\begin{minipage}{.49\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{leftcol30}{\begin{minipage}{.29\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{leftcol40}{\begin{minipage}{.39\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{leftcol60}{\begin{minipage}{.59\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{leftcol70}{\begin{minipage}{.69\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{rightcol30}{\begin{minipage}{.29\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{rightcol40}{\begin{minipage}{.39\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{rightcol60}{\begin{minipage}{.59\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \newenvironment{rightcol70}{\begin{minipage}{.69\textwidth}}{\end{minipage}}
#+LATEX_HEADER: \usepackage{newunicodechar}
#+LATEX_HEADER: \newunicodechar{≈}{$\approx$}
#+LATEX_HEADER: \newunicodechar{⋮}{\vdots}
#+LATEX_HEADER: \newunicodechar{ }{~}
#+LATEX_HEADER: \usepackage{xcolor}
#+LATEX_HEADER: \definecolor{darkred}{rgb}{0.3, 0.0, 0.0}
#+LATEX_HEADER: \definecolor{darkgreen}{rgb}{0.0, 0.3, 0.1}
#+LATEX_HEADER: \definecolor{darkblue}{rgb}{0.0, 0.1, 0.3}
#+LATEX_HEADER: \definecolor{darkorange}{rgb}{1.0, 0.55, 0.0}
#+LATEX_HEADER: \definecolor{sienna}{rgb}{0.53, 0.18, 0.09}
#+LATEX_HEADER: \hypersetup{colorlinks,linkcolor=darkblue,citecolor=darkblue,urlcolor=darkgreen}
#+LATEX_HEADER: \usepackage{newverbs}
#+LATEX_HEADER: \newverbcommand{\rverb}{\color{darkred}}{}
#+LATEX_HEADER: \newverbcommand{\gverb}{\color{darkgreen}}{}
#+LATEX_HEADER: \newverbcommand{\bverb}{\color{darkblue}}{}

* Start Here :ignoreheading:ignore:
* Brief Introduction
** Hello!
- Find me here: https://rgoswami.me
- Who?
  + *Rohit Goswami* MInstP
    - Doctoral Researcher, University of Iceland, Faculty of Physical Sciences
#+begin_leftcol
[[file:logos/physUoI.png]]
#+ATTR_HTML: :width 50% :height 50%
file:logos/rannisLogo.png
#+ATTR_HTML: :width 40% :height 40%
[[file:logos/ccLogo.png]]
#+end_leftcol
#+begin_rightcol
#+ATTR_HTML: :width 40% :height 40%
file:logos/EPH_logo.jpg
#+ATTR_HTML: :width 50% :height 40%
[[file:logos/quansightlabs.jpeg]]
#+end_rightcol
** Logistics
#+ATTR_REVEAL: :frag appear
- All contents are [[https://github.com/HaoZeke/haozeke.github.io][hosted on GitHub]]
  + Slides are in ~presentations/lesHouches21~
#+ATTR_REVEAL: :frag appear
- Questions are welcome *anytime*
* Programming Languages
** Motivation
#+begin_quote
“If a program or package (the words are used interchangeably) is to *have a long life* and to be of *wide application* in its field, it is essential for it to be *easily moved* from one machine to another.

It used to be common to dismiss such movement with the statement, *‘There is no such thing as a machine-independent program.’*

Nonetheless, a great many packages *do now move* from one machine to another”cite:lyonUsingAnsFortran1980
#+end_quote

--> Through the magic of *automated coding* and *standards*
** Language Standards
#+begin_quote
“The standard is the contract between the compiler writer and the application developer.”cite:clermanModernFortranStyle2012
#+end_quote

#+BEGIN_SRC ditaa :file images/hello-program.png :cmdline -r -s 2.5 :cache yes
+------+     +----------+  assembly   +-----------+
| Code | --> | Compiler | ----------> | Assembler | ---+
+------+     +----------+             +-----------+    |
  relocatable machine code                             |
+----------------------------<-------------------------+
|
|
|     +--------+  executable  +--------+     +--------+
+---> | Linker | -----------> | Loader | --> | Memory |
      +--------+              +--------+     +--------+
#+END_SRC

#+RESULTS[f1fc83b64fe81184a3a817828e6dd0aec3714f25]:
[[file:images/hello-program.png]]

#+ATTR_REVEAL: :frag appear
- Sadly interpreters are not really Code -> Memory
#+ATTR_REVEAL: :frag appear
  + Python itself is an interpreter which is commonly implemented in C
** Changing Standards
#+begin_leftcol
#+begin_src fortran
character(10) BLAH*8
character*8 :: BLAH_ONE(10)
character(8) :: BLAH_ONE(10)
#+end_src

#+begin_src python
#!/usr/bin/env python
print("Hello World")
print "Hello World"
#+end_src

#+end_leftcol
#+begin_rightcol

#+DOWNLOADED: screenshot @ 2021-09-08 23:12:16
[[file:images/Why_Care_About_New_Standards/2021-09-08_23-12-16_screenshot.png]]

#+end_rightcol
** F77 ∉ F90 always
#+ATTR_HTML: :width 70% :height 70%
[[file:images/Why_Care_About_New_Standards/2021-09-08_23-14-26_screenshot.png]]

#+ATTR_HTML: :width 70% :height 70%
[[file:images/Why_Care_About_New_Standards/2021-09-08_23-14-38_screenshot.png]]
* LFortran
** Introduction
#+DOWNLOADED: screenshot @ 2021-09-09 00:50:56
[[file:images/Introduction/2021-09-09_00-50-56_screenshot.png]]

| *Language* | *Files* | *Lines* |  *Code* | *Comments* | *Blanks* |
|------------+---------+---------+---------+------------+----------|
| C          |       3 |    1023 |     694 |        191 |      138 |
| C Header   |      57 |   14237 |   11416 |       1041 |     1780 |
| CMake      |      11 |     430 |     361 |         16 |       53 |
| C++        |      54 |   30745 |   26911 |       1560 |     2274 |
| C++ Header |       1 |    8938 |    8297 |        348 |      293 |
| FORTRAN    |      20 |    1738 |    1344 |        174 |      220 |
| Python     |       2 |     224 |     191 |          4 |       29 |
|------------+---------+---------+---------+------------+----------|
| *Total*    |   *148* | *57335* | *49214* |     *3334* |   *4787* |
** Structure

#+BEGIN_SRC ditaa :file images/hello-lfortran.png :cmdline -r -s 3.5 :cache yes
+------+     +-----------+     +----------------+
| Code | --> | Abstract  | --> | (ASR) Abstract | ---+
|      |     | Syntax    |     |       Semantic |    |
|      |     | Tree (AST)|     | Representation |    |
+------+     +-----------+     +----------------+    |
                                                     |
          +--------+                                 |
+---------| Passes |--------------<------------------+
|         +--------+
|
|                        +--------+
|                    +-->| Python |
|                    |   +--------+
|                    |
|     +----------+   |   +------+
+---> | Backends | --+-->| LLVM |
      +----------+   |   +------+
                     |
                     |   +-----+
                     +-->| C++ |
                         +-----+
#+END_SRC

#+RESULTS[e593bcddd9ca0862ed60f7f70716ce54612ef366]:
[[file:images/hello-lfortran.png]]

** Features
- Runtime Libraries :: Pure Fortran | Impure
- ASR :: Guarantees compilation --> Wrappers
- Parser :: Currently almost all of F2018; including F77
- LLVM :: Canonical backend, includes compile time evaluated expressions
- Jupyter :: Native execution as a kernel

* Practical Matters
** Numerical Methods 101
$$Ax=b \\
x=A^{-1}b
$$
- Numerical stability issues
- Floating Point Numbers IEEE 754 cite:goldbergWhatEveryComputer1991
- Convergence can be tied to machine epsilon....
  + Or a *magic number* $(1e-5,1e-16)$
  + Or *Chemical/Spectroscopic* accuracy
#+begin_src fortran :exports both
program main
 print*, tiny(0.d0)
end program
#+end_src

#+RESULTS:
: 2.2250738585072014e-308

** Yawn
:PROPERTIES:
:reveal_background: #99e6ff
:END:
#+begin_quote
“I don't care because *I use libraries.* ”
#+end_quote

#+begin_quote
“I don't care because *I write my own algorithms*.”
#+end_quote
** Implementing Sine
#+DOWNLOADED: screenshot @ 2021-09-09 11:10:27
#+ATTR_HTML: :width 80% :height 40%
[[file:images/Implementing_Sine/2021-09-09_11-10-27_screenshot.png]]

#+begin_src fortran
real(dp) function dsin(x) result(r)
real(dp), parameter :: pi = 3.1415926535897932384626433832795_dp
real(dp), intent(in) :: x ! Assume folded to [-2𝜋,2𝜋]
real(dp) :: y, xnew, twoPi, invTwoPi
if (abs(x) < pi/2) then
    r = kernel_dsin(x)
else ! fold to pi/2 from https://realtimecollisiondetection.net/blog/?p=9
    y = modulo(xnew, 2*pi)
    y = min(y, pi - y)
    y = max(y, -pi - y)
    y = min(y, pi - y)
    r = kernel_dsin(y)
end if
end function
#+end_src
*** Folding I
- Symmetric about $𝜋/2$ --> $x-𝜋/2$
[[file:images/Implementing_Sine/2021-09-09_12-43-34_screenshot.png]]
- $x=-abs(x)$
#+DOWNLOADED: screenshot @ 2021-09-09 12:44:54
[[file:images/Implementing_Sine/2021-09-09_12-44-54_screenshot.png]]
*** Folding II
- $x = -abs(x – 𝜋/2) + 𝜋/2$ -> $x=min(x,𝜋-x)$

#+DOWNLOADED: screenshot @ 2021-09-09 12:46:39
[[file:images/Implementing_Sine/2021-09-09_12-46-39_screenshot.png]]
*** Folding III
- Repeat rightward to get $x=max(x,-𝜋-x)$
#+DOWNLOADED: screenshot @ 2021-09-09 12:47:42
[[file:images/Implementing_Sine/2021-09-09_12-47-42_screenshot.png]]
- Complete with $x=min(x,𝜋-x)$

#+DOWNLOADED: screenshot @ 2021-09-09 12:48:04
[[file:images/Implementing_Sine/2021-09-09_12-48-04_screenshot.png]]

** Kernel Sine

#+begin_leftcol
#+DOWNLOADED: screenshot @ 2021-09-09 11:22:47
#+ATTR_HTML: :width 50% :height 50%
[[file:images/Kernel_Sine/2021-09-09_11-22-47_screenshot.png]]
cite:ChevillardJoldesLauter2010

#+begin_src bash
nix-shell -p sollya rlwrap
rlwrap -A sollya
prec=120;
f=sin(x);
d=[-pi/2;pi/2];
# Use min/max poly
p=remez(f,16,d,
        default,1e-16,1e-30);
p; # Returns coefficients
# Zero out even terms
#+end_src
#+end_leftcol

#+begin_rightcol
#+begin_src fortran
! Accurate on [-pi/2,pi/2] to about 1e-16
elemental real(dp) function kernel_dsin2(x) result(res)
real(dp), intent(in) :: x
real(dp), parameter :: S1 = 0.9999999999999990771_dp
real(dp), parameter :: S2 = -0.16666666666664811048_dp
real(dp), parameter :: S3 = 8.333333333226519387e-3_dp
real(dp), parameter :: S4 = -1.9841269813888534497e-4_dp
real(dp), parameter :: S5 = 2.7557315514280769795e-6_dp
real(dp), parameter :: S6 = -2.5051823583393710429e-8_dp
real(dp), parameter :: S7 = 1.6046585911173017112e-10_dp
real(dp), parameter :: S8 = -7.3572396558796051923e-13_dp
real(dp) :: z
z = x*x
res = x * (S1+z*(S2+z*(S3+z*(S4+z*(S5+z*
      (S6+z*(S7+z*S8)))))))
end function
#+end_src
#+end_rightcol

** Auxiliary Functions
#+begin_src fortran
elemental real(dp) function dmodulo(x, y) result(r)
real(dp), intent(in) :: x, y
r = x-floor(x/y)*y
end function

elemental integer function dfloor(x) result(r)
real(dp), intent(in) :: x
if (x >= 0) then
    r = x
else
    r = x-1
end if
end function

elemental real(dp) function dabs(x) result(r)
real(dp), intent(in) :: x
if (x >= 0) then
    r = x
else
    r = -x
end if
end function
#+end_src
** Accuracy
With an evenly spaced grid of ~0.01~:
#+ATTR_REVEAL: :frag appear
 - $1E-16$ over kernel range $-\pi/2, \pi/2$
#+ATTR_REVEAL: :frag appear
 - $1E-16$ over $[-20,20]$
#+ATTR_REVEAL: :frag appear
 - $1E-12$ from $1E5$
#+ATTR_REVEAL: :frag appear
 - $1E-7$ from $1E10$
*** Post Mortem
- The problem turned out to be ~modulo~
  + IEEE defines a remainder for trignometric functions ~ieee754_rem_pio2~
#+begin_quote
Do not *naively assume* "handcrafted" algorithms are IEEE 754 accurate
#+end_quote

* Fortran, C, Python
- F2003 :: Introduced the ~ISO_C_BINDING~
- Described in great detail on [[https://www.fortran90.org/src/best-practices.html#python-interface][fortran90.org]]:
#+begin_src ditaa :file images/hello-stdfcpy.png :cmdline -r -s 1.5 :cache yes
+--------------+ iso_c_binding   +------------+
| Fortran Code | --------------> | Call in C  |
+--------------+ compiler type   +------------+
                  checking              |
                                        v
              +--------+               +--------+
              | Python |               | Cython |
              | Code   |<--------------| cffi   |
              +--------+               +--------+
#+end_src

#+RESULTS[c649e6871e7d2b61cff7d210af3db78f85b0fcc5]:
[[file:images/hello-stdfcpy.png]]

* F2PY
** History
- Developed by Pearu Peterson cite:petersonF2PYToolConnecting2009
  + July 9, 1999 :: ~f2py.py~ --> Fortran to Python Interface Generator (FPIG)
  + January 22, 2000 :: ~f2py2e~ --> Fortran to Python Interface Generator, 2nd edition.
  + July 19, 2007 :: ~numpy.f2py~ --> f2py2e moved to NumPy project. This is current stable code of f2py.
- Used extensively for F77
  + [[https://numpy.org/][NumPy]] cite:waltNumPyArrayStructure2011, [[https://scipy.org/][SciPy]] cite:virtanenSciPyFundamentalAlgorithms2020
  + [[https://msspec.cnrs.fr/][MsSpec]] cite:sebilleauMsSpec1MultipleScattering2011 :)
** Design
#+BEGIN_SRC ditaa :file images/hello-f2py.png :cmdline -r -s 2.5 :cache yes
+------+     +--------------+  uses C syntax in pyf
| Code | --> | crackfortran | ---------->----------+
+------+     +--------------+                      |
    match rules, generate wrappers, build library  |
+----------------------------<---------------------+
|     +---------+ callbacks +--------+
|     | CPython | <---------| Python |
+---> | Library | --------->|  Code  |
      +---------+           +--------+
#+END_SRC

#+RESULTS[7f80fadd5cfd09443054d3693a2d688d9a0b639d]:
[[file:images/hello-f2py.png]]

- A *best effort* wrapper
  + Specifications via ~.pyf~ or inline comments
  + *Not* a compiler
    - Can rewrite code :)
** Roadmap
- Moves about as fast as spectroscopy codes :)
  + Also picking up speed in 2021
- Implementing newer standards (90, 95, 2003, 2008, 2018, 2020Y)
  + Automating guarantees
- Documentation
** Relevance
:PROPERTIES:
:reveal_background: #99e6ff
:END:
#+begin_quote
Writing *efficient* wrappers without being a language lawyer
#+end_quote

* Bonus: Reading Code
** Reading Code I
#+begin_leftcol
#+ATTR_REVEAL: :frag appear
#+begin_src asm
main:
push    rbp
mov     rbp, rsp
mov     DWORD PTR [rbp-4], 3
mov     eax, 0
pop     rbp
ret
__static_initialization_
    and_destruction_0(int, int):
push    rbp
mov     rbp, rsp
sub     rsp, 16
mov     DWORD PTR [rbp-4], edi
mov     DWORD PTR [rbp-8], esi
cmp     DWORD PTR [rbp-4], 1
jne     .L5
cmp     DWORD PTR [rbp-8], 65535
jne     .L5
mov     edi, OFFSET FLAT:_ZStL8
    __ioinit
#+end_src
#+end_leftcol

#+begin_rightcol
#+ATTR_REVEAL: :frag appear
#+begin_src asm
call    std::ios_base::Init::Init()
    [complete object constructor]
mov     edx, OFFSET FLAT:__dso_handle
mov     esi, OFFSET FLAT:_ZStL8__ioinit
mov     edi, OFFSET FLAT:_ZNSt8ios_base4InitD1Ev
call    __cxa_atexit
.L5:
nop
leave
ret
_GLOBAL__sub_I_main:
push    rbp
mov     rbp, rsp
mov     esi, 65535
mov     edi, 1
call    __static_initialization_
    and_destruction_0(int, int)
pop     rbp
ret
#+end_src
#+end_rightcol
#+ATTR_REVEAL: :frag appear
- But who *writes _assembly_* anyway?
** Reading Code II
#+begin_leftcol
#+ATTR_REVEAL: :frag appear
#+begin_src cpp
int main ()
{
  int D.48918;
  {
    int a;
    a = 3;
    D.48918 = 0;
    return D.48918;
  }
  D.48918 = 0;
  return D.48918;
}

void _GLOBAL__sub_I_main.cpp ()
{
  __static_initialization_
      and_destruction_0 (1, 65535);
}
#+end_src
#+end_leftcol

#+begin_rightcol
#+ATTR_REVEAL: :frag appear
#+begin_src cpp
void __static_initialization_
and_destruction_0 (int __initialize_p,
    int __priority)
{
  if (__initialize_p == 1) goto <D.48920>;
  else goto <D.48921>;
  <D.48920>:
  if (__priority == 65535) goto <D.48922>;
  else goto <D.48923>;
  <D.48922>:
  std::ios_base::Init::Init (&__ioinit);
  __cxxabiv1::__cxa_atexit (__dt_comp ,
                 &__ioinit, &__dso_handle);
  goto <D.48924>;
  <D.48923>:
  <D.48924>:
  goto <D.48925>;
  <D.48921>:
  <D.48925>:
}
#+end_src
#+end_rightcol
#+ATTR_REVEAL: :frag appear
- GIMPLE is an *internal* ~gcc~ representation...

** Reading Code III
#+begin_leftcol
#+ATTR_REVEAL: :frag appear
#+begin_src cpp
#include<iostream>

int main() {
    int a=3;
    return 0;
}
#+end_src
#+ATTR_REVEAL: :frag appear
- Better for most people, still a bit lacking for novices
#+end_leftcol

#+ATTR_REVEAL: :frag appear
#+begin_rightcol
- *Assigning an integer*
#+begin_src bash
g++ main.cpp -o file
#+end_src
- Produces a ~file~ binary which can be run as:
#+begin_src bash
./file
#+end_src
- Output :: There is *no* output, but an assignment of an integer with value 3 takes place
#+end_rightcol

#+ATTR_REVEAL: :frag appear
- What about _different languages_?

** Reading Code IV
#+begin_leftcol
#+ATTR_REVEAL: :frag appear
- Maybe ~gcc~ is just an ugly compiler...
#+ATTR_REVEAL: :frag appear
#+begin_src fortran
program main
  integer :: x = 3 + 6
  print *, x
end program
#+end_src
#+ATTR_REVEAL: :frag appear
- ~lfortran~ has a nicer intermediate structure
#+ATTR_REVEAL: :frag appear
#+begin_src bash
conda create -n lf
conda activate lf
conda install lfortran \
    -c conda-forge
lfortran --show-asr consint.f90
#+end_src
#+end_leftcol

#+begin_rightcol

#+DOWNLOADED: screenshot @ 2021-07-16 16:18:43
#+ATTR_REVEAL: :frag appear
[[file:images/Reading_Code_IV/2021-07-16_16-18-43_screenshot.png]]

#+end_rightcol

* Conclusions
** Omitted Topics
#+ATTR_REVEAL: :frag appear
- Web development and design :: Including frameworks and UX
#+ATTR_REVEAL: :frag appear
- Continuous integration :: How to ensure documentation is coupled to working code
#+ATTR_REVEAL: :frag appear
- Benchmarking :: Demonstrating code superiority
#+ATTR_REVEAL: :frag appear
- Code Review Practices :: Scrum and teamwork
#+ATTR_REVEAL: :frag appear
- HPC and Parallelism :: Efficient data usage and algorithms
#+ATTR_REVEAL: :frag appear
- Build systems :: Portability
#+ATTR_REVEAL: :frag appear
- Science :: Also algorithms
- Usage examples :: For ~f2py~ and ~lfortran~
** Key Takeaways
#+begin_leftcol
#+ATTR_REVEAL: :frag appear
- Document at every level
#+ATTR_REVEAL: :frag appear
- Write modern Fortran
  + Use ~ISO_C_BINDINGS~
  + Use ~IEEE~ standards
#+ATTR_REVEAL: :frag appear
- When using F77
  + Use ~f2py~
- Don't be too clever
  + Don't be too accurate
#+end_leftcol

#+begin_rightcol
#+ATTR_REVEAL: :frag appear
- Ensure style guides exist
#+ATTR_REVEAL: :frag appear
- Benchmark
#+ATTR_REVEAL: :frag appear
- Lint automatically
#+ATTR_REVEAL: :frag appear
- Use modern tools
  + [[https://github.com/fortran-lang/fpm][fpm]], [[https://stdlib.fortran-lang.org/][stdlib]]
  + [[https://lfortran.org/][LFortran]]
#+ATTR_REVEAL: :frag appear
- Ask for help -> [[https://fortran-lang.discourse.group/][Fortran Lang]]
#+end_rightcol
* The End
** Acknowledgements
#+DOWNLOADED: screenshot @ 2021-09-09 00:22:06
[[file:images/Acknowledgements/2021-09-09_00-22-06_screenshot.png]]
- [[https://notendur.hi.is//~hj/indexE.html][Prof. Hannes Jónsson]] as my supervisor, [[https://english.hi.is/staff/birgirhr][Prof. Birgir Hrafnkelsson]] as my co-supervisor, and my committee member [[https://english.hi.is/staff/elvarorn][Dr. Elvar Jonsson]]
- [[https://ondrejcertik.com/][Dr. Ondřej Čertík]] at Los Alamos National Laboratory
- [[https://quansight.com/labs][Quansight Labs]] ([[https://rgommers.github.io/][Dr. Ralf Gommers]], [[https://melissawm.github.io/about-me/][Dr. Melissa Weber Mendonça]] and [[https://github.com/pearu][Dr. Pearu Peterson]])
- Family, pets, Groupmembers, *audience*
** Bibliography
:PROPERTIES:
:CUSTOM_ID: bibliography
:END:

printbibliography:refs.bib

** Thanks!
:PROPERTIES:
:reveal_background: #6f4caa
:END:
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# indent-tabs-mode: nil
# org-src-preserve-indentation: t
# End: