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Silveira Neto Posts

On children – Khalil Gibran

Published by Silveira on 2025-10-02

Your children are not your children.
They are the sons and daughters of Life’s longing for itself.
They come through you but not from you,
And though they are with you yet they belong not to you.

You may give them your love but not your thoughts,
For they have their own thoughts.
You may house their bodies but not their souls,
For their souls dwell in the house of tomorrow, which you cannot visit, not even in your dreams.

You may strive to be like them, but seek not to make them like you.
For life goes not backward nor tarries with yesterday.
You are the bows from which your children as living arrows are sent forth.
he archer sees the mark upon the path of the infinite, and He bends you with His might that His arrows may go swift and far.
Let your bending in the archer’s hand be for gladness;
For even as He loves the arrow that flies, so He loves also the bow that is stable.

Those panels in Persepolis

Published by Silveira on 2025-09-24

Persepolis is an autobiographical graphic novel series by Marjane Satrapi, chronicling her childhood and adolescence in Iran and Austria during and after the Islamic Revolution. You can usually find it between the top 10 best comic books of all times, in any good list.

There is a particular small sequence of panels that’s not particularly important to the plot but really stuck with me. Itt comes back to my mind once in a while.

Simple japanese lantern in OpenSCAD

Published by Silveira on 2025-09-19

Blender rendering:

Blender rendering of a simple japanese lantern in OpenSCAD

OpenSCAD definitions:

alpha=1;

module chamber() {
    translate([0,0,2])
    scale(v=0.8)
        difference() {
            cube([3,3,3]);

            translate([0,1,1])
                cube([3,1,1]);

            translate([1,0,1])
                cube([1,3,1]);
        }
}

module pedestal() {
    cube([1,1,1]);
    translate([0,2,0])
        cube();
    translate([2,0,0])
        cube();
    translate([2,2,0])
        cube();
    translate([0,0,1])
        cube([3,3,1]);
}

module hat() {
    translate([1.25,1.25,4.25])
        rotate(45)
            cylinder(1,3,1,$fn=4);
}

color("lightblue", alpha)
    translate([-0.25,-0.25,0])
        pedestal();

color("lightgreen", alpha)
    chamber();

color("lightcoral", alpha)
    hat();

Live demo

commuting calculations

Published by Silveira on 2025-09-11

How much does it cost me per day and per month to drive to work.

home_to_work = 5.4 miles (~8.7 km)
work_to_home = 5.8 miles (~9.3 km)
round_trip = home_to_work + work_to_home = 11.2 miles (18 km)
car_mpg = 14 mpg 

gallons_per_trip = round_trip / car_mpg = 0.8 gallons
gallons_price = $3
gas_cost_per_trip = gallons_per_trip * gallons_price = $2.4

parking = $10.50 (after subsidies)

commute_per_day_by_car_cost = parking + gas_cost_per_trip = $12.9
commute_per_month_by_car_cost = commute_per_day_by_car_cost * 20 = $258

Parking is the dominant cost. My car mpg is terrible, however that barely makes a dent on the costs.

Published by Silveira on 2025-07-09

“Quem passou pela vida em branca nuvem
E em plácido repouso adormeceu,
Quem não sentiu o frio da desgraça,
Quem passou pela vida e não sofreu,
Foi espectro de homem, e não homem,
Só passou pela vida, não viveu.”

Francisco Otaviano

Com Puta Ação

Published by Silveira on 2025-04-30

No Ensino Médio, nos íamos ao laboratório de informática estudar programação. A rotina era sempre a mesma: ir no site da Olimpíada Brasileira de Programação, baixar uns problemas (problemas estilo LeetCode), e passar horas programando em Pascal ou C.

Eis que um dia o site não abria mais. Outros sites abriam mas o site da Sociedade Brasileira de Computação não abria. Até que encontramos o culpado: haviam instalado um firewall no laboratório. O algoritmo do firewall era tão pudico quanto ingênuo. Ele bloqueava URLs que continham alguma palavra de uma lista de palavras bloqueadas. A URL continha a palavra computação. Embora computação por si só não seja digno de censura, o algoritmo ficou escandalizado com a “puta” de “computação”.

Esses dias descobri que existe um nome pra isso, Problema Scunthorpe:

O problema de Scunthorpe é o bloqueio não intencional de conteúdo online por um filtro de spam ou mecanismo de busca porque seu texto contém uma sequência (ou subsequência) de letras que parecem ter um significado obsceno ou inaceitável.

O nome vem da cidade de Scunthorpe da Inglaterra que já teve vários problemas online devido ao “cunt” de “Scunthorpe”.

bash and wget to download a lot of files

Published by Silveira on 2025-04-21

Problem:

  • Download 500 large files.
  • Files follow the pattern data_1.zip, data_2.zip, … data_500.zip.
  • All the files are in “https://examples.com/downloads”.
  • Files have from kilobytes to gigabytes in size.

Solution:

  • A naive Bash script to download the files using wget.
  • It is set to use wget with -c (continue). This will skip files already downloaded and continue files that have been interrupted. This only works with FTP/HTTP servers that support the “Range” header.
#!/bin/bash
set -euxo pipefail

PREFIX="https://examples.com/downloads/data_"

for i in $(seq 1 500); do
  wget -c "$PREFIX"_"$i".zip
done