Add WIP blog post on time_t
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title: The Year 2038 problem
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date: 2023-03-09
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published: false
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---
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In the year 2038,
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old Unix code is going to run out of bits to store time.
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This is going to be a really big problem,
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and I'm hoping I can surf it into retirement.
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The Y2K Bug
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===========
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Back in the 1990s there was this increasing panic about the
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"Y2K problem".
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These days it seems to be remembered as sort of a joke,
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like "ha ha remember how freaked out they tried to make us?
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And it wound up being a whole lot of nothing."
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A bunch of people,
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including me,
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worked their assses off to make sure nothing bad happened.
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The problem was that a lot of systems written in the 1960s to the 1980s
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stored the year as a 2-digit number.
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You got the full year by adding 1900 to that stored number.
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This made total sense,
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because most people were used to writing the year as,
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like, "63" or "89".
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I was taught in school to use "mm/dd/yy" format on anything needing a date.
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So when it became increasingly clear that "add 1900" wasn't going to work
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when the year became "00",
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a whole lot of people had to go dig through a whole lot of old programs,
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and patch them in various ways to deal with 2000 and beyond.
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Here are a few of the main techniques I saw,
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in order from "patching it up with chewing gum" to
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"fix that will work forever":
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* If the number is 60-99, add 1900. Otherwise add 2000.
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This works only if you're storing dates after 1960,
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and is going to stop working in 2060.
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I guess at this point everyone involved in the 1999 fix
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will probably be dead, so it'll be someone else's problem.
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* Alter things to store years with more than two numbers.
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So the year 2000 is stored as 100 (1900 + 100 = 2000).
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It's weird when you look at the raw data,
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but it might mean you can keep using the rest of the program,
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which means you're able to get the fix in quickly.
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* Store time as a `time_t`, which counts the number of seconds
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since January 1, 1970 in Coordinated Universal Time (UTC).
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I'll talk about the problem with this below.
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* Store the year as a 4-digit number,
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which will keep working for another 8000 years,
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and also allows you to store dates going back to the beginning
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of most governments on Earth.
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When January 1, 2000 rolled around,
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there were still a couple of problems.
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I remember one payroll company was dating checks wrong,
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I think an insurance company had some sort of issue they patched pretty quickly,
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but for the most part,
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everything kept running along smoothly,
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and all the people like me who had stayed up all night in the data center
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waiting for some big emergency
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breathed a big sigh of relief and went to bed.
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The Year 2038 Problem
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=====================
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That third example of a fix uses the Unix `time_t`,
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which is a 32-bit signed integer.
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Bits?
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-----
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Bits are talked about a lot with computers,
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but hardly ever explained.
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Here's a really brief introduction
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based on my years of experience teaching binary to high school students.
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Let's start by talking about decimal, though.
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| # of digits | how many muffins you can count | number of different values |
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| ---- | ---- | ---- |
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| 1 | 0 - 9 | 10 |
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| 2 | 0 - 99 | 100 |
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| 3 | 0 - 999 | 1000 |
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| 4 | 0 - 9999 | 10000 |
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Get it?
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Now let's talk about binary:
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| # of bits | how many muffins you can count | number of different values |
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| ---- | ---- |
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| 1 | 0 - 1 | 2 |
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| 2 | 0 - 3 | 4 |
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| 3 | 0 - 7 | 8 |
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| 4 | 0 - 15 | 16 |
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| 5 | 0 - 31 | 32 |
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| 6 | 0 - 63 | 64 |
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| 7 | 0 - 127 | 128 |
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| 8 | 0 - 255 | 256 |
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See the pattern?
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Every time you add a bit,
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you get twice as many values.
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Let's extend that table:
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| # of bits | how many muffins you can count | number of different values |
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| ---- | ---- |
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| 1 | 0 - 1 | 2 |
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| 2 | 0 - 3 | 4 |
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| 3 | 0 - 7 | 8 |
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| 4 | 0 - 15 | 16 |
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| 5 | 0 - 31 | 32 |
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| 6 | 0 - 63 | 64 |
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| 7 | 0 - 127 | 128 |
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| 8 | 0 - 255 | 256 |
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| ⋮ | ⋮ | ⋮ | ⋮ |
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| 30 | 0 - 1073741823 | 1073741824 |
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| 31 | 0 - 2147483647 | 2147483648 |
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| 32 | 0 - 4294967297 | 4294967296 |
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