content/blog/2023-03-09-time_t/index.md

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

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