Notes on CAS and git.

notes/.obsidian/plugins/obsidian-to-anki-plugin/data.json

@@ -89,7 +89,7 @@
     "algorithms/index.md": "cd7c7ba91fb2f961c9f2437777e8e2ac",
     "algorithms/sorting/index.md": "2d5a18a3079d96fa9e3d4289181a8b6c",
     "algorithms/sorting/insertion-sort.md": "00e4edb132d473b0516fde3307ebae30",
-    "bash/index.md": "3dfeb538d781e4645e3aaaf32beb1034",
+    "bash/index.md": "3e4738d8d3531bb7a5afc53a2d73036c",
     "bash/prompts.md": "61cb877e68da040a15b85af76b1f68ba",
     "bash/quoting.md": "b1d8869a91001f8b22f0cdc54d806f61",
     "bash/robustness.md": "7ab094b95ba2bfa885adba8e9efedf68",
@@ -122,7 +122,7 @@
     "_journal/2024-02-02.md": "a3b222daee8a50bce4cbac699efc7180",
     "_journal/2024-02-01.md": "3aa232387d2dc662384976fd116888eb",
     "_journal/2024-01-31.md": "7c7fbfccabc316f9e676826bf8dfe970",
-    "logic/equiv-trans.md": "4a781f0d21ee0942445cd31da3ec396f",
+    "logic/equiv-trans.md": "1f2d5823f128b8fdb526436e83a206ff",
     "_journal/2024-02-07.md": "8d81cd56a3b33883a7706d32e77b5889",
     "algorithms/loop-invariants.md": "cbefc346842c21a6cce5c5edce451eb2",
     "algorithms/loop-invariant.md": "29f9f9090a3109890d333a78acc18b50",
@@ -190,7 +190,7 @@
     "combinatorics/inclusion-exclusion.md": "ca5c967be774ce204f1ca47cc8df14b8",
     "_journal/2024-02-21.md": "b9d944ecebe625da5dd72aeea6a916a2",
     "_journal/2024-02/2024-02-20.md": "af2ef10727726200c4defe2eafc7d841",
-    "algebra/radices.md": "88c6c5657eca99f3d274f0c3fc0e3af0",
+    "algebra/radices.md": "4ffc8525f2b877c0d17e3359870797fe",
     "_journal/2024-02-22.md": "e01f1d4bd2f7ac2a667cdfd500885a2a",
     "_journal/2024-02/2024-02-21.md": "f423137ae550eb958378750d1f5e98c7",
     "_journal/2024-02-23.md": "219ce9ad15a8733edd476c97628b71fd",
@@ -208,8 +208,15 @@
     "_journal/2024-02/2024-02-25.md": "426be827fe8483e4ab432304a2aa6df3",
     "_journal/2024-02-27.md": "851180f1f7c1aaacd4c0b0ec2639bdf2",
     "_journal/2024-02/2024-02-26.md": "417b84be5d96f9d8adcdedca3b68b141",
-    "_journal/2024-02-28.md": "3d69115853814aaff435b3a4c05f97b7",
+    "_journal/2024-02-28.md": "7489377c014a2ff3c535d581961b5b82",
-    "_journal/2024-02/2024-02-27.md": "f75a0d04a875aeee932343dae0c78768"
+    "_journal/2024-02/2024-02-27.md": "f75a0d04a875aeee932343dae0c78768",
+    "filesystems/index.md": "cbd2b0290a3ba3b32abec4bd8bfefad5",
+    "filesystems/cas.md": "34906013a2a60fe5ee0e31809b4838aa",
+    "git/objects.md": "b49015b8ebffc2c976d97b2484c74448",
+    "git/index.md": "83d2d95fc549d9e8436946c7bd058d15",
+    "encoding/integer.md": "5dd3a961bf259e53da207209051b8335",
+    "_journal/2024-02-29.md": "f610f3caed659c1de3eed5f226cab508",
+    "_journal/2024-02/2024-02-28.md": "7489377c014a2ff3c535d581961b5b82"
   },
   "fields_dict": {
     "Basic": [

notes/_journal/2024-02-29.md

@@ -0,0 +1,21 @@
+---
+title: "2024-02-29"
+---
+
+- [x] Anki Flashcards
+- [x] KoL
+- [ ] Sheet Music (10 min.)
+- [x] Go (1 Life & Death Problem)
+- [ ] Korean (Read 1 Story)
+- [ ] Interview Prep (1 Practice Problem)
+- [ ] Log Work Hours (Max 3 hours)
+
+* 101weiqi (serial numbers)
+	* Q-349924
+	* Q-99982
+	* Q-285489
+	* Q-85874
+	* Q-265576
+	* Q-11420
+* TODO
+	* Watch database courses and read

notes/_journal/2024-02/2024-02-28.md

@@ -5,10 +5,10 @@ title: "2024-02-28"
 - [x] Anki Flashcards
 - [x] KoL
 - [ ] Sheet Music (10 min.)
-- [ ] Go (1 Life & Death Problem)
+- [x] Go (1 Life & Death Problem)
 - [ ] Korean (Read 1 Story)
 - [ ] Interview Prep (1 Practice Problem)
-- [ ] Log Work Hours (Max 3 hours)
+- [x] Log Work Hours (Max 3 hours)
 
 * 101weiqi (serial numbers)
 	* Q-314990
@@ -17,3 +17,5 @@ title: "2024-02-28"
 	* Q-51685
 	* Q-11821
 	* Q-5014
+* Add notes on `SIGABRT`.
+* First pass on "Git Internals" in "Pro Git".

notes/algebra/radices.md

@@ -276,7 +276,7 @@ END%%
 
 %%ANKI
 Basic
-Which hexadecimal digits have a leading `1` bit?
+Which hexadecimal digits encode binary with a leading `1` bit?
 Back: `8` through `F`
 Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
 Tags: binary::hex
@@ -285,7 +285,7 @@ END%%
 
 %%ANKI
 Basic
-Which hexadecimal digits have a leading `0` bit?
+Which hexadecimal digits encode binary with a leading `0` bit?
 Back: `0` through `7`
 Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
 Tags: binary::hex

notes/encoding/integer.md

@@ -126,8 +126,8 @@ END%%
 
 %%ANKI
 Basic
-*Why* is it $UMax = 2 \cdot TMax + 1$?
+Provide a combinatorial explanation on why $UMax$ equals $2 \cdot TMax + 1$.
-Back: All bit strings representing negative numbers in two's-complement are positive in unsigned encoding.
+Back: There is one more negative number than positive numbers represented in two's-complement.
 Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
 <!--ID: 1708613447880-->
 END%%

notes/filesystems/cas.md

@@ -0,0 +1,103 @@
+---
+title: Content-Addressable Storage
+TARGET DECK: Obsidian::STEM
+FILE TAGS: fs::cas
+tags:
+  - cas
+  - fs
+---
+
+## Overview
+
+CAS (**c**ontent-**a**ddressed **s**torage) refers to storage that allows retrieval based on content (as opposed to name or location). Usually the contents of a file are passed through a cryptographic hash function to generate a key that can be used for subsequent retrieval.
+
+%%ANKI
+Basic
+What is content-addressed storage?
+Back: A method for storing information such that it can be retrieved based on its content.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255543-->
+END%%
+
+%%ANKI
+Basic
+What is considered the "opposite" of content-addressed storage?
+Back: Location-addressed storage.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255547-->
+END%%
+
+%%ANKI
+Basic
+What is CAS an acronym for?
+Back: **C**ontent-**a**ddressed **s**torage.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255550-->
+END%%
+
+%%ANKI
+Cloze
+{1:Content}-addressed is to {2:URNs} whereas {2:location}-addressed is to {1:URLs}.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255553-->
+END%%
+
+%%ANKI
+Basic
+Interpreted as a key-value store, what is a "key" in a CAS system?
+Back: The digest produced when running content through a cryptographic hash function.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255556-->
+END%%
+
+%%ANKI
+Basic
+Interpreted as a key-value store, what is a "value" in a CAS system?
+Back: The actual content being stored.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255559-->
+END%%
+
+%%ANKI
+Basic
+In the context of CAS, what is a "content address"?
+Back: A digest produced when running content through a cryptographic hash function.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255562-->
+END%%
+
+%%ANKI
+Cloze
+Content addresses are an alternative to {location} addresses found in traditional filesystems.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255565-->
+END%%
+
+%%ANKI
+Basic
+Why are CAS systems sometimes called "fixed content storage"?
+Back: CAS is normally used for files that are not frequently edited.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255567-->
+END%%
+
+%%ANKI
+Basic
+How is it CAS systems ensure file uniqueness?
+Back: An attempt to store an already stored file will generate the same key as before.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255570-->
+END%%
+
+%%ANKI
+Basic
+How is it CAS systems ensure file's remain unchanged?
+Back: A file's key will always be the same provided the content has not changed.
+Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+<!--ID: 1709177255573-->
+END%%
+
+## References
+
+* “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
+* Scott Chacon, _Pro Git_, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).

notes/filesystems/index.md

@@ -0,0 +1,3 @@
+---
+title: Filesystems
+---

notes/git/index.md

@@ -0,0 +1,3 @@
+---
+title: Git
+---

notes/git/objects.md

@@ -0,0 +1,174 @@
+---
+title: Objects
+TARGET DECK: Obsidian::STEM
+FILE TAGS: fs::cas git
+tags:
+  - cas
+  - fs
+  - git
+---
+
+## Overview
+
+%%ANKI
+Basic
+What cryptographic hash function does git use internally?
+Back: SHA-1
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255577-->
+END%%
+
+%%ANKI
+Basic
+How many bytes make up a SHA-1 digest?
+Back: 20
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255580-->
+END%%
+
+%%ANKI
+Basic
+How many hexadecimal digits make up a SHA-1 digest?
+Back: 40
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255584-->
+END%%
+
+%%ANKI
+Basic
+How is a SHA-1 digest typically represented?
+Back: As a string of 40 hexadecimal digits.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255589-->
+END%%
+
+%%ANKI
+Basic
+What is "oid" an acronym for?
+Back: **O**bject **id**.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255594-->
+END%%
+
+%%ANKI
+Basic
+What *is* an object id?
+Back: The digest produced when hashing/storing content.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255599-->
+END%%
+
+%%ANKI
+Basic
+What does it mean for git to be a content-addressed storage system?
+Back: Keys generated from hashing content are used to later retrieve said content.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+Tags: fs::cas
+<!--ID: 1709177255603-->
+END%%
+
+%%ANKI
+Cloze
+Interpreted as a key-value store, {oids} are to keys as {objects} are to values.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+Tags: fs::cas
+<!--ID: 1709177255607-->
+END%%
+
+%%ANKI
+Basic
+Why prefer term "oid" over e.g. "SHA-1 digest" or similar?
+Back: Git is transitioning to the use of other cryptographic hash functions.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255612-->
+END%%
+
+%%ANKI
+Basic
+What is a "porcelain" command?
+Back: A user-friendly command.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255618-->
+END%%
+
+%%ANKI
+Basic
+What is a "plumbing" command?
+Back: A lower-level command.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255622-->
+END%%
+
+%%ANKI
+Cloze
+{Porcelain} commands are more user-friendly than {plumbing} commands.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255627-->
+END%%
+
+%%ANKI
+Basic
+What plumbing subcommand is used to generate an oid?
+Back: `hash-object`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255632-->
+END%%
+
+%%ANKI
+Basic
+The `hash-object` subcommand optionally stores the resulting object in what directory?
+Back: `.git/objects`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255637-->
+END%%
+
+%%ANKI
+Cloze
+The {object database} refers to the {`.git/objects`} directory.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255644-->
+END%%
+
+%%ANKI
+Basic
+What does the `hash-object` subcommand return?
+Back: The computed object id.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255651-->
+END%%
+
+%%ANKI
+Basic
+What optional functionality does the `hash-object` subcommand support?
+Back: It can write an object into the object database.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255659-->
+END%%
+
+%%ANKI
+Basic
+What flag lets the `hash-object` subcommand write to the object database?
+Back: `-w`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255664-->
+END%%
+
+%%ANKI
+Basic
+Where does object e.g. `d670460b4b4aece5915caf5c68d12f560a9fe3e4` live in the object database?
+Back: At `.git/objects/d6/70460b4b4aece5915caf5c68d12f560a9fe3e4`.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255668-->
+END%%
+
+%%ANKI
+Basic
+What regular files exist in the object database after `git init`?
+Back: None.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255672-->
+END%%
+
+## References
+
+* Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).

notes/logic/equiv-trans.md

@@ -863,7 +863,7 @@ END%%
 
 %%ANKI
 Basic
-How do define $s'$ such that $s(E_e^x) = s'(E)$?
+How do you define $s'$ such that $s(E_e^x) = s'(E)$?
 Back: $s' = (s; x{:}s(e))$.
 Reference: Gries, David. *The Science of Programming*. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
 <!--ID: 1707939006292-->