Notes on endianness.

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

@@ -80,7 +80,7 @@
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-    "algorithms/sorting/insertion-sort.md": "e26909d0b4097e8e072d0b19667bf586",
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@@ -88,8 +88,8 @@
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@@ -103,9 +103,9 @@
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     "templates/daily.md": "7866014e730e85683155207a02e367d8",
-    "posix/regexp.md": "e41bf86b770958316df1e20578d6020f",
+    "posix/regexp.md": "43825a1b9ed0dd7eeb1b6fe35c928bfe",
     "journal/2024-02-04.md": "e2b5678fc53d7284b71ed6820c02b954",
-    "gawk/regexp.md": "dbd5f9f85a2658b304a635a47379e871",
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   "fields_dict": {
     "Basic": [

notes/_journal/2024-02-11.md

@@ -1,5 +1,5 @@
 ---
-title: "2024-02-09"
+title: "2024-02-11"
 ---
 
 - [x] Anki Flashcards
@@ -10,5 +10,4 @@ title: "2024-02-09"
 - [ ] Interview Prep (1 Practice Problem)
 - [ ] Log Work Hours (Max 3 hours)
 
-* Logged information about prominent predefined `awk` variables.
-* Created flashcards for C data type declarations.
+* Notes on endianness.

notes/_journal/2024-02/2024-02-09.md

@@ -0,0 +1,16 @@
+---
+title: "2024-02-09"
+---
+
+- [x] Anki Flashcards
+- [x] KoL
+- [x] Sheet Music (10 min.)
+- [ ] OGS (1 Life & Death Problem)
+- [x] Korean (Read 1 Story)
+- [ ] Interview Prep (1 Practice Problem)
+- [x] Log Work Hours (Max 3 hours)
+
+* Logged information about prominent predefined `awk` variables.
+* Created flashcards for C data type declarations.
+* Added notes on bubble sort.
+* Added notes on existential/universal quantification.

notes/_journal/2024-02/2024-02-10.md

@@ -0,0 +1,13 @@
+---
+title: "2024-02-10"
+---
+
+- [x] Anki Flashcards
+- [x] KoL
+- [x] Sheet Music (10 min.)
+- [x] OGS (1 Life & Death Problem)
+- [ ] Korean (Read 1 Story)
+- [ ] Interview Prep (1 Practice Problem)
+- [ ] Log Work Hours (Max 3 hours)
+
+* Some reading around how `awk` handles field separators.

notes/algorithms/sorting/bubble-sort.md

@@ -20,6 +20,14 @@ Adaptive    | Yes
 
 ![[bubble-sort.gif]]
 
+%%ANKI
+Basic
+Describe bubble sort in a single sentence.
+Back: Repeatedly swap the smaller of adjacent records downward.
+Reference: Thomas H. Cormen et al., *Introduction to Algorithms*, 3rd ed (Cambridge, Mass: MIT Press, 2009).
+<!--ID: 1707589393196-->
+END%%
+
 %%ANKI
 Basic
 What is bubble sort's best case runtime?

notes/algorithms/sorting/insertion-sort.md

@@ -20,6 +20,14 @@ Adaptive    | Yes
 
 ![[insertion-sort.gif]]
 
+%%ANKI
+Basic
+Describe insertion sort in a single sentence.
+Back: Repeatedly put the next record into a sorted array from right to left.
+Reference: Thomas H. Cormen et al., *Introduction to Algorithms*, 3rd ed (Cambridge, Mass: MIT Press, 2009).
+<!--ID: 1707589393194-->
+END%%
+
 %%ANKI
 Basic
 What is insertion sort's best case runtime?

notes/algorithms/sorting/selection-sort.md

@@ -20,6 +20,15 @@ Adaptive    | No
 
 ![[selection-sort.gif]]
 
+
+%%ANKI
+Basic
+Describe selection sort in a single sentence.
+Back: Repeatedly put the smallest unsorted record at the end of a sorted array.
+Reference: Thomas H. Cormen et al., *Introduction to Algorithms*, 3rd ed (Cambridge, Mass: MIT Press, 2009).
+<!--ID: 1707589393190-->
+END%%
+
 %%ANKI
 Basic
 What is selection sort's best case runtime?

notes/binary/endianness.md

@@ -0,0 +1,119 @@
+---
+title: Endianness
+TARGET DECK: Obsidian::STEM
+FILE TAGS: binary::endian
+tags:
+  - binary
+  - endian
+---
+
+## Overview
+
+Platforms with multi-byte objects must establish the object's address and byte ordering. Objects are typically addressed by the smallest address of the bytes used. Bytes are ordered either in **big-endian** or **little-endian**. In big-endian, the most significant byte is listed first. In little-endian, the least significant byte is ordered first.
+
+%%ANKI
+Basic
+Platforms with multi-byte objects must establish what two conventions?
+Back: The object's address and byte ordering.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283766-->
+END%%
+
+%%ANKI
+Basic
+How are multi-byte objects typically addressed?
+Back: By the smallest address of the bytes used.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283768-->
+END%%
+
+%%ANKI
+Basic
+How are bytes of multi-byte objects typically ordered?
+Back: As big-endian or little-endian.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283770-->
+END%%
+
+%%ANKI
+Basic
+What is endianness?
+Back: The ordering of bytes of a multibyte object.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283771-->
+END%%
+
+%%ANKI
+Basic
+What does it mean for a byte to be "most significant"?
+Back: It contribute most to the byte's (decimal) value.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283773-->
+END%%
+
+%%ANKI
+Basic
+What does it mean for a byte to be "least significant"?
+Back: It contribute least to the byte's (decimal) value.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283774-->
+END%%
+
+%%ANKI
+Basic
+What does it mean to be big-endian?
+Back: The most significant byte is ordered first.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283776-->
+END%%
+
+%%ANKI
+Basic
+What does it mean to be little-endian?
+Back: The least significant byte is ordered first.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283777-->
+END%%
+
+%%ANKI
+Basic
+How are bytes of `int32_t x = 0x01234567` written in big-endian?
+Back: `0x01 0x23 0x45 0x67`
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+Tags: c
+<!--ID: 1707661283779-->
+END%%
+
+%%ANKI
+Basic
+How are bytes of `int32_t x = 0x01234567` written in little-endian?
+Back: `0x67 0x45 0x23 0x01`
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+Tags: c
+<!--ID: 1707661283780-->
+END%%
+
+%%ANKI
+Cloze
+Many microprocessors chips are {bi-endian} meaning they can be {configured as either big- or little-endian}.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707661283782-->
+END%%
+
+```c
+#include <stdint.h>
+#include <stdio.h>
+
+int main() {
+  int32_t x = 0x01234567;
+  for (int i = 0; i < 4; ++i) {
+    printf("%.2x ", ((unsigned char *)(&x))[i]);
+  }
+}
+```
+
+The above snippet can be used to check endianness on the current machine. If big-endian, the output should be `01 23 45 67`. If little-endian, `67 45 23 01`.
+
+## Reference
+
+* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.

notes/binary/hexadecimal.md

@@ -224,4 +224,4 @@ END%%
 
 ## Reference
 
-* Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.

notes/c/declarations.md

@@ -36,6 +36,22 @@ Back: It can only represent nonnegative values.
 Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
 END%%
 
+%%ANKI
+Basic
+How large is a word?
+Back: This is a machine-dependent value.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707657889227-->
+END%%
+
+%%ANKI
+Basic
+What word sizes are typically nowadays?
+Back: 32- and 64-bit word sizes.
+Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
+<!--ID: 1707657889230-->
+END%%
+
 %%ANKI
 Cloze
 `char` *typically* represents {1} byte(s) on a 64-bit platform.

notes/gawk/index.md

@@ -293,6 +293,36 @@ Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 202
 <!--ID: 1706883732944-->
 END%%
 
+%%ANKI
+Basic
+What is the output of the following?
+```bash
+$ echo ' abc' | awk '{ print }'
+```
+Back: `‏‏‎ ‎abc` (with leading whitespace)
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833559-->
+END%%
+
+%%ANKI
+Basic
+What is the output of the following?
+```bash
+$ echo ' abc' | awk ' { $1 = $1; print }'
+```
+Back: `abc` (without leading whitespace)
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833561-->
+END%%
+
+%%ANKI
+Basic
+How is `$$0` rebuilt after assignment `$1 = $1`?
+Back: By intercalating `OFS` between values of `$1` through `NF`.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833562-->
+END%%
+
 ## Exit Status
 
 On success, `gawk` exits with status code `EXIT_SUCCESS`. On failure, with status code `EXIT_FAILURE`. On fatal error, `gawk` exists with status code `2`. #c

notes/gawk/regexp.md

@@ -72,8 +72,8 @@ END%%
 
 %%ANKI
 Basic
-Why is it recommended to avoid using `^`/`$` in `RS`?
-Back: These anchors match the beginning/end of a string, not of a line.
+Why is it recommended to avoid using `^` and `$$` in `RS`?
+Back: These anchors match the beginning and end of a string, not of a line.
 Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
 <!--ID: 1707310981375-->
 END%%

notes/gawk/variables.md

@@ -118,7 +118,7 @@ END%%
 %%ANKI
 Basic
 What implementation detail inspires avoiding `RS = "\0"`?
-Back: Most `awk` implementations store strings internally as C-style strings?
+Back: Most `awk` implementations store strings internally as C-style strings.
 Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
 <!--ID: 1707310981392-->
 END%%
@@ -133,6 +133,9 @@ END%%
 
 * `NF` (**N**umber of **F**ields)
 	* The 1-indexed number of fields found in the current record.
+* `FS` (**F**ield **S**eparator)
+	* The separator used to distinguish fields from one another.
+	* Defaults to `" "` which is a special character for **runs** of spaces, tabs, and newlines.
 
 %%ANKI
 Basic
@@ -165,6 +168,51 @@ Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 202
 <!--ID: 1707405259930-->
 END%%
 
+%%ANKI
+Cloze
+The {`FS`} variable is used to change the {field separator}.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833549-->
+END%%
+
+%%ANKI
+Cloze
+{`FS`} is to `awk` as {`IFS`} is to Bash.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+/END%%
+
+%%ANKI
+Basic
+What is the default value of `FS`?
+Back: `" "`
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833552-->
+END%%
+
+%%ANKI
+Basic
+What value of `FS` is specially handled?
+Back: `" "`
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833555-->
+END%%
+
+%%ANKI
+Basic
+How is `FS = " "` interpreted?
+Back: As a contiguous sequence of spaces, tabs, and newlines.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833556-->
+END%%
+
+%%ANKI
+Basic
+What distinguishes `FS` value `" "` and `[ \t\n]+`?
+Back: When set to the former, `awk` strips leading and trailing whitespace from each record.
+Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)
+<!--ID: 1707618833558-->
+END%%
+
 ## References
 
 * Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)

notes/logic/equiv-trans.md

@@ -582,7 +582,7 @@ END%%
 %%ANKI
 Basic
 What is a "theorem" in the equivalence-transformation formal system?
-Back: An equality derived from the axioms and inference rules.
+Back: An equivalence derived from the axioms and inference rules.
 Reference: Gries, David. *The Science of Programming*. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
 <!--ID: 1707316178712-->
 END%%
@@ -668,7 +668,7 @@ END%%
 
 %%ANKI
 Basic
-Where are $\land$ and $\lor$ found within a proposition in DNF?
+Where are $\land$ and $\lor$ found within a DNF proposition?
 Back: $\lor$ separates disjuncts containing $\land$.
 Reference: Gries, David. *The Science of Programming*. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
 <!--ID: 1707311868998-->
@@ -692,7 +692,7 @@ END%%
 
 %%ANKI
 Basic
-Where are $\land$ and $\lor$ found within a proposition in CNF?
+Where are $\land$ and $\lor$ found within a CNF proposition?
 Back: $\land$ separates conjuncts containing $\lor$.
 Reference: Gries, David. *The Science of Programming*. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
 <!--ID: 1707311869003-->

notes/posix/regexp.md

@@ -150,6 +150,14 @@ Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [ht
 <!--ID: 1707050923650-->
 END%%
 
+%%ANKI
+Basic
+How is the `*` operator written equivalently as an interval expression?
+Back: `{0,}`
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707654685031-->
+END%%
+
 %%ANKI
 Basic
 What does the `+` operator do?
@@ -158,6 +166,14 @@ Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [ht
 <!--ID: 1707050923656-->
 END%%
 
+%%ANKI
+Basic
+How is the `+` operator written equivalently as an interval expression?
+Back: `{1,}`
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707654685034-->
+END%%
+
 %%ANKI
 Basic
 What does the `?` operator do?
@@ -166,6 +182,14 @@ Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [ht
 <!--ID: 1707050923662-->
 END%%
 
+%%ANKI
+Basic
+How is the `?` operator written equivalently as an interval expression?
+Back: `{0,1}`
+Reference: “POSIX Basic Regular Expressions,” accessed February 4, 2024, [https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions](https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions).
+<!--ID: 1707654685036-->
+END%%
+
 * `{n}`, an **interval expression**, matches the preceding element `n` times.
 	* `{n,}` matches the preceding element at least `n` times.
 	* `{n,m}` matches the preceding element between `n` and `m` times.