added fizzbuzz chapter

.vscode/settings.json

@@ -10,6 +10,8 @@
 		"iostream",
 		"memcpy",
 		"pseudocode",
+		"stringstream",
+		"strncpy",
 		"struct",
 		"structs"
 	],

README.md

@@ -53,6 +53,7 @@ the 64 bit ARM Instruction Set Architecture (ISA).
 | 5 | [Interlude - Load and Store](./section_1/regs/ldr.md) |
 | 6 | [Calling and Returning From Functions](./section_1/funcs/README.md) |
 | 7 | [Passing Parameters To Functions](./section_1/funcs/README2.md) |
+| 8 | [FizzBuzz - a Complete Program](./section_1/fizzbuzz/README.md) |
 
 ## Section 2 - Stuff
 

section_1/fizzbuzz/README.md

@@ -0,0 +1,51 @@
+# Section 1 / Chapter 8 / FizzBuzz
+
+In this chapter we build the classic tech interview question: FizzBuzz.
+
+The idea is simple. Write a program that enumerates the integers from 0 to some stopping value, perhaps 100.
+
+For each integer:
+
+* If it is a multiple of 3, print Fizz
+
+* If it is a multiple of 5, print Buzz
+
+* If it is a multiple of both 3 *and* 5, print FizzBuzz
+
+* Otherwise, if none of the above applies, print the integer.
+
+The interviewer's hope is that you get twisted in knots trying
+to navigate the case where the integer is a multiple of both 3 and
+5. There are many ways to solve this challenge.
+
+One way might be to test for being a multiple of 15 *first* and print
+FizzBuzz if true. Then test against 3 and then against 5.
+
+Another way is to accumulate the correct out by testing against 3 and
+adding Fizz to a buffer. Then test against 5 and if appropriate append
+Buzz to the buffer. Either the buffer was empty, in which case you get
+Buzz alone - or it already contained Fizz in which case the buffer now
+contains FizzBuzz. Finally, if *anything* is in the buffer, cause the
+buffer to be printed and append a new line.
+
+In C++, the buffer could be a C++ string or a stringstream. In C
+you might think that you must resort to using an array of `char` to
+act as the buffer, filling it with `strncpy` or some such nonsense.
+
+But you don't have to bother! `printf` is a buffered output stream.
+It won't print anything until it encounters a new line character.
+
+In this program, we'll use this to buffer up either Fizz, Buzz or
+both then as indicated above, we'll end with a new line and BAM -
+whatever was in the `printf` buffer gets sent to the console.
+
+[Here is a video](https://youtu.be/aJSGTIxu4ik) where we walk through
+the process of writing FizzBuzz from scratch in ARM 64 bit assembly
+language.
+
+[Here is the source code](./fizzbuzz.s).
+
+The video is long but there is much benefit to be had by watching
+and listening to another person's process as they write the code.
+**AND especially** listening and watching to them debug when 
+things go wrong!

section_1/fizzbuzz/fizzbuzz.s

@@ -1,91 +1,93 @@
-/*		Perry Kivolowitz
+	    .global	main
-		CSC3510
+        .text
-*/
+        .align	2
-		.global	main
-		.text
-		.align	2
 
 /*	FizzBuzz - a classic interview question.
 
-	Count from 0 to n (let's make it 100).
+    Count from 0 to n (let's make it 100).
-	If the value is divisible by 3, print Fizz
+    If the value is divisible by 3, print Fizz
-	If the value is divisible by 5, print Buzz
+    If the value is divisible by 5, print Buzz
-	If the value is divisible by both 3 and 5, print FizzBuzz
+    If the value is divisible by both 3 and 5, print FizzBuzz
-	Otherwise, print the number.
+    Otherwise, print the number.
 */
 
 /*	Bible:
 
-	x20		counter
+    x20		counter
-	w21		bool that says whether or not I have printed anything
+    w21		bool that says whether or not I have printed anything
 */
 
 /*	mod(a, b) - implements a % b
-	integer divide a by b - for example - 5 % 3 would need 5 // 3 yielding 1
+	a comes to us in x0
-	multiply result by b - 1 * 3 is 3
+	b comes to us in x1
-	subtract result from a - 5 - 3 yielding 2 and that's our return value.
+	method:
+    integer divide a by b - for example - 5 % 3 
+	    would need 5 // 3 yielding 1
+    multiply result by b - 1 * 3 is 3
+    subtract result from a - 5 - 3 yielding 2 
+	    and that's our return value.
 */
 mod:	sdiv 	x2, x0, x1				// x2 gets a // b
-		msub	x0, x2, x1, x0			// x0 gets a - a // b * b 	
+        msub	x0, x2, x1, x0			// x0 gets a - a // b * b	
-		ret
+        ret
 
 main:	stp		x20, x30, [sp, -16]!
-		str		x21, [sp, -16]!
+        str		x21, [sp, -16]!
 
-		mov		x20, xzr
+        mov		x20, xzr
 1:		cmp		x20, 100
-		bge		99f
+        bge		99f
 
-		mov		w21, wzr
+        mov		w21, wzr
 
-		// Test for divisible by 3
+        // Test for divisible by 3
-		mov		x0, x20
+        mov		x0, x20
-		mov		x1, 3
+        mov		x1, 3
-		bl		mod
+        bl		mod
-		cbnz	x0, 5f
+        cbnz	x0, 5f
-		// If we get here, the counter was divisible by 3
+        // If we get here, the counter was divisible by 3
-		ldr		x0, =fizz
+        ldr		x0, =fizz
-		bl		printf
+        bl		printf
-		add		w21, w21, 1
+        add		w21, w21, 1
 
 5:		mov		x0, x20
-		mov		x1, 5
+        mov		x1, 5
-		bl		mod
+        bl		mod
-		cbnz	x0, 10f
+        cbnz	x0, 10f
-		// If we get here, the counter was divisible by 5
+        // If we get here, the counter was divisible by 5
-		ldr		x0, =buzz
+        ldr		x0, =buzz
-		bl		printf
+        bl		printf
-		add		w21, w21, 1
+        add		w21, w21, 1
 
 10:		cbz 	w21, 20f
-		// If we get here, it means that we have printed
+        // If we get here, it means that we have printed
-		// something (either fizz, or buzz or fizzbuzz)
+        // something (either fizz, or buzz or fizzbuzz)
-		// so all we need now is a new line
+        // so all we need now is a new line
-		ldr		x0, =nl
+        ldr		x0, =nl
-		bl		puts
+        bl		puts
-		b 		80f
+        b 		80f
 
 20:		// If we get here, the counter was neither a
-		// multiple of 3 nor of 5. Therefore, we need
+        // multiple of 3 nor of 5. Therefore, we need
-		// to print the counter itself.
+        // to print the counter itself.
 
- 		ldr		x0, =fmt
+        ldr		x0, =fmt
-		mov		x1, x20
+        mov		x1, x20
-		bl 		printf
+        bl 		printf
 
 80:		add		x20, x20, 1
-		b 		1b		
+        b 		1b		
 
 
 99:		ldr		x21, [sp], 16
-		ldp		x20, x30, [sp], 16
+        ldp		x20, x30, [sp], 16
-		mov		w0, wzr
+        mov		w0, wzr
-		ret
+        ret
 
-		.data
+        .data
 fizz:	.asciz	"Fizz"
 buzz:	.asciz	"Buzz"
 nl:		.asciz	""
 fmt:	.asciz	"%ld\n"
 
-		.end
+        .end