From 80088628a2302ef455049236425014c4acee9341 Mon Sep 17 00:00:00 2001
From: robert <rpe2101@gmail.com>
Date: Mon, 11 Mar 2024 18:14:41 -0500
Subject: [PATCH 1/2] Changes to be committed: new file:   fib3.S

---
 Fibonacci/fib3.S | 116 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 Fibonacci/fib3.S

diff --git a/Fibonacci/fib3.S b/Fibonacci/fib3.S
new file mode 100644
index 0000000..ad7f364
--- /dev/null
+++ b/Fibonacci/fib3.S
@@ -0,0 +1,116 @@
+.file "fib3.S"
+.section .note.GNU-stack
+.extern printf, atoi, calloc, free
+
+//
+//  Expected Compile Command: gcc -o fib3 fib3.S
+//
+//  Purpose: Print the n'th fibonacci term to standard output
+//  Usage: ./fib3 n
+//
+//         n = Fibinacci term to output\n"
+//
+
+
+.data
+.section .rodata
+
+format_str_result: .asciz "Fibonacci Number: %llu\n"
+usage_txt: .asciz "Usage: ./fib3 n \n\n\
+      n = Fibinacci term to output\n\n"
+
+.text
+
+start_fib: // %rsi = fibanocci_sequence ( %rsi'th term) BORKS %rdi, %rcx, %rdx
+	// Base case: if n<=1, return n
+	cmp $1, %rsi
+	jle end_fib	
+
+	// Get enough memory to cover the fib sequence with calloc
+	movq $8, %rdi
+	push %rsi
+	inc %rsi    // Need n+1 memory, because there's a 0th term needing accounting for.
+	call calloc // %rax = calloc( %rdi, %rsi)
+	pop %rsi
+
+	// Check if calloc Failed
+	cmp $0, %rax
+	jle exit
+
+	// Save calloc location a little out of way for indirect addressing.
+	movq %rax, %rdx
+
+	// Populate initial values
+	movq $0, (%rax)
+	movq $1, 8(%rax)
+	movq $2, %rcx
+
+fib_iterate: 
+	// fib (n) = fib(n-1) + fib(n-2)
+	// 	Counter %rcx starts at 2 until desired n.
+	// 	Iterate until desired n (%rsi).
+	//	%rax is a moving pointer for reading prior sequence locations in the heap.
+	//	(%rdx,%rcx,8) is indirect address to fib(n)
+
+	// Copy fib(n-2) -> fib(n)
+	movq (%rax), %rdi
+	movq %rdi, (%rdx,%rcx,8)
+	add $8, %rax
+
+	// Add fib (n-1) to fib(n-2) at fib(n) locaton.
+	movq (%rax), %rdi
+	add %rdi, (%rdx,%rcx,8)
+
+	//Check that counter is less than ultimate desired, and if so iterate.
+	//If allowed to increment past, there will be no memory there.
+	cmp %rsi, %rcx
+	jge fib_finalize
+
+	//Iterate.
+	inc %rcx
+	jmp fib_iterate
+
+fib_finalize:
+	pushq (%rdx,%rcx,8) // Save the result
+	movq %rdx, %rdi
+	call free
+	popq %rsi //Put result in expected location
+
+end_fib:
+	ret
+
+
+print_fib: 
+	xorq %rax, %rax //Cause the internet said you had to.
+	leaq format_str_result(%rip), %rdi
+	call printf     // printf( %rdi, %rsi)
+	ret
+
+usage_msg:
+	xorq %rax, %rax //Cause the internet said you had to.
+	leaq usage_txt(%rip), %rdi
+	call printf
+	jmp exit
+
+.global main
+main:
+	//Expecting 2 arguments, otherwise exit.
+	cmpq $2, %rdi  //Check if argc is correct
+	jne usage_msg
+
+	//Convert argument string to integer
+	addq $8, %rsi //argv[1]
+	movq (%rsi), %rdi // Load address of argv[1]
+	call atoi // %rax = atoi(  (char*)%rdi )
+
+	//Run Fibonacci algorithm
+	movq %rax, %rsi
+	call start_fib  // fibonacci('n' = %rsi)
+	
+	call print_fib
+
+exit:
+	mov $231, %rax
+	mov $0, %rsi
+	syscall
+

From 8576a3a80ae54e9e90d570f90fcb5be83d7c7d88 Mon Sep 17 00:00:00 2001
From: robert <rpe2101@gmail.com>
Date: Mon, 11 Mar 2024 18:32:58 -0500
Subject: [PATCH 2/2] Changes for clarity.  Added code for case of a negative
 number.

 Changes to be committed:
	modified:   fib3.S
---
 Fibonacci/fib3.S | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/Fibonacci/fib3.S b/Fibonacci/fib3.S
index ad7f364..f4ed624 100644
--- a/Fibonacci/fib3.S
+++ b/Fibonacci/fib3.S
@@ -5,6 +5,8 @@
 //
 //  Expected Compile Command: gcc -o fib3 fib3.S
 //
+//  Program Enty: main
+//
 //  Purpose: Print the n'th fibonacci term to standard output
 //  Usage: ./fib3 n
 //
@@ -17,11 +19,11 @@
 
 format_str_result: .asciz "Fibonacci Number: %llu\n"
 usage_txt: .asciz "Usage: ./fib3 n \n\n\
-      n = Fibinacci term to output\n\n"
+      n = Fibonacci term to output.  Must be positive number.\n\n"
 
 .text
 
-start_fib: // %rsi = fibanocci_sequence ( %rsi'th term) BORKS %rdi, %rcx, %rdx
+fibonacci: // %rsi = fibanocci_sequence ( %rsi'th term) BORKS %rdi, %rcx, %rdx
 	// Base case: if n<=1, return n
 	cmp $1, %rsi
 	jle end_fib	
@@ -45,7 +47,7 @@ start_fib: // %rsi = fibanocci_sequence ( %rsi'th term) BORKS %rdi, %rcx, %rdx
 	movq $1, 8(%rax)
 	movq $2, %rcx
 
-fib_iterate: 
+fib_loop: 
 	// fib (n) = fib(n-1) + fib(n-2)
 	// 	Counter %rcx starts at 2 until desired n.
 	// 	Iterate until desired n (%rsi).
@@ -68,12 +70,12 @@ fib_iterate:
 
 	//Iterate.
 	inc %rcx
-	jmp fib_iterate
+	jmp fib_loop
 
 fib_finalize:
 	pushq (%rdx,%rcx,8) // Save the result
 	movq %rdx, %rdi
-	call free
+	call free  // ***  See!?  ***
 	popq %rsi //Put result in expected location
 
 end_fib:
@@ -87,7 +89,7 @@ print_fib:
 	ret
 
 usage_msg:
-	xorq %rax, %rax //Cause the internet said you had to.
+	xorq %rax, %rax
 	leaq usage_txt(%rip), %rdi
 	call printf
 	jmp exit
@@ -105,12 +107,14 @@ main:
 
 	//Run Fibonacci algorithm
 	movq %rax, %rsi
-	call start_fib  // fibonacci('n' = %rsi)
+	cmp $0, %rsi
+	jl usage_msg
+
+	call fibonacci  // fibonacci('n' = %rsi)
 	
-	call print_fib
+	call print_fib  // Output the result
 
 exit:
 	mov $231, %rax
 	mov $0, %rsi
 	syscall
-