first effort on recursion - not anywhere done

section_1/recursion/a.out.dSYM/Contents/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+	<dict>
+		<key>CFBundleDevelopmentRegion</key>
+		<string>English</string>
+		<key>CFBundleIdentifier</key>
+		<string>com.apple.xcode.dsym.a.out</string>
+		<key>CFBundleInfoDictionaryVersion</key>
+		<string>6.0</string>
+		<key>CFBundlePackageType</key>
+		<string>dSYM</string>
+		<key>CFBundleSignature</key>
+		<string>????</string>
+		<key>CFBundleShortVersionString</key>
+		<string>1.0</string>
+		<key>CFBundleVersion</key>
+		<string>1</string>
+	</dict>
+</plist>

section_1/recursion/fib.c

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+#include <stdio.h>
+
+extern unsigned int Fib(unsigned int nthNumber);
+
+unsigned int FibonacciInC(unsigned int nthNumber) {
+	if (nthNumber <= 1) {
+		return nthNumber;
+	}
+	return FibonacciInC(nthNumber - 1) + FibonacciInC(nthNumber - 2);
+}
+
+int main() {
+	printf("In C:\n");
+	for (unsigned int n = 0; n < 10; n++) {
+		printf("Fibonacci number %2d is: %d\n", n, FibonacciInC(n));
+	}
+	printf("In assembly language:\n");
+	for (unsigned int n = 0; n < 10; n++) {
+		printf("Fibonacci number %2d is: %d\n", n, Fib(n));
+	}
+	return 0;
+}

section_1/recursion/fib.s

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+	.arch armv8-a
+	.file	"fib.c"
+	.text
+	.align	2
+	.global	FibonacciInC
+	.type	FibonacciInC, %function
+FibonacciInC:
+.LFB0:
+	.cfi_startproc
+	stp	x29, x30, [sp, -48]!
+	.cfi_def_cfa_offset 48
+	.cfi_offset 29, -48
+	.cfi_offset 30, -40
+	mov	x29, sp
+	str	x19, [sp, 16]
+	.cfi_offset 19, -32
+	str	w0, [sp, 44]
+	ldr	w0, [sp, 44]
+	cmp	w0, 1
+	bhi	.L2
+	ldr	w0, [sp, 44]
+	b	.L3
+.L2:
+	ldr	w0, [sp, 44]
+	sub	w0, w0, #1
+	bl	FibonacciInC
+	mov	w19, w0
+	ldr	w0, [sp, 44]
+	sub	w0, w0, #2
+	bl	FibonacciInC
+	add	w0, w19, w0
+.L3:
+	ldr	x19, [sp, 16]
+	ldp	x29, x30, [sp], 48
+	.cfi_restore 30
+	.cfi_restore 29
+	.cfi_restore 19
+	.cfi_def_cfa_offset 0
+	ret
+	.cfi_endproc
+.LFE0:
+	.size	FibonacciInC, .-FibonacciInC
+	.section	.rodata
+	.align	3
+.LC0:
+	.string	"In C:"
+	.align	3
+.LC1:
+	.string	"Fibonacci number %2d is: %d\n"
+	.align	3
+.LC2:
+	.string	"In assembly language:"
+	.text
+	.align	2
+	.global	main
+	.type	main, %function
+main:
+.LFB1:
+	.cfi_startproc
+	stp	x29, x30, [sp, -32]!
+	.cfi_def_cfa_offset 32
+	.cfi_offset 29, -32
+	.cfi_offset 30, -24
+	mov	x29, sp
+	adrp	x0, .LC0
+	add	x0, x0, :lo12:.LC0
+	bl	puts
+	str	wzr, [sp, 24]
+	b	.L5
+.L6:
+	ldr	w0, [sp, 24]
+	bl	FibonacciInC
+	mov	w2, w0
+	ldr	w1, [sp, 24]
+	adrp	x0, .LC1
+	add	x0, x0, :lo12:.LC1
+	bl	printf
+	ldr	w0, [sp, 24]
+	add	w0, w0, 1
+	str	w0, [sp, 24]
+.L5:
+	ldr	w0, [sp, 24]
+	cmp	w0, 9
+	bls	.L6
+	adrp	x0, .LC2
+	add	x0, x0, :lo12:.LC2
+	bl	puts
+	str	wzr, [sp, 28]
+	b	.L7
+.L8:
+	ldr	w0, [sp, 28]
+	bl	Fib
+	mov	w2, w0
+	ldr	w1, [sp, 28]
+	adrp	x0, .LC1
+	add	x0, x0, :lo12:.LC1
+	bl	printf
+	ldr	w0, [sp, 28]
+	add	w0, w0, 1
+	str	w0, [sp, 28]
+.L7:
+	ldr	w0, [sp, 28]
+	cmp	w0, 9
+	bls	.L8
+	mov	w0, 0
+	ldp	x29, x30, [sp], 32
+	.cfi_restore 30
+	.cfi_restore 29
+	.cfi_def_cfa_offset 0
+	ret
+	.cfi_endproc
+.LFE1:
+	.size	main, .-main
+	.ident	"GCC: (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0"
+	.section	.note.GNU-stack,"",@progbits

section_1/recursion/fibo.s

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+		.global	Fib
+		.text
+		.align	4
+
+Fib:	str		x30, [sp, -16]!
+		cmp		w0, 1
+		// If w0 is 0 or 1, take the branch to return w0.
+		bls		99f
+
+		// If we get here, we need to do the recursion.
+		// Save the parameter on the stack so we can
+		// get it back between recursions.
+
+		str		w0, [sp, -16]!
+		sub		w0, w0, 1
+		bl		Fib
+		ldr		w0, [sp], 16	// temporary
+		
+99:		ldr		x30, [sp], 16
+		ret
+