/*******************************************************
*         File:  ArrayOfStruct.m
*         Date:  Oct. 31, 2021
*       Author:  DSS
*     Computer:  KUNET suns
*      Execute:  ArrayOfStruct
*      Purpose:  to demonstrate the use of arrays as allocated on the stack. 
*      		  This example shows an array of struct
*		 It illustrates how components of the arrays are referenced 
*		 Also, the nuances of alignment come into play
*		 efficiently and demonstrates offsets via an index search
*
*		 This program will define an array (size 10) of struct stored 
*		 in the stack and use a for loop to read in *up to* ten values 
*		 and then print them out.
*
*******************************************************/

define(name,0)		# 20 char string
define(age,20)		# 32-bit int
define(level,24)	# char representing class '1'=fr '2'=so, etc.
define(student,28)	# 28 bytes/student (why, when only 25 used?)
define(List,288)	# Space required for the array
define(count,%r14)	# Counter register
define(index,%r15)
define(eltAdrs,%r13)	# Register used to keep track of where to store fields

.global main

main:
	push 	%rbp           		# keep stack aligned
	# Make room for 10 ints on the stack
	subq	$List, %rsp		# must also remain divisible by 16
	movq	$0, count		# Count # elts
loop:
	# Next record offset must be found
	movq	%rsp, eltAdrs		# Base address is the stack pointer
	movq	$student, %rax
	mulq	count			# %rax now holds offset to this elt
	addq	%rax, eltAdrs		# Read into eltAdrs+offset
	# Prompt for name
	leaq 	getName(%rip), %rdi  	# load format string to proper register
	call    printf          	# print it
	# Read the name
	# leaq 	fmt_in(%rip), %rdi  	# load format string
	movq	eltAdrs, %rdi
	addq	$name, %rdi		# Offset to name
	call 	gets			# Read the name
	# Did they enter ^D (eotext)? gets returns null on ^D
	cmp	$0,%rax			
	je	print			# If equal, time to print

	# Prompt for age
	leaq 	getAge(%rip), %rdi  	# load format string for age prompt
	call    printf          	# print it
        # Read it
	leaq 	int_in(%rip), %rdi  	# load format string for int
	movq	eltAdrs, %rsi
	addq	$age, %rsi		# Offset to name
	call 	scanf

	# Prompt for level
	leaq 	getClass(%rip), %rdi  	# load format string for age prompt
	call    printf          	# print it
        # Read it
	leaq 	char_in(%rip), %rdi  	# load format string for int
	movq	eltAdrs, %rsi
	addq	$level, %rsi		# Offset to level
	movq	%rsi, %rdx		# What's going on? Five arguments?
	movq	%rdx, %rcx		# How does it work? Why three chars?
	addq	$2,%rcx			
	call 	scanf

	# Check if 10 elements read
	inc	count			# Counter up
#	cmp	$10,count 		# If equal, time to exit
	cmp	$4,count 		# If equal, time to exit
	jz	print

	jmp	loop			# If you get here, go get next value
	dec	count

	# xor	eltAdrs,eltAdrs
print:
	# Print Header
	leaq 	header(%rip), %rdi  	# load format string for age prompt
	call    printf          	# print it
	
	movq	%rsp, eltAdrs		# Base address is the stack pointer
	movq	$0, index		# #elts is in count, %r15 is now counting
printLoop:
	leaq	output(%rip),%rdi	# Output format set to 1st argument
	movq	eltAdrs,%rsi
	addq	$name, %rsi		# Offset to name
	movq	eltAdrs,%rdx
	addq	$age, %rdx		# Address of age in %rdx
	movq	(%rdx),%rdx		# age is now in %rdx
	movq	eltAdrs,%rcx
	addq 	$level, %rcx		# Address of level in %rcx
	movq	(%rcx),%rcx		# level is now in %rcx
	call	printf

	#inc eltAdrs to next elt
	addq	$student,eltAdrs
	
	# Are we done?
	inc	index			# Inc counter
	cmp	count,index		# Equal to # elts?
	jl	printLoop			# No? Print next value

done:
	addq	$List, %rsp		# Deallocate the array (not critical)
	pop	%rbp
	ret

.data
getName:	.asciz	"Enter Name: "
getAge:		.asciz	"Enter Age: "
getClass:	.asciz	"Enter Class 1)Frosh 2)Soph 3)Jr 4)Sr   >"
int_in:		.asciz	"%d"
char_in:	.asciz	"%c%c%c"
output:		.asciz	"Name: %16s  Age: %4d  Class: %2c\n"
header:		.asciz	"\nPeople Entered\n"