/*******************************************************
*         File:  StructEx.m           
*         Date:  Oct. 31, 2021
*       Author:  DSS
*     Computer:  KUNET suns
*      Execute:  StructEx1
*      Purpose:  to demonstrate the use of structs as allocated on the stack. 
*		 It illustrates how components of the structs are referenced 
*		 efficiently and demonstrates offsets via an index search
*
*		 This program will define a struct stored in the stack
*		 read in its fields and print them out.
*
*		 It uses minimal code, optimizing several things
*******************************************************/
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,32)


.global main

main:
	push 	%rbp           		# keep stack aligned
	subq	$student,%rsp		# Make room for a student
	# Make room for 10 ints on the stack
loop:
	# 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	%rsp, %rdi
	addq	$name, %rdi		# Offset to name
	call 	gets			# Read the name

	# 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	%rsp, %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	%rsp, %rsi
	addq	$level, %rsi		# Offset to level
	movq	%rsi, %rdx		# What's going on? Four arguments?
					#  Comment previous line to find out
	call 	scanf

print:	# Print the struct
	leaq	output(%rip),%rdi
	movq	%rsp,  %rsi		# Struct starts at stack pointer
	addq	$name, %rsi		# Offset to name; adrs to register
	movq	0x14(%rsi),%rdx  	# Load age... 20 bytes past %rsp
	movq	0x18(%rsi), %rcx	# Level is 24 bytes past %rsp
	call printf			# Note level's value is loaded
	
done:
	addq	$student, %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"
output:		.asciz	"Name: %s  Age: %d  Class: %c\n"