From 6a037ea2ece5ef8436723ce130e2ca980d519b29 Mon Sep 17 00:00:00 2001
From: Tijmen van Nesselrooij <tijmen_222@hotmail.com>
Date: Fri, 15 Mar 2019 19:54:33 +0100
Subject: [PATCH] Jump added

---
 x86_64/3_homework.asm |  34 ++++++++++++
 x86_64/3_jump.asm     | 118 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 152 insertions(+)
 create mode 100644 x86_64/3_homework.asm
 create mode 100644 x86_64/3_jump.asm

diff --git a/x86_64/3_homework.asm b/x86_64/3_homework.asm
new file mode 100644
index 0000000..8e6bc73
--- /dev/null
+++ b/x86_64/3_homework.asm
@@ -0,0 +1,34 @@
+global _start
+
+; Program that finds the highest number in the byte array declared below
+
+section .data
+  data: db 0, 15, 57, 2, 43, 87, 2
+  dataSize: equ 7
+
+section .bss
+
+section .text
+_start:
+  xor rbx, rbx
+  xor rcx, rcx
+  mov rax, 1 ; iterator value
+  mov cl, byte [data] ; default value for the result
+
+loop_start:
+  cmp rax, dataSize
+  jge loop_end
+
+  mov bl, byte [rax + data] ; load next candidate
+  cmp cl, bl   ; compare to (default) value
+  jge loop_inc ; skip if cl >= bl
+  mov cl, bl   ; set higher value
+
+loop_inc:
+  inc rax
+  jmp loop_start
+
+loop_end:
+  mov rax, 60
+  mov rdi, rcx ; return the highest number as exit code
+  syscall
diff --git a/x86_64/3_jump.asm b/x86_64/3_jump.asm
new file mode 100644
index 0000000..98df487
--- /dev/null
+++ b/x86_64/3_jump.asm
@@ -0,0 +1,118 @@
+global _start
+
+; Static data
+section .data
+	promptStr: db 'Write something! (max 32 bytes)',0xA
+	promptStrSize: equ $ - promptStr
+
+	unusedStr: db "This string won't be printed",0xA
+	unusedStrSize: equ $ - unusedStr
+
+	lessStr: db 'The input string has less than 16 bytes',0xA
+	lessStrSize: equ $ - lessStr
+
+	moreStr: db 'The input string has 16 bytes or more',0xA
+	moreStrSize: equ $ - moreStr
+
+; Dynamic data
+section .bss
+  inputBuffer: resb 32
+  inputBufferSize: equ 32
+
+; Code
+section .text
+_start:
+  mov rax, 1
+  mov rdi, 1 ; stdout
+  mov rsi, promptStr
+  mov rdx, promptStrSize
+  syscall
+
+  jmp request_input
+
+  ; Skipped over
+  mov rax, 1
+  mov rdi, 1
+  mov rsi, unusedStr
+  mov rdx, unusedStrSize
+  syscall
+
+request_input:
+  xor rax, rax ; 0 = read
+  xor rdi, rdi ; 0 = stdin
+  mov rsi, inputBuffer
+  mov rdx, inputBufferSize
+  syscall
+
+  mov rbx, rax ; store read bytes
+
+  ; *** FLAGS *** (16 bit era)
+  ; Bit  Abbreviation Description
+  ; 0    CF           Carry Flag  (1 = carry, 0 = no carry)
+  ; 2    PF           Parity Flag (1 = even, 0 = uneven)
+  ; 4    AF           Adjust Flag (1 = auxiliary carry, 0 no ...)
+  ; 6    ZF           Zero Flag   (1 = zero, 0 = non zero)
+  ; 7    SF           Sign Flag   (1 = negative, 0 = positive)
+  ; 8    TF           Trap Flag
+  ; 9    IF           Interrupt Flag (1 = enabled, 0 = disabled)
+  ; 10   DF           Direction Flag (1 = down, 0 = up)
+  ; 11   OF           Overflow Flag  (1 = overflow, 0 = no overflow)
+  ; 12 --v  
+  ; 13   IOPL         IO Privilege Level
+  ; 14   NT           Nested Task
+  ; 
+  ; *** EFLAGS *** (32 bit era)
+  ; 16   RF           Resume Flag
+  ; 17   VM           Virtual 8086 mode
+  ; 18   AC           Alignment check
+  ; 19   VIF          Virtual Interrupt Flag
+  ; 20   VIP          Virtual Interrupt Pending
+  ; 21   ID           CPUID enabled flag
+  ;
+  ; *** RFLAGS *** (64 bit era)
+  ; -    -            None yet
+
+  ; Subtraction without storing the result
+  cmp rbx, 16
+  ; Jump based upon the flags set above
+  jl less_than_16
+
+  ; >= 16 bytes
+  mov rax, 1
+  mov rdi, 1
+  mov rsi, moreStr
+  mov rdx, moreStrSize
+  syscall
+
+  jmp size_printed
+
+less_than_16:
+  mov rax, 1
+  mov rdi, 1
+  mov rsi, lessStr
+  mov rdx, lessStrSize
+  syscall
+
+size_printed:
+  dec rbx ; subtract the newline from the count
+  
+  xor rcx, rcx ; loop variable
+loop_begin:
+  cmp rcx, rbx ; while loop var < (string size - 1)
+  jge loop_end
+  inc byte [inputBuffer + rcx]
+  inc rcx
+  jmp loop_begin
+
+loop_end:
+  inc rbx ; restore original bytes read count
+
+  mov rax, 1
+  mov rdi, 1
+  mov rsi, inputBuffer
+  mov rdx, rbx
+  syscall
+
+  mov rax, 60
+  xor rdi, rdi
+  syscall ; see ya