init

src/lib.asm

@@ -0,0 +1,116 @@
+; ***************************
+; slen : String -> Int
+; calculates length of string
+; ***************************
+
+slen:
+  push ebx
+  mov ebx, eax
+
+slen_nextchar:
+  cmp byte [eax], 0
+  jz slen_finished
+  inc eax
+  jmp slen_nextchar
+
+slen_finished:
+  sub eax, ebx
+  pop ebx
+  ret
+
+; *********************
+; clear_bss : BSS -> IO
+; clears memory block
+; *********************
+
+clear_bss:
+  cmp byte [eax], 0
+  jz clear_bss_finished
+  mov [eax], byte 0
+  inc eax
+  jmp clear_bss
+
+clear_bss_finished:
+  ret
+
+; *******************************
+; scmp : String -> String -> Bool
+; compares 2 strings exactly
+; *******************************
+
+scmp:
+  push ecx
+
+scmp_nextchar:
+  mov cl, byte [ebx]
+  cmp byte [eax], cl
+  jnz scmp_bad
+  cmp byte [eax], 0
+  jz scmp_good
+  inc eax
+  inc ebx
+  jmp scmp_nextchar
+
+scmp_good:
+  mov eax, 0
+  jmp scmp_finished
+
+scmp_bad:
+  mov eax, 1
+
+scmp_finished:
+  pop ecx
+  ret
+
+; *********************
+; sprint : String -> IO
+; prints string
+; *********************
+
+sprint:
+  push edx
+  push ecx
+  push ebx
+  push eax
+  call slen
+
+  mov edx, eax
+  pop eax
+  mov ecx, eax
+  mov ebx, 1
+  mov eax, 4
+  int 80h
+
+  pop ebx
+  pop ecx
+  pop edx
+  ret
+
+; ***********************
+; sprintln : String -> IO
+; prints string + 0Ah
+; ***********************
+
+sprintln:
+  call sprint
+  push eax    ; initial
+
+  mov eax, 0Ah
+  push eax     ; linefeed
+  mov eax, esp ; esp is stack pointer
+  call sprint
+
+  pop eax ; linefeed
+  pop eax ; initial
+  ret
+
+; ************
+; exit : IO
+; exit program
+; ************
+
+exit:
+  mov ebx, 0
+  mov eax, 1
+  int 80h
+  ret

src/main.asm

@@ -0,0 +1,61 @@
+%include 'lib.asm'
+
+SECTION .data
+welcome_message db 'Welcome to this test program! It is experimental and very subject to change.', 0h
+prompt          db 'Enter a string to print: ', 0h
+exit_str        db 'exit', 0Ah, 0h
+
+SECTION .bss
+; resb ; 0001 byte
+; resw ; 0010 word
+; resd ; 0100 double word
+; resq ; 1000 quad word
+; rest ; 1010 ten bytes
+sinput: resb 255 ; 255 bytes
+
+SECTION .text
+global _start
+
+_start:
+  pop ecx ; number of arguments
+
+  pop eax ; dispose of first value, the exe
+  dec ecx
+
+  mov eax, welcome_message
+  call sprintln
+
+next_arg:
+  cmp ecx, 0h
+  jz prompt_loop
+  pop eax
+  call sprintln
+  dec ecx
+  jmp next_arg
+
+prompt_loop:
+  mov eax, prompt
+  call sprint
+
+  mov eax, sinput
+  call clear_bss
+
+  mov edx, 255    ; max bytes to read
+  mov ecx, sinput ; buffer
+  mov ebx, 0      ; (STDIN) where to read from
+  mov eax, 3      ; (SYS_READ)
+  int 80h
+
+  mov eax, sinput
+  mov ebx, exit_str
+  call scmp
+  cmp byte eax, 0
+  jz done
+
+  mov eax, sinput
+  call sprint
+
+  jmp prompt_loop
+
+done:
+  call exit