Move vram functions into separate file

x86_vram_functions.asm

@@ -0,0 +1,55 @@
+%include "x86_vram.asm"
+
+; first argument is row, 1 byte
+; second argument is column, 1 byte
+; third argument is cell, 2 bytes
+write_to_coord:
+    push ebp
+    mov ebp, esp
+    push edi
+    push ebx
+
+    ; should do the same thing
+    ;call get_vram_offset
+    ;mov edi, eax
+    mov edi, X86_VRAM
+    mov ebx, [ebp+8]
+    imul ebx, X86_COLS*2
+    add ebx, [ebp+12]
+    add ebx, [ebp+12]
+    add edi, ebx ;edi now has effective address
+
+    mov ebx, [ebp+16] ;; load word into ebx
+    mov [edi], bx
+
+    pop ebx
+    pop edi
+    mov esp, ebp
+    pop ebp
+    ret
+
+; takes character/attribute in edi
+; writes it to all cells on screen
+clear:
+    push ebp
+    mov ebp, esp
+    push edi
+
+    ; movzx - move and zero-extend
+    ; this trick lets us write half as many doublewords to vram
+    movzx eax, word [ebp + 8]
+    mov edx, eax
+    shl eax, 16
+    or eax, edx
+
+    ; stosd stores eax at the address in edi (here, vram)
+    ; and then increments edi
+    ; rep stosd  repeats stosd while ecx is nonzero
+    mov edi, X86_VRAM
+    mov ecx, X86_COLS * X86_ROWS / 2
+    rep stosd ; "A REP STOS instruction is the fastest way to initialize a large block of memory."
+
+    pop edi
+    mov esp, ebp
+    pop ebp
+    ret