Add hexadecimal dump function

The function which is added with this commit writes a caller-supplied
hexadecimal string of a caller-supplied length to the display, nibble
by nibble, leaving the background black and making the text white.

i386/loader/src-asm/utility/display.asm

@@ -0,0 +1,106 @@
+
+FRAMEBUFFER_ADDRESS equ 0xb8000
+
+; Arguments:
+;   [FURTHEST FROM EBP]
+;     4. U32            Target Y-Position
+;     3. U32            Target X-Position
+;     2. U32            Length of Hexadecimal String
+;     1. Ptr32          Hexadecimal String
+;   [NEAREST TO EBP]
+write_hexadecimal_string:
+    push        dword                   esi
+    sub         esp,                    64
+    mov         esi,                    esp
+
+    mov         [esi + (64 - 4)],       eax
+    mov         [esi + (64 - 8)],       ebx
+    mov         [esi + (64 - 12)],      ecx
+    mov         [esi + (64 - 16)],      edx
+    mov         [esi + (64 - 20)],      edi
+
+    ; [esi]:    
+
+.initialize_writer_loop:
+    xor         ecx,                    ecx
+
+.writer_loop:
+    cmp ecx, [ebp - 8]
+    jae .epilog
+
+    ; Calculate the byte's start on-screen (A single byte from
+    ; the input uses 6 bytes in the framebuffer as every single
+    ; character uses 2 bytes and there are 3 characters per byte
+    ; written; the upper nibble, the lower nibble and the padding.
+
+    ; Multiply the row with 80, the number of cells per row
+    mov eax, [ebp - 16]
+    mov edx, 80
+    mul edx
+
+    ; Add the offset within the row ontop
+    add eax, [ebp - 12]
+    add eax, ecx
+
+    ; Multiply with 2 to get the byte offset
+    ; from the character index
+    mov edx, 6
+    mul edx
+
+    ; Point into the framebuffer
+    add eax, FRAMEBUFFER_ADDRESS
+
+    ; Save the value
+    mov [esi], eax
+
+.write_upper_nibble:
+    ; Lookup the hexadecimal character
+    xor eax, eax
+    mov ebx, [ebp - 4]
+    add ebx, ecx
+    mov al, [ebx]
+    shr al, 4
+    mov ebx, .hexadecimal_lookup
+    add ebx, eax
+    mov dl, [ebx]
+
+    mov ebx, [esi]
+    mov [ebx], dl
+    ; Set the color code for leaving the background black (0x0?)
+    ; and making the foreground be white (0x?f).
+    mov [ebx + 1], byte 0x0f
+
+.write_lower_nibble:
+    ; Lookup the hexadecimal character
+    xor eax, eax
+    mov ebx, [ebp - 4]
+    add ebx, ecx
+    mov al, [ebx]
+    and al, 0x0f
+    mov ebx, .hexadecimal_lookup
+    add ebx, eax
+    mov dl, [ebx]
+
+    mov ebx, [esi]
+    mov [ebx + 2], dl
+    ; Set the color code for leaving the background black (0x0?)
+    ; and making the foreground be white (0x?f).
+    mov [ebx + 3], byte 0x0f
+
+
+    inc ecx
+    jmp .writer_loop
+
+.epilog:
+    mov         eax,                    [esi + (64 - 4)]
+    mov         ebx,                    [esi + (64 - 8)]
+    mov         ecx,                    [esi + (64 - 12)]
+    mov         edx,                    [esi + (64 - 16)]
+    mov         edi,                    [esi + (64 - 20)]
+
+    add         esp,                    64
+    pop         dword esi
+    ret
+
+.hexadecimal_lookup:
+    db "0123456789abcdef"