BASIC interpreter
This commit is contained in:
deadvey
259
source/kernel/features/strings.asm
Executable file → Normal file
259
source/kernel/features/strings.asm
Executable file → Normal file
@@ -1,11 +1,11 @@
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; How string comparison works
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; DI => scasb compares value stored in DI which is 's' with 's' stored in AX register
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; and then increments DI if DF is 0
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; v
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; memory address 1: |s|n|a|t|0|
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; memory address 2: |s|n|a|k|e|0|
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; ^
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; SI => lodsb loads value stored at SI to AX and then increments SI if DF is 0
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; DI => scasb compares value stored in DI which is 's' with 's' stored in AX register
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; and then increments DI if DF is 0
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; v
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; memory address 1: |s|n|a|t|0|
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; memory address 2: |s|n|a|k|e|0|
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; ^
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; SI => lodsb loads value stored at SI to AX and then increments SI if DF is 0
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; Additionaly, if the di string ends and the relevant character in si contains a space, it will still return
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; the strings as being equal, this is to allow for command line arquments
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os_compare_strings:
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@@ -44,22 +44,22 @@ os_compare_strings:
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string_direct_compare:
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pusha
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.more:
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mov al, [si] ; Retrieve string contents
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mov al, [si] ; Retrieve string contents
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mov bl, [di]
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cmp al, bl ; Compare characters at current location
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cmp al, bl ; Compare characters at current location
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jne .not_same
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cmp al, 0 ; End of first string? Must also be end of second
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cmp al, 0 ; End of first string? Must also be end of second
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je .end
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inc si
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inc di
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jmp .more
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.not_same: ; If unequal lengths with same beginning, the byte
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popa ; comparison fails at shortest string terminator
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clc ; Clear carry flag
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.not_same: ; If unequal lengths with same beginning, the byte
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popa ; comparison fails at shortest string terminator
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clc ; Clear carry flag
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ret
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.end: ; Both strings terminated at the same position
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.end: ; Both strings terminated at the same position
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popa
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stc ; Set carry flag
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stc ; Set carry flag
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ret
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@@ -73,8 +73,8 @@ string_copy:
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pusha
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.loop:
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; TODO could this cause issue when a character is > 1 byte?
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lodsb ; Load si character into ax and increment si by 1
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stosb ; Store ax in di location and increment di by 1
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lodsb ; Load si character into ax and increment si by 1
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stosb ; Store ax in di location and increment di by 1
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cmp ax, 0 ; if ax is a 0, quit
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jne .loop
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.done:
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@@ -107,89 +107,84 @@ string_join:
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; ------------------------------------------------------------------------
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; TODO
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; Converts a null terminated string to an integer
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; IN: SI = string location (max 5 chars, up to '65536')
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; OUT: AX = number
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string_cast_to_int:
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ret
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pusha
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xor cx,cx
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.loop:
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xor ax,ax
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lodsb
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cmp al, 0
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je .finish
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sub al, 30h
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mov bx, ax
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mov ax, 10
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mul cx ; Multiple the current value by 10
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add ax, bx ; Then add the new digit
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mov cx, ax
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jmp .loop
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.finish:
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mov [int_tmp], cx
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popa
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mov ax, [int_tmp]
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ret
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; ------------------------------------------------------------------------
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; IN: AX = integer (unsigned)
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; OUT: AX -> null-terminated string
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; IN: AX = int
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; OUT: AX = string location (output buffer)
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string_cast_from_int: ; TODO I think this algorithm could be optimised
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string_cast_from_int:
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pusha
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; Initialise base to decimal (base 10)
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mov bx, 10
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; clear the strigified int location
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mov cx, 6
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push ax
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xor ax,ax
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.clear_loop:
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stosb
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dec cx
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cmp cx, 0
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ja .clear_loop
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; setup
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pop ax
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push ax
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mov cx, -1
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; loop over number to get the value of count (cx)
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.count_loop:
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xor dx,dx
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div bx ; ax = ax // bx
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inc cx
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cmp ax, 0
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ja .count_loop ; Jump if greater
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pop ax
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; loop over count downwards until count is 0
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cld ; Write backwards
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mov di, stringified_int
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.stringify_loop:
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mov cx,1 ;DEL
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push cx
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push bx
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push ax
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; Generate power of 10
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mov ax, 1
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mov cx,0 ;DEL
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cmp cx, 1
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jl .after_power_loop
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.power_loop:
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mul bx
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dec cx
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cmp cx, 0
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ja .power_loop
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.after_power_loop:
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mov bx,ax
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mov bx, 10 ; base
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mov cx, 0 ; digit count
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.convert_loop:
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xor dx, dx
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div bx ; AX = AX / base, DX = remainder
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add dl, '0'
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push dx ; store digit
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inc cx
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test ax, ax
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jnz .convert_loop
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.write_loop:
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pop ax
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pop cx
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; ax = ax DIV bx
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; dx = ax MOD bx
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xor dx,dx
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div bx
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pop bx
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add ax, 30h
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stosb
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mov ax, dx
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dec cx
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cmp cx, 0
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ja .stringify_loop
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.finish:
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loop .write_loop
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mov al, 0
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stosb ; null terminator
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popa
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;mov ax, stringified_int
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mov ax, stringified_int
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ret
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;----------------------------------------------------------------------------
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; Get the length of a string
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; 'hello world', 0 is 11 characters long (excluding the terminator)
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; input: si points to the string to be counted
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; output: cl holds the length
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; input: ax points to the string to be counted
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; output: ax holds the length
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string_length:
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push si
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xor cl,cl ; Clear the al register
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push cx
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mov si, ax
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xor ax,ax ; Clear the cx register
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xor cx,cx
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.loop:
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lodsb
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cmp al, 0
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je .finish
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inc cl
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inc cx
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jmp .loop
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.finish:
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mov ax, cx
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pop cx
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pop si
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ret
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@@ -198,15 +193,17 @@ string_length:
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; convert a string to fat's filename format
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; It will be capitalised and 11 characters long,
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; 8 for the filename, 3 for the extension
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; eg: 'file.txt' -> 'FILE TXT'
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; eg: 'file.txt' -> 'FILE TXT'
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; input: si points to filename, di points to a free 11 bytes in memory
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; output: di points to the fat formatted filename
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os_format_fat_filename:
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pusha
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call string_upper_case
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call string_length ; Stores the length of the string in cl
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xor ch,ch ; Clear ch to reset it to 0
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.character_loop:
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pusha
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call string_upper_case
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mov ax, si
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call string_length ; Stores the length of the string in cl
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mov cl, al
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xor ch,ch ; Clear ch to reset it to 0
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.character_loop:
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lodsb
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cmp al, 0
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je .finish
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@@ -215,10 +212,10 @@ os_format_fat_filename:
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stosb
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inc ch
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jmp .character_loop
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.add_spaces: ; Add the number of spaces as bl holds
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.add_spaces: ; Add the number of spaces as bl holds
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mov al, ' ' ; 20h = space
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; Work out the number of spaces in between
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; the name and extension.
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; 8 - name_length(ch)
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@@ -231,9 +228,9 @@ os_format_fat_filename:
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je .character_loop
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dec bl
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jmp .spaces_loop
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.finish:
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popa
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ret
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.finish:
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popa
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ret
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; Does the inverse of the previous
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; Converts a fat filename back to human readable
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@@ -287,51 +284,53 @@ string_unformat_fat_filename:
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popa
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ret
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; -------------------------------------------------------------------------------------
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; Convert a string to all upper/lower case
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; INPUT: si pointing to a string
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; INPUT: ax pointing to a string
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; OUPUT: the same string in memory will now be capitalised/decapitalised
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string_upper_case: ; to upper case
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pusha
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mov di, si
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pusha
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mov si,ax
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mov di,si
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.loop:
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lodsb ; Load the character into al
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inc di
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cmp al, 0
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je .finish ; If it's null then the string is finished
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cmp al, 7Ah ; 7Ah = 'z'
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jns .loop ; Ignore if it's more than 'z'
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cmp al, 61h ; 61h = 'a'
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js .loop ; Ignore if it's less than 'a'
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sub al, 20h ; Otherwise subtract 20h to capitalise it
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dec di
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stosb ; Store the new value
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jmp .loop ; Next character
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lodsb ; Load the character into al
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inc di
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cmp al, 0
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je .finish ; If it's null then the string is finished
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cmp al, 7Ah ; 7Ah = 'z'
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jns .loop ; Ignore if it's more than 'z'
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cmp al, 61h ; 61h = 'a'
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js .loop ; Ignore if it's less than 'a'
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sub al, 20h ; Otherwise subtract 20h to capitalise it
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dec di
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stosb ; Store the new value
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jmp .loop ; Next character
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.finish:
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popa
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ret
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os_lower_case: ; to lower case
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pusha
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mov di, si
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.loop:
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lodsb ; Load the character into al
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inc di
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cmp al, 0
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je .finish ; If it's null then the string is finished
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cmp al, 5Ah ; 5Ah = 'Z'
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jns .loop ; Ignore if it's more than 'Z'
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cmp al, 41h ; 41h = 'A'
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js .loop ; Ignore if it's less than 'A'
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add al, 20h ; Otherwise subtract 20h to capitalise it
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dec di
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stosb ; Store the new value
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jmp .loop ; Next character
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.finish:
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popa
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ret
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string_lower_case:
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popa
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ret
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string_lower_case: ; to lower case
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pusha
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mov si, ax
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mov di, si
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.loop:
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lodsb ; Load the character into al
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inc di
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cmp al, 0
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je .finish ; If it's null then the string is finished
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cmp al, 5Ah ; 5Ah = 'Z'
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jns .loop ; Ignore if it's more than 'Z'
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cmp al, 41h ; 41h = 'A'
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js .loop ; Ignore if it's less than 'A'
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add al, 20h ; Otherwise subtract 20h to capitalise it
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dec di
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stosb ; Store the new value
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jmp .loop ; Next character
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.finish:
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popa
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ret
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string_input:
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ret
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string_print_2hex:
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