77 lines
2.0 KiB
NASM
77 lines
2.0 KiB
NASM
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[bits 16]
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; Prints \r\n using BIOS teletype output
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print16_newline:
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push ax
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mov ah, 0x0e ; bios teletype output
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mov al, 0x0a ; newline char
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int 0x10
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mov al, 0x0d ; carriage return
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int 0x10
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pop ax
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ret
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; Prints a null-terminated string beginning in the addr in bx
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print16_string:
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pusha
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print16_string_char_loop:
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mov al, [bx] ; move current value of bx into lower-half of ax
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cmp al, 0 ; check if char is null
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je g_return ; if so, end of string, so return
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; otherwise, print the character
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mov ah, 0x0e ; bios teletype output
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int 0x10
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; Now, advance mem addr of bx by 1 to point to next char
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add bx, 1
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jmp print16_string_char_loop
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; Calls print16_string then print16_newline
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print16:
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call print16_string
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call print16_newline
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ret
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; Template for printing hex strings
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i_print16_hex_template: db '0x0000', 0
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; Prints the value of dx register as a hex-string
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print16_hex_string:
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pusha
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mov cx, 0 ; init looping variable
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print16_hex_string_loop:
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cmp cx, 4 ; check if looping is == 4
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je print16_hex_string_end ; if so, break the loop
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mov ax, dx ; copy the hex value to a mutable register
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and ax, 0x000f ; mask off all but the last bit
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add al, 0x30 ; convert the number to ASCII 0-9
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cmp al, 0x39 ; check if number is 0-9 or a-f
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jle print16_hex_string_update_template ; if 0-9, no further adding needed
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add al, 39 ; otherwise, a-f so offset to proper ASCII range
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print16_hex_string_update_template:
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mov bx, i_print16_hex_template + 5 ; end of ascii template
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sub bx, cx ; make bx point to currently-updated char
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mov [bx], al ; copy ASCII char we computed above into current position of bx
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shr dx, 4 ; shift dx over 1 byte so we can compute next char
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add cx, 1 ; increment looping var
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jmp print16_hex_string_loop
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print16_hex_string_end:
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mov bx, i_print16_hex_template ; copy the filled-out template addr to bx
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call print16_string ; print it out
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jmp g_return
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; Calls print16_hex_string then print16_newline
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print16_hex:
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call print16_hex_string
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call print16_newline
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ret
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