Эмулятор процессора Intel 8086 версия 4.05 (ENG) / asm_files / convert_string_to_packed_bcd.asm

Assembler Source Code a:link {text-decoration: none} a:visited {text-decoration: none} a:hover {text-decoration: none; color:#ff0000}     ; convert_string_to_packed_bcd.asm name "convert" ; this program uses a subroutine written in 8086 assembly language ; that can be used for converting a string of number ; (max of 4 ascii digit) to equivalent packed bcd digits. ; bcd is binary coded decimal. ; this program does no screen output. ; to see results click "vars". org 100h jmp start string db '1234' ; 4 ascii digits. packed_bcd dw ? ; two bytes (word) to store 4 digits. start: lea bx, string lea di, packed_bcd call pack_to_bcd_and_binary ret ; return to operating system. ; subroutine written in 8086 assembly language ; that can be used for converting a string of number ; (max of 4 ascii digit) to equivalent packed ; bcd digits. ; input parameters: ; bx - address of source string (4 ascii digits). ; output: ; di - must be set to address for packed bcd (2 bytes). pack_to_bcd_and_binary proc near pusha ; point to 2 upper digits of packed bcd: ; (assumed that we have 4 digits) add di, 1 ; loop only for 2 because every time we ; read 2 digits (2 x 2 = 4 digits) mov cx, 2 ; reset packed bcd: mov word ptr [di], 0 ; to convert a char (0..9) to digit we need ; to subtract 48 (30h) from its ascii code, ; or just clear the upper nibble of a byte. ; mask: 00001111b (0fh) next_digit: mov ax, [bx] ; read 2 digits. and ah, 00001111b and al, 00001111b ; 8086 and all other Intel's microprocessors store less ; significant byte at lower address. xchg al, ah ; move first digit to upper nibble: shl ah, 4 ; pack bcd: or ah, al ; store 2 digits: mov [di], ah ; next packed bcd: sub di, 1 ; next word (2 digits): add bx, 2 loop next_digit popa ret pack_to_bcd_and_binary endp

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