+++ /dev/null
-; To save space, functions that are just called once are
-; implemented as macros instead. Four bytes are saved by
-; avoiding the call / ret instructions.
-
-
-; FINDFILE: Searches for the file in the root directory.
-;
-; Returns:
-;
-; If file not found: CF set
-;
-; If file found: CF clear
-; AX = first cluster of file
-
-
-%macro FINDFILE 0
- ; First, read the whole root directory
- ; into the temporary buffer.
-
- mov ax, word root_dir_start
- mov dx, word root_dir_start_hi
- mov di, nRootDir
- xor bx, bx
- mov es, tempbuf
- call readDisk
- jc ffDone
-
- xor di, di
-
-next_entry: mov cx, 11
- mov si, filename+7c00h
- push di
- repe cmpsb
- pop di
- mov ax, [es:di+1ah] ; get cluster number from directory entry
- clc
- je ffDone
-
- add di, 20h ; go to next directory entry
- cmp byte [es:di], 0 ; if the first byte of the name is 0,
- jnz next_entry ; there is no more files in the directory
-
- stc
-ffDone:
-%endmacro
-
-; GETDRIVEPARMS: Calculate start of some disk areas.
-
-%macro GETDRIVEPARMS 0
- mov si, word nHidden
- mov di, word nHidden_hi
- add si, word resSectors
- adc di, 0 ; DI:SI = first FAT sector
-
- mov word fat_start, si
- mov word fat_start_hi, di
-
- mov al, nFats
- xor ah, ah
- mul word sectPerFat ; DX:AX = total number of FAT sectors
-
- add si, ax
- adc di, dx ; DI:SI = first root directory sector
- mov word root_dir_start, si
- mov word root_dir_start_hi, di
-
- ; Calculate how many sectors the root directory occupies.
- mov bx, bytesPerSector
- mov cl, 5 ; divide BX by 32
- shr bx, cl ; BX = directory entries per sector
-
- mov ax, nRootDir
- xor dx, dx
- div bx
-
- mov nRootDir, ax ; AX = sectors per root directory
-
- add si, ax
- adc di, 0 ; DI:SI = first data sector
-
- mov data_start, si
- mov data_start_hi, di
-%endmacro
-
-; GETFATCHAIN:
-;
-; Reads the FAT chain and stores it in a temporary buffer in the first
-; 64 kb. The FAT chain is stored an array of 16-bit cluster numbers,
-; ending with 0.
-;
-; The file must fit in conventional memory, so it can't be larger than
-; 640 kb. The sector size must be at least 512 bytes, so the FAT chain
-; can't be larger than around 3 kb.
-;
-; Call with: AX = first cluster in chain
-;
-; Returns: CF clear on success, set on error
-
-%macro GETFATCHAIN 0
- push ax ; store first cluster number
-
- ; Load the complete FAT into memory. The FAT can't be larger
- ; than 128 kb, so it should fit in the temporary buffer.
-
- mov es, tempbuf
- xor bx, bx
- mov di, sectPerFat
- mov ax, word fat_start
- mov dx, word fat_start_hi
- call readDisk
- pop ax ; restore first cluster number
- jc boot_error
-
- ; Set ES:DI to the temporary storage for the FAT chain.
- push ds
- push es
- pop ds
- pop es
- mov di, FATBUF
-
-next_clust: stosw ; store cluster number
- mov si, ax ; SI = cluster number
- cmp byte extBoot, 29h
- jne fat_12
- cmp byte [bp+filesys+4], '6' ; check for FAT-16 system
- je fat_16
-
- ; This is a FAT-12 disk.
-
-fat_12: add si, si ; multiply cluster number by 3...
- add si, ax
- shr si, 1 ; ...and divide by 2
- lodsw
-
- ; If the cluster number was even, the cluster value is now in
- ; bits 0-11 of AX. If the cluster number was odd, the cluster
- ; value is in bits 4-15, and must be shifted right 4 bits. If
- ; the number was odd, CF was set in the last shift instruction.
-
- jnc fat_even
- mov cl, 4
- shr ax, cl ; shift the cluster number
-
-fat_even: and ah, 0fh ; mask off the highest 4 bits
- cmp ax, 0fffh ; check for EOF
- jmp short next_test
-
- ; This is a FAT-16 disk. The maximal size of a 16-bit FAT
- ; is 128 kb, so it may not fit within a single 64 kb segment.
-
-fat_16: mov dx, tempbuf
- add si, si ; multiply cluster number by two
- jnc first_half ; if overflow...
- add dh, 10h ; ...add 64 kb to segment value
-
-first_half: mov ds, dx ; DS:SI = pointer to next cluster
- lodsw ; AX = next cluster
-
- cmp ax, 0fff8h ; >= FFF8 = 16-bit EOF
-next_test: jb next_clust ; continue if not EOF
-
-finished: ; Mark end of FAT chain with 0, so we have a single
- ; EOF marker for both FAT-12 and FAT-16 systems.
-
- xor ax, ax
- stosw
-fatError:
-%endmacro
-
-
-; loadFile: Loads the file into memory, one cluster at a time.
-
-%macro LOADFILE 0
- mov es, tempbuf ; set ES:BX to load address
- xor bx, bx
-
- mov si, FATBUF ; set DS:SI to the FAT chain
- push cs
- pop ds
-
-next_cluster: lodsw ; AX = next cluster to read
- or ax, ax ; if EOF...
- je boot_success ; ...boot was successful
-
- dec ax ; cluster numbers start with 2
- dec ax
-
- mov di, word sectPerCluster
- and di, 0ffh ; DI = sectors per cluster
- mul di
- add ax, data_start
- adc dx, data_start_hi ; DX:AX = first sector to read
- call readDisk
- jnc next_cluster
-
-%endmacro
git://git.jankratochvil.net / reactos.git / blobdiff