WIP on FCB disk i/o
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@ -1,31 +0,0 @@
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; IN DL drive number
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; BP ptr to bpb_size'd buffer
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bpb_load:
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push ax
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push dx
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mov [bp+(bpb_size-1)], dl
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; load first sector
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xor dx, dx
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xor ax, ax
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call drive_read
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push cx
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push si
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push di
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; copy BPB to BP
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mov si, (diskbuf+0x0B)
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mov di, bp
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mov cx, (bpb_size-1)
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rep movsb
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pop di
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pop si
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pop cx
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pop dx
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pop ax
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ret
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@ -1,6 +1,32 @@
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; Load a sector from drive.
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; IN DX:AX sector number (lba)
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; BX ptr to FCB
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; OUT CL Sector number
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; CH Cylinder number
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; DH Head number
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drive_chs_calc:
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push bx ; backup fcb ptr
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mov bx, [bx+fcb_spt] ; nos is in BH now
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push bx ; backup nos
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xor bh, bh ; zero out nos so spt is left
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div word bx ; ax:temp = (lba / spt)
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inc dx ; dx:sector = (lba % spt) + 1
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mov cl, dl ; sector number
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pop bx ; restore nos
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xchg bl, bh ; put nos into bl
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xor bh, bh ; zero out spt
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div word bx ; ax:cylinder = (temp / nos)
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; dx:head = (temp % nos)
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mov ch, al ; cylinder number
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mov dh, dl ; head number
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pop bx ; restore fcb ptr
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ret
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; Load a sector from drive.
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; IN DX:AX sector number
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; BP ptr to BPB
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; BX ptr to FCB
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drive_read:
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push ax
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push cx
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@ -12,19 +38,14 @@ drive_read:
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or cx, ax
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jz .fast
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div word [bp+13] ; ax:temp = (lba / spt)
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inc dx ; dx:sector = (lba % spt) + 1
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mov cl, dl ; sector number
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call drive_chs_calc
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div word [bp+15] ; ax:cylinder = (tmp / heads)
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; dx:head = (tmp % heads)
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mov ch, al ; cylinder number
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mov dh, dl ; head number
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mov si, 5 ; retry count
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.try:
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mov dl, [bp+(bpb_size-1)] ; drive number
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mov bx, diskbuf
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mov dl, [bx+fcb_drv] ; drive number
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dec dl
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mov ax, 0x0201
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mov bx, diskbuf
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int 0x13
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.giveup:
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pop si
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@ -7,7 +7,7 @@ exec:
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mov bx, sp
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call fcb_parse
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call fcb_open
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call fcb_open_rootdir
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add sp, fcb_size
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pop bx
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104
kernel/fcb.asm
104
kernel/fcb.asm
@ -1,70 +1,58 @@
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; Parse ASCIIZ string into FCB
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; IN SI ptr to filename
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; BX ptr to FCB
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fcb_parse:
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push di
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push ax
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mov di, bx
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xor ax, ax
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stosb
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.cleanout:
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push di
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mov cx, 0x0A
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mov al, 0x20
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rep stosb
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pop di
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.base_loop:
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call .read
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cmp al, 0x2E
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je .ext_start
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cmp al, 0x20
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je .ret
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stosb
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jmp .base_loop
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.ext_start:
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mov di, bx
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add di, 9
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.ext_loop:
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call .read
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cmp al, 0x20
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je .ret
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stosb
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jmp .ext_loop
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.read:
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lodsb
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test al, al
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jz .eret
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cmp al, 0x0D
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je .eret
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ret
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.eret:
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dec si
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pop ax
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.ret:
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pop ax
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pop di
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ret
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; User-accessible part of FCB (12 bytes)
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%define fcb_drv 0 ; 1 byte
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%define fcb_fn 1 ; 8 bytes
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%define fcb_ext 9 ; 3 bytes
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fcb_open:
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; Drive & FS data (4 bytes)
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%define fcb_spt 12 ; byte sectors per track
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%define fcb_nos 13 ; byte number of sides/heads
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%define fcb_ss 14 ; byte sector size: 2^ss
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%define fcb_cs 15 ; byte cluster size: 2^(ss+cs)
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; Read/Write pointer (12 bytes):
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; Will be overwritten by new filename for CL=17
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%define fcb_fsize 16 ; dword file size
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%define fcb_fptr 20 ; dword handle position
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%define fcb_clus 24 ; word current cluster fptr points in
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%define fcb_co 26 ; word start sector for theoretical cluster 0
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; Link to directory item (3 bytes)
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%define fcb_ds 28 ; word directory sector
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%define fcb_do 30 ; byte directory offset
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fcb_open_rootdir:
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cmp byte [bx], 0
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jne .drivedone
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mov al, default_drive
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inc al
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mov [bx], al
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.drivedone:
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push bp
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sub sp, bpb_size
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mov bp, sp
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mov dl, [bx]
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dec dl
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call bpb_load
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mov ax, [bp]
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mov cx, [bp+2]
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mov dx, [bp+4]
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mov bx, [bp+6]
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xor ax, ax
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xor dx, dx
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; set directory sector to 0 (=rootdir)
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mov [bx+fcb_ds], ax
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; load first sector
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call drive_read
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; transfer sector size
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mov ax, [diskbuf + 0x0B]
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call log2
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mov byte [bx+fcb_ss], al
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; transfer cluster size
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mov al, [diskbuf + 0x0D]
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call log2
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mov byte [bx+fcb_cs], al
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; transfer sectors per track
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mov al, [diskbuf + 0x18]
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mov byte [bx+fcb_spt], al
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; transfer number of heads/sides
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mov al, [diskbuf + 0x1A]
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mov byte [bx+fcb_nos], al
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add sp, bpb_size
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pop bp
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ret
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@ -13,8 +13,7 @@ cpu 8086
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%define default_drive BYTE [0x5B]
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%define fcb_size 16
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%define bpb_size 18
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%define fcb_size 31
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org self
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jmp init
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@ -70,5 +69,6 @@ putc:
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%include "exec.asm"
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%include "fcb.asm"
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%include "bpb.asm"
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%include "fcbparse.asm"
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%include "drive.asm"
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%include "log2.asm"
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14
lib/log2.asm
Normal file
14
lib/log2.asm
Normal file
@ -0,0 +1,14 @@
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; Calculate dual logarithm (int)
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; IN AX number
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; OUT AX dual logarithm
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log2:
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push cx
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mov cx, 16
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.loop:
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sar ax, 1
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loopnz .loop
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xchg ax, cx
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pop cx
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neg ax
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add ax, 15
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ret
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