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Reorder fat32 bootsector to reduce number of calls/rets

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Nero 2020-04-04 16:03:02 +00:00
parent 1e99086fc6
commit 3b438074ef
1 changed files with 16 additions and 24 deletions
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40
boot/fat32.asm
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@ -198,26 +198,15 @@ l02e:
ret ret
; Load root directory
loadr: mov ax, 2 loadr: mov ax, 2
xor dx, dx xor dx, dx
jmp load jmp load
loadf: call search ; Load file identified by fsattr
jne fserr ; Directory data is expected at 0x07C00
mov ax, [si+0x1A] loadf: mov si, (0x7C00-0x20)
mov dx, [si+0x14] sloop: add si, 0x20
; load cluster chain DX:AX to [dest]:0
load: mov bx, 0x07C0
lloop: call readc
call next
cmp word dx, 0x0FFF
jne lloop
ret
; Search for first entry with matching fsattr
search: mov si, (0x7C00-0x20)
loop: add si, 0x20
; check if entry is valid ; check if entry is valid
mov al, [si] mov al, [si]
; unallocated direntry ; unallocated direntry
@ -225,12 +214,21 @@ loop: add si, 0x20
jz fserr jz fserr
; deleted files ; deleted files
cmp al, 0xE2 cmp al, 0xE2
je loop je sloop
; check attr ; check attr
mov al, [si+11] mov al, [si+11]
and al, 0x5C and al, 0x5C
cmp al, ah cmp al, ah
jne loop jne sloop
mov ax, [si+0x1A]
mov dx, [si+0x14]
; Load cluster chain DX:AX to 0x07C00
load: mov bx, 0x07C0
lloop: call readc
call next
cmp word dx, 0x0FFF
jne lloop
ret ret
main: mov bp, bpb main: mov bp, bpb
@ -257,12 +255,6 @@ noebio: lea di, [bp-2]
; search for first system file ; search for first system file
mov ah, 0x04 mov ah, 0x04
call loadf call loadf
; jump
xor ax, ax
xor cx, cx
xor dx, dx
xor bx, bx
xor di, di
; restore drive number ; restore drive number
mov dl, [bp+bpb7_dn] mov dl, [bp+bpb7_dn]