Question

我无法理解为什么我们将当前群集划分并将结果添加到自身这是代码

mov     ax, WORD [cluster]  ; current cluster

mov     cx, ax              ; copy current cluster 

mov     dx, ax              ; copy current cluster

 shr     dx, 0x0001          ; divide by two 

add     cx, dx              ; sum for (3/2) 

mov     bx, 0x0200          ; location of FAT in memory 

add     bx, cx              ; index into FAT 

mov  dx, WORD [bx]       ; read two bytes from FAT 

test    ax, 0x0001 

jnz     .ODD_CLUSTER ; Remember that each entry in the FAT is a 12 but value. If it represents ; a cluster (0x002 through 0xFEF) then we only want to get those 12 bits ; that represent the next cluster    

  .EVEN_CLUSTER:          
 and     dx, 0000111111111111b      ; take low twelve bits       
   jmp     .DONE 

  .ODD_CLUSTER:        
   shr     dx, 0x0004                 ; take high twelve bits     

.DONE:          
    mov     WORD [cluster], dx         ; store new cluster       
    cmp     dx, 0x0FF0                 ; test for end of file

Answer 1

群集指针各为12位。一个字节是8位，因此FAT表中簇指针的字节偏移量为Items == cluster * 12/8。
要将整数乘以1.5，您可以执行cluster * 1.5，这是此代码的作用。

无法理解如何索引FAT表以在FAT12文件系统中查找新群集

1 个答案: