Input: unsigned char vet[] = { 0xBC,0xFF,0x01 };unsigned short int len = 18;
Output: short int minLung;short int maxLung;
Given a sequence of bits, determine the minimum and maximum length of subsequences consisting of bits 0.
Input:
An array of bytes (BYTE), which should be considered as a sequence of bits.
A WORD value representing the total number of bits in the sequence.
Output:
Minimum length of zero-bit subsequence.
Maximum length of zero-bit subsequence. (If no such subsequence exists, return -1)
The input value defines the exact length of the sequence in bits. This means that the last byte in the array may be partially used. Bits in each byte must be analyzed from the least significant bit to the most significant bit (from right to left, if you look at the byte).
XOR ESI, ESI ; current bit index
XOR EDI, EDI ; zero subsequence length counter
MOV BX, [len] ; load total bit length into BX
MOV [minLung], BX ; initialize minLung with maximum possible length
MOV ECX, -1 ; load -1 into ECX to initialize maxLung
MOV [maxLung], CX ; initialize maxLung with -1
loop_start:
CMP SI, [len] ; compare bit index with length
JGE end_loop ; if index >= length, jump to end_loop
MOV EAX, ESI ; load current bit index into EAX
MOV EDX, EAX ; copy current bit index into EDX
AND EDX, 7 ; bit position within the byte (0...7)
SHR EAX, 3 ; byte number containing the bit
MOV AL, [vet + EAX] ; load current byte
MOV CL, DL ; CL holds current bit position (0-7)
SHR AL, CL ; shift the byte right by bit position
AND AL, 1 ; isolate the current bit
CMP AL, 0 ; check if bit == 0
JNE update_stats ; if bit == 1, jump to update_stats
INC EDI ; increment zero subsequence length
INC ESI ; move to next bit
JMP loop_start ; continue loop
update_stats:
CMP EDI, 0 ; check if zero subsequence length is zero
JE after_update ; if yes, jump to after_update
MOV AX, [minLung] ; load current minimum length into AX
CMP EDI, EAX ; compare current length with minLung
JGE skip_min_update ; if current length >= minLung, skip update
MOV [minLung], DI ; update minLung with current length
skip_min_update:
MOV AX, [maxLung] ; load current maximum length into AX
CMP EDI, EAX ; compare current length with maxLung
JLE skip_max_update ; if current length <= maxLung, skip update
MOV [maxLung], DI ; update maxLung with current length
skip_max_update:
XOR EDI, EDI ; reset zero subsequence counter
after_update:
INC ESI ; move to next bit
JMP loop_start ; continue loop
end_loop:
CMP EDI, 0 ; check if zero subsequence length is zero
JE check_result ; if yes, jump to check_result
MOV AX, [minLung] ; load minLung into AX
CMP DI, AX ; compare current zero subsequence length with minLung
JGE skip_end_min ; if current length >= minLung, skip update
MOV [minLung], DI ; update minLung
skip_end_min:
MOV AX, [maxLung] ; load maxLung into AX
CMP DI, AX ; compare current zero subsequence length with maxLung
JLE skip_end_max ; if current length <= maxLung, skip update
MOV [maxLung], DI ; update maxLung
skip_end_max:
check_result:
MOV AX, [maxLung] ; load maxLung into AX
CMP AX, -1 ; compare maxLung with -1
JNE done ; if not equal, jump to done
MOV AX, -1 ; if equal, set minLung to -1
done:
I can't find the problem. Please help me
The problem is in the way you initialize maxLung
MOV ECX, -1 ; load -1 into ECX to initialize maxLung MOV [maxLung], CX ; initialize maxLung with -1
and how you later use it
MOV AX, [maxLung] ; load current maximum length into AX CMP EDI, EAX ; compare current length with maxLung JLE skip_max_update ; if current length <= maxLung, skip update MOV [maxLung], DI ; update maxLung with current length
The problem is in that CMP EDI, EAX. Had you written this as CMP DI, AX all would have been well.
Because the word maxLung got initialized at -1 or FFFFh, the value in EAX here is actually 0000FFFFh, and so the relatively very small EDI is always going to be less, which in turns means that maxLung never gets its update!
You should make a similar change for updating minLung.