我对这个算法有疑问：
function crc16 = crc16eval(D)
% CRC16EVAL CRC-CCITT check with the polynomial: x^16+x^12+x^5+1
D = uint16(D);
crchi = 255;
crclo = 255;
t = '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';
crc16htab = hex2dec(reshape(t,2,length(t)/2)');
t = '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';
crc16ltab = hex2dec(reshape(t,2,length(t)/2)');
for k = 1:length(D)
ix = double(bitxor(crchi,D(k)))+1;
crchi = bitxor(crclo,crc16htab(ix));
crclo = crc16ltab(ix);
end
crc16 = crchi*256+crclo;
end
我需要将该代码翻译成 Python，并且我已经完成了以下操作：
def crc16eval(D):
crchi = 255
crclo = 255
t = '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'
# crc16htab = hex2dec(reshape(t,2,length(t)/2)');
tarray = [int(n, 16) for n in t] # Recorro el string t, y por cada caracter creo un nuevo entero en el array
crc16htab = reshape(tarray, (2, (len(t)/2) )).transpose()
#print crc16htab
t = '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'
# crc16ltab = hex2dec(reshape(t,2,length(t)/2)');
tarray = [int(n, 16) for n in t] # Recorro el string t, y por cada caracter creo un nuevo entero en el array
crc16ltab = reshape(tarray, (2, (len(t)/2))).transpose()
#print crc16ltab
for k in range(len(D)):
ix = crchi ^ D[k]
crchi = crclo ^ crc16htab[ix]
crclo = crc16ltab[ix]
return crchi*256+crclo
我的问题是下一个：
当我执行 de Python 代码时，计算 de xor 需要很长时间，我认为问题在于
crclo = crc16ltab[ix]
是一个矩阵，计算时间很长。哪个是问题？
该算法的伪代码如下：
The algorithm for the CRC-CCITT is below described. Note that all operations are on bytes.
A = new byte
B = temp byte
CRCHI = High byte (most significant) of the 16-bit CRC
CRCLO = Low byte (least significant) of the 16-bit CRC
START:
FOR A = FIRST_BYTE TO LAST_BYTE IN BLOCK DO:
A = A XOR CRCHI
CRCHI = A
SHIFT A RIGHT FOUR TIMES (ZERO FILL)
A = A XOR CRCHI {IJKLMNOP}
CRCHI = CRCLO { swap CRCHI, CRCLO }
CRCLO = A
ROTATE A LEFT 4 TIMES {MNOPIJKL}
B=A { temp save }
ROTATE A LEFT ONCE {NOPIJKLM}
A = A AND $1F {000IJLLM}
CRCHI = A XOR CRCHI
A = B AND $F0 {MNOP0000}
CRCHI = A XOR CRCHI { CRCHI complete }
ROTATE B LEFT ONCE {NOP0000M}
B = B AND $ E0 {NOP00000}
CRCLO = B XOR CRCLO { CRCLO complete }
DOEND;
FINISH.
我的问题是：为什么我的 python 代码需要很长时间才能执行？怎么了？我认为的问题在于
for k in range(len(D)):
ix = crchi ^ D[k]
crchi = crclo ^ crc16htab[ix]
crclo = crc16ltab[ix]
非常感谢！