引言
然而,在对100MB文件进行MD5、Adler32和CRC32测试时,我发现了一个重要的发现,那就是它们居然花费同样的时间。这只能意味着两件事情之一,我猜测,在Android设备上,文件系统是瓶颈,无法快速地将数据提供给算法,或者在实现JNI时我犯了基本错误,后者我可以接受。
像图像、MP3和小于10MB的文件这样的小文件使用MD5算法只需几秒钟即可完成哈希值计算。
我的问题是我有100-700MB大小的文件。
我的要求是下载的文件需要与原始源文件匹配。
我做了一些测试,为大小为100MB的文件制作MD5哈希。
在HTC Desire Android v2.2设备上,我运行了JNI本地测试和Java MessageDigest.getInstance("MD5");
测试。
两个测试都计算了相同文件的MD5值,并且两个测试的运行时间大约为1-2分钟。我关闭了调试功能。
据我理解,本地测试应该更快。
我如何将哈希计算时间降低到比如在上述设备上的10-15秒。
这样做的代价当然是碰撞准确性,但我可以接受哈希值在百万分之一以内不同。
更新
我不是C语言专家,但这里是我的MD5测试C代码。它的速度并不比Java MessageDigest
快多少。感觉就像在Android主UI线程上运行。
#include <android/log.h>
#include <stdio.h>
#include <sys/types.h>
#include <time.h>
#include <string.h>
#include <inttypes.h>
#include <jni.h>
#include <stdlib.h>
/* typedef a 32 bit type */
typedef unsigned long int UINT4;
/* Data structure for MD5 (Message Digest) computation */
typedef struct {
UINT4 i[2]; /* number of _bits_ handled mod 2^64 */
UINT4 buf[4]; /* scratch buffer */
unsigned char in[64]; /* input buffer */
unsigned char digest[16]; /* actual digest after MD5Final call */
} MD5_CTX;
void MD5Init ();
void MD5Update ();
void MD5Final ();
/* forward declaration */
static void Transform ();
static unsigned char PADDING[64] = {
0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};
/* F, G and H are basic MD5 functions: selection, majority, parity */
#define F(x, y, z) (((x) & (y)) | ((~x) & (z)))
#define G(x, y, z) (((x) & (z)) | ((y) & (~z)))
#define H(x, y, z) ((x) ^ (y) ^ (z))
#define I(x, y, z) ((y) ^ ((x) | (~z)))
/* ROTATE_LEFT rotates x left n bits */
#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4 */
/* Rotation is separate from addition to prevent recomputation */
#define FF(a, b, c, d, x, s, ac) \
{(a) += F ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
#define GG(a, b, c, d, x, s, ac) \
{(a) += G ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
#define HH(a, b, c, d, x, s, ac) \
{(a) += H ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
#define II(a, b, c, d, x, s, ac) \
{(a) += I ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
void MD5Init (mdContext)
MD5_CTX *mdContext;
{
mdContext->i[0] = mdContext->i[1] = (UINT4)0;
/* Load magic initialization constants.
*/
mdContext->buf[0] = (UINT4)0x67452301;
mdContext->buf[1] = (UINT4)0xefcdab89;
mdContext->buf[2] = (UINT4)0x98badcfe;
mdContext->buf[3] = (UINT4)0x10325476;
}
void MD5Update (mdContext, inBuf, inLen)
MD5_CTX *mdContext;
unsigned char *inBuf;
unsigned int inLen;
{
UINT4 in[16];
int mdi;
unsigned int i, ii;
/* compute number of bytes mod 64 */
mdi = (int)((mdContext->i[0] >> 3) & 0x3F);
/* update number of bits */
if ((mdContext->i[0] + ((UINT4)inLen << 3)) < mdContext->i[0])
mdContext->i[1]++;
mdContext->i[0] += ((UINT4)inLen << 3);
mdContext->i[1] += ((UINT4)inLen >> 29);
while (inLen--) {
/* add new character to buffer, increment mdi */
mdContext->in[mdi++] = *inBuf++;
/* transform if necessary */
if (mdi == 0x40) {
for (i = 0, ii = 0; i < 16; i++, ii += 4)
in[i] = (((UINT4)mdContext->in[ii+3]) << 24) |
(((UINT4)mdContext->in[ii+2]) << 16) |
(((UINT4)mdContext->in[ii+1]) << 8) |
((UINT4)mdContext->in[ii]);
Transform (mdContext->buf, in);
mdi = 0;
}
}
}
void MD5Final (mdContext)
MD5_CTX *mdContext;
{
UINT4 in[16];
int mdi;
unsigned int i, ii;
unsigned int padLen;
/* save number of bits */
in[14] = mdContext->i[0];
in[15] = mdContext->i[1];
/* compute number of bytes mod 64 */
mdi = (int)((mdContext->i[0] >> 3) & 0x3F);
/* pad out to 56 mod 64 */
padLen = (mdi < 56) ? (56 - mdi) : (120 - mdi);
MD5Update (mdContext, PADDING, padLen);
/* append length in bits and transform */
for (i = 0, ii = 0; i < 14; i++, ii += 4)
in[i] = (((UINT4)mdContext->in[ii+3]) << 24) |
(((UINT4)mdContext->in[ii+2]) << 16) |
(((UINT4)mdContext->in[ii+1]) << 8) |
((UINT4)mdContext->in[ii]);
Transform (mdContext->buf, in);
/* store buffer in digest */
for (i = 0, ii = 0; i < 4; i++, ii += 4) {
mdContext->digest[ii] = (unsigned char)(mdContext->buf[i] & 0xFF);
mdContext->digest[ii+1] =
(unsigned char)((mdContext->buf[i] >> 8) & 0xFF);
mdContext->digest[ii+2] =
(unsigned char)((mdContext->buf[i] >> 16) & 0xFF);
mdContext->digest[ii+3] =
(unsigned char)((mdContext->buf[i] >> 24) & 0xFF);
}
}
/* Basic MD5 step. Transform buf based on in.
*/
static void Transform (buf, in)
UINT4 *buf;
UINT4 *in;
{
UINT4 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
/* Round 1 */
#define S11 7
#define S12 12
#define S13 17
#define S14 22
FF ( a, b, c, d, in[ 0], S11, 3614090360u); /* 1 */
FF ( d, a, b, c, in[ 1], S12, 3905402710u); /* 2 */
FF ( c, d, a, b, in[ 2], S13, 606105819u); /* 3 */
FF ( b, c, d, a, in[ 3], S14, 3250441966u); /* 4 */
FF ( a, b, c, d, in[ 4], S11, 4118548399u); /* 5 */
FF ( d, a, b, c, in[ 5], S12, 1200080426u); /* 6 */
FF ( c, d, a, b, in[ 6], S13, 2821735955u); /* 7 */
FF ( b, c, d, a, in[ 7], S14, 4249261313u); /* 8 */
FF ( a, b, c, d, in[ 8], S11, 1770035416u); /* 9 */
FF ( d, a, b, c, in[ 9], S12, 2336552879u); /* 10 */
FF ( c, d, a, b, in[10], S13, 4294925233u); /* 11 */
FF ( b, c, d, a, in[11], S14, 2304563134u); /* 12 */
FF ( a, b, c, d, in[12], S11, 1804603682u); /* 13 */
FF ( d, a, b, c, in[13], S12, 4254626195u); /* 14 */
FF ( c, d, a, b, in[14], S13, 2792965006u); /* 15 */
FF ( b, c, d, a, in[15], S14, 1236535329u); /* 16 */
/* Round 2 */
#define S21 5
#define S22 9
#define S23 14
#define S24 20
GG ( a, b, c, d, in[ 1], S21, 4129170786u); /* 17 */
GG ( d, a, b, c, in[ 6], S22, 3225465664u); /* 18 */
GG ( c, d, a, b, in[11], S23, 643717713u); /* 19 */
GG ( b, c, d, a, in[ 0], S24, 3921069994u); /* 20 */
GG ( a, b, c, d, in[ 5], S21, 3593408605u); /* 21 */
GG ( d, a, b, c, in[10], S22, 38016083u); /* 22 */
GG ( c, d, a, b, in[15], S23, 3634488961u); /* 23 */
GG ( b, c, d, a, in[ 4], S24, 3889429448u); /* 24 */
GG ( a, b, c, d, in[ 9], S21, 568446438u); /* 25 */
GG ( d, a, b, c, in[14], S22, 3275163606u); /* 26 */
GG ( c, d, a, b, in[ 3], S23, 4107603335u); /* 27 */
GG ( b, c, d, a, in[ 8], S24, 1163531501u); /* 28 */
GG ( a, b, c, d, in[13], S21, 2850285829u); /* 29 */
GG ( d, a, b, c, in[ 2], S22, 4243563512u); /* 30 */
GG ( c, d, a, b, in[ 7], S23, 1735328473u); /* 31 */
GG ( b, c, d, a, in[12], S24, 2368359562u); /* 32 */
/* Round 3 */
#define S31 4
#define S32 11
#define S33 16
#define S34 23
HH ( a, b, c, d, in[ 5], S31, 4294588738u); /* 33 */
HH ( d, a, b, c, in[ 8], S32, 2272392833u); /* 34 */
HH ( c, d, a, b, in[11], S33, 1839030562u); /* 35 */
HH ( b, c, d, a, in[14], S34, 4259657740u); /* 36 */
HH ( a, b, c, d, in[ 1], S31, 2763975236u); /* 37 */
HH ( d, a, b, c, in[ 4], S32, 1272893353u); /* 38 */
HH ( c, d, a, b, in[ 7], S33, 4139469664u); /* 39 */
HH ( b, c, d, a, in[10], S34, 3200236656u); /* 40 */
HH ( a, b, c, d, in[13], S31, 681279174u); /* 41 */
HH ( d, a, b, c, in[ 0], S32, 3936430074u); /* 42 */
HH ( c, d, a, b, in[ 3], S33, 3572445317u); /* 43 */
HH ( b, c, d, a, in[ 6], S34, 76029189u); /* 44 */
HH ( a, b, c, d, in[ 9], S31, 3654602809u); /* 45 */
HH ( d, a, b, c, in[12], S32, 3873151461u); /* 46 */
HH ( c, d, a, b, in[15], S33, 530742520u); /* 47 */
HH ( b, c, d, a, in[ 2], S34, 3299628645u); /* 48 */
/* Round 4 */
#define S41 6
#define S42 10
#define S43 15
#define S44 21
II ( a, b, c, d, in[ 0], S41, 4096336452u); /* 49 */
II ( d, a, b, c, in[ 7], S42, 1126891415u); /* 50 */
II ( c, d, a, b, in[14], S43, 2878612391u); /* 51 */
II ( b, c, d, a, in[ 5], S44, 4237533241u); /* 52 */
II ( a, b, c, d, in[12], S41, 1700485571u); /* 53 */
II ( d, a, b, c, in[ 3], S42, 2399980690u); /* 54 */
II ( c, d, a, b, in[10], S43, 4293915773u); /* 55 */
II ( b, c, d, a, in[ 1], S44, 2240044497u); /* 56 */
II ( a, b, c, d, in[ 8], S41, 1873313359u); /* 57 */
II ( d, a, b, c, in[15], S42, 4264355552u); /* 58 */
II ( c, d, a, b, in[ 6], S43, 2734768916u); /* 59 */
II ( b, c, d, a, in[13], S44, 1309151649u); /* 60 */
II ( a, b, c, d, in[ 4], S41, 4149444226u); /* 61 */
II ( d, a, b, c, in[11], S42, 3174756917u); /* 62 */
II ( c, d, a, b, in[ 2], S43, 718787259u); /* 63 */
II ( b, c, d, a, in[ 9], S44, 3951481745u); /* 64 */
buf[0] += a;
buf[1] += b;
buf[2] += c;
buf[3] += d;
}
JNIEXPORT jstring
Java_com_carlsberg_IntentServiceSendFiles_gethash( JNIEnv* env, jobject thiz ,
jstring filename)
{
const char *fi = (*env)->GetStringUTFChars(env,filename, 0);
FILE *inFile = fopen (fi, "rb");
MD5_CTX mdContext;
int bytes;
unsigned char data[1024];
if (inFile == NULL) {
printf ("%s can't be opened.\n",fi);
return;
}
MD5Init (&mdContext);
while ((bytes = fread (data, 1, 1024, inFile)) != 0)
MD5Update (&mdContext, data, bytes);
MD5Final (&mdContext);
fclose (inFile);
char tempValue[33]; // 32 hex digits + 0-terminator
int i;
// convert to hex
for (i = 0; i < 16; ++i)
sprintf(tempValue + 2*i, "%02x", (unsigned char)mdContext.digest[i]);
return (*env)->NewStringUTF(env,tempValue );
}