以十六進制搜索特定字節

Question

我有一個buffer[]包括十六進制字節，我想搜索此緩衝區以查找特定字節。例如：

我的緩衝區有4096字節，我想在這個搜索如果字節45 34 67 23（在一起）在這個緩衝區內（像在緩衝區中搜索字符串）。

你有什麼想法我該怎麼做？編程語言是C

Answer 1

只是「蠻力」吧:)

haystacklen = 4096; 
needlelen = 4; 

foundat = -1; 
index = 0; /* start at a different number if searching for 2nd occurrence */ 
while (index < haystacklen - needlelen + 1) { 
    if ((buffer[index + 0] == 45) 
    && (buffer[index + 1] == 34) 
    && (buffer[index + 2] == 67) 
    && (buffer[index + 3] == 23)) 
    { 
     foundat = index; 
    } 
    index++; 
} 
/* foundat has the index of the 1st search bytes or -1 */ 

Answer 2

你也可以使用這個更快的版本。但是你必須記住，這隻適用於x86/little endian處理器，因爲MAKEDWORD宏。

#define MAKEDWORD(a,b,c,d) ((uint32_t) (((uint32_t)a) & 0xFF) | ((((uint32_t)b) & 0xFF) << 8) | ((((uint32_t)c) & 0xFF) << 16) | ((((uint32_t)d) & 0xFF) << 24)) 
#define NEEDLE (MAKEDWORD(45,34,67,23)) 

// get the start and end address of the buffer 
uint8_t *ptrEndBuffer = ((uint8_t*)buffer) + (4096 - sizeof(NEEDLE)); 
uint8_t *ptrStartBuffer = (uint8_t*)buffer - 1; // subtract -1 because we also want to get index 0 

// while the result is not 0 we are good 
while (ptrEndBuffer - ptrStartBuffer) { 
    if ((*(uint32_t*)ptrEndBuffer) == NEEDLE) // get an whole integer instead of just one char 
     break; // leave the loop if we found a match 

    ptrEndBuffer--; 
} 

// the index will be -1 if we couldn't find a match else we subtract the start address + the 1 we first removed from the end buffer 
int index = ((ptrEndBuffer == ptrStartBuffer) ? (-1) : (ptrEndBuffer - (ptrStartBuffer + 1)));