java 转C的问题
有没有对JAVA熟悉的，帮忙转下代码
current = (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3));
这个怎么表示？用C语言
完成代码如下：
import java.text.StringCharacterIterator;
import java.text.CharacterIterator;
/**
* See the BASE64MailboxEncoder for a description of the RFC2060 and how
* mailbox names should be encoded. This class will do the correct decoding
* for mailbox names.
*
* @authorChristopher Cotton
*/
public class BASE64MailboxDecoder {
public static String decode(String original) {
if (original == null || original.length() == 0)
return original;
boolean changedString = false;
int copyTo = 0;
// it will always be less than the original
char[] chars = new char[original.length()];
StringCharacterIterator iter = new StringCharacterIterator(original);
for(char c = iter.first(); c != CharacterIterator.DONE;
c = iter.next()) {
if (c == '&') {
changedString = true;
copyTo = base64decode(chars, copyTo, iter);
} else {
chars[copyTo++] = c;
}
}
// now create our string from the char array
if (changedString) {
return new String(chars, 0, copyTo);
} else {
return original;
}
}
protected static int base64decode(char[] buffer, int offset,
CharacterIterator iter) {
boolean firsttime = true;
int leftover = -1;
while(true) {
// get the first byte
byte orig_0 = (byte) iter.next();
if (orig_0 == -1) break; // no more chars
if (orig_0 == '-') {
if (firsttime) {
// means we got the string "&-" which is turned into a "&"
buffer[offset++] = '&';
}
// we are done now
break;
}
firsttime = false;
// next byte
byte orig_1 = (byte) iter.next();
if (orig_1 == -1 || orig_1 == '-')
break; // no more chars, invalid base64
byte a, b, current;
a = pem_convert_array[orig_0 & 0xff];
b = pem_convert_array[orig_1 & 0xff];
// The first decoded byte
current = (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3));
// use the leftover to create a Unicode Character (2 bytes)
if (leftover != -1) {
buffer[offset++] = (char)(leftover << 8 | (current & 0xff));
leftover = -1;
} else {
leftover = current & 0xff;
}
byte orig_2 = (byte) iter.next();
if (orig_2 == '=') { // End of this BASE64 encoding
continue;
} else if (orig_2 == -1 || orig_2 == '-') {
break; // no more chars
}
// second decoded byte
a = b;
b = pem_convert_array[orig_2 & 0xff];
current = (byte)(((a << 4) & 0xf0) | ((b >>> 2) & 0xf));
// use the leftover to create a Unicode Character (2 bytes)
if (leftover != -1) {
buffer[offset++] = (char)(leftover << 8 | (current & 0xff));
leftover = -1;
} else {
leftover = current & 0xff;
}
byte orig_3 = (byte) iter.next();
if (orig_3 == '=') { // End of this BASE64 encoding
continue;
} else if (orig_3 == -1 || orig_3 == '-') {
break; // no more chars
}
// The third decoded byte
a = b;
b = pem_convert_array[orig_3 & 0xff];
current = (byte)(((a << 6) & 0xc0) | (b & 0x3f));
// use the leftover to create a Unicode Character (2 bytes)
if (leftover != -1) {
buffer[offset++] = (char)(leftover << 8 | (current & 0xff));
leftover = -1;
} else {
leftover = current & 0xff;
}
}
return offset;
}
/**
* This character array provides the character to value map
* based on RFC1521, but with the modification from RFC2060
* which changes the '/' to a ','.
*/
// shared with BASE64MailboxEncoder
static final char pem_array[] = {
'A','B','C','D','E','F','G','H', // 0
'I','J','K','L','M','N','O','P', // 1
'Q','R','S','T','U','V','W','X', // 2
'Y','Z','a','b','c','d','e','f', // 3
'g','h','i','j','k','l','m','n', // 4
'o','p','q','r','s','t','u','v', // 5
'w','x','y','z','0','1','2','3', // 6
'4','5','6','7','8','9','+',',' // 7
};
private static final byte pem_convert_array[] = new byte[256];
static {
for (int i = 0; i < 255; i++)
pem_convert_array[i] = -1;
for(int i = 0; i < pem_array.length; i++)
pem_convert_array[pem_array[i]] = (byte) i;
}
}
[解决办法]
BYTE current = (BYTE)(((a << 2) & 0xfc)
[解决办法]
((b >>> 4) & 3));
[解决办法]
单纯那句, 看不出是什么语言.
thinking in java 的预科,
直接 java 上手的程序员还是欠一些.
[解决办法]
current = (byte)(((a << 2) & 0xfc)
[解决办法]
((b >> 4) & 3));
这个怎么表示？用C语言
这个用c语言标识，也是这样的，没什么区别
[解决办法]
直接转成C语言代码比较长。
[解决办法]
C语言没有>>>
C语言只保证unsigned是逻辑右移，对于signed要看编译器实现了。
[解决办法]
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define BASE64_VALUE_SZ 256
int base64_value[BASE64_VALUE_SZ];
const unsigned char alphabet[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
class Base64Utility {
public:
Base64Utility();
int base64_encode(char *src, int srclen, char *dst, int tail);
int base64_decode(char *src, int srclen, char *dst);
private:
void base_64_init(void);
};
Base64Utility::Base64Utility() {
base_64_init();
}
void Base64Utility::base_64_init(void) {
int i;
for (i = 0; i < BASE64_VALUE_SZ; i++) base64_value[i] = -1;
for (i = 0; i < 64; i++) base64_value[(int) alphabet[i]] = i;
base64_value['='] = 0;
}
int Base64Utility::base64_encode(char *src, int srclen, char *dst, int tail) {
int bits, char_count, len;
char *o_char, *lim, *o_lim;
unsigned char c;
if ( !src
[解决办法]
!dst) return 0;
len = srclen;
lim = src + len;
o_char = dst;
o_lim = dst + (len*4)/3 + 1;
char_count = 0;
bits = 0;
while ( (src < lim) && (o_char < o_lim)) {
c = *(src++);
bits += c;
char_count++;
if (char_count == 3) {
*(o_char++) = alphabet[bits >> 18];
*(o_char++) = alphabet[(bits >> 12) & 0x3f];
*(o_char++) = alphabet[(bits >> 6) & 0x3f];
*(o_char++) = alphabet[bits & 0x3f];
bits = 0;
char_count = 0;
} else {
bits <<= 8;
}
}
if (char_count != 0) {
bits <<= 16 - (8 * char_count);
*(o_char++) = alphabet[bits >> 18];
*(o_char++) = alphabet[(bits >> 12) & 0x3f];
if (char_count == 1) {
if (tail) {
*(o_char++) = '=';
*(o_char++) = '=';
}
} else {
*(o_char++) = alphabet[(bits >> 6) & 0x3f];
if (tail) {
*(o_char++) = '=';
}
}
}
*(o_char) = 0;
return strlen(dst);
}
int Base64Utility::base64_decode(char *src, int srclen, char *dst) {
int j;
unsigned int k;
int c, base_result_sz;
long val;
if (!src
[解决办法]
!dst) return 0;
base_result_sz = srclen;
val = c = 0;
for (j = 0; *src; src++) {
k = (int) *src % BASE64_VALUE_SZ;
if (base64_value[k] < 0) continue;
val <<= 6;
val += base64_value[k];
if (++c < 4) continue;
dst[j++] = (char) (val >> 16);
dst[j++] = (val >> 8) & 0xff;
dst[j++] = val & 0xff;
val = c = 0;
}
switch (c) {
case 2://xxxxxx xx0000
dst[j++] = (val >> 4) & 0xff;
break;
case 3://XXXXXX XXxxxx xxxx00
dst[j++] = (char) (val >> 10);
dst[j++] = (val >> 2) & 0xff;
break;
}
return j;
}
Base64Utility b64u;
#define MAXLENS 1024768
#define MAXLEND 1366360
char bufd[MAXLEND];
char bufs[MAXLENS];
FILE *fs,*fd;
int fsize;
int main(int argc,char *argv[]) {
if (argc<4) {
USE:
printf("%s <-e
[解决办法]
-E
[解决办法]
-d> srcfile desfile\n",argv[0]);
return 1;
}
if (stricmp(argv[1],"-e") && stricmp(argv[1],"-d")) goto USE;
if (0==stricmp(argv[1],"-e")) {
fs=fopen(argv[2],"rb");
if (NULL==fs) {
printf("Can not open file %s!\n",argv[2]);
return 2;
}
fsize=fread(bufs,1,MAXLENS,fs);
if (fsize<=0) {
fclose(fs);
printf("Can not read file %s!\n",argv[2]);
return 3;
}
if (MAXLENS==fsize) printf("Warning: Up to %d bytes.\n",MAXLENS);
fclose(fs);
b64u.base64_encode(bufs,fsize,bufd,('E'==argv[2][1]));
fd=fopen(argv[3],"w");
if (NULL==fd) {
printf("Can not create file %s!\n",argv[3]);
return 4;
}
fprintf(fd,"%s",bufd);
fclose(fd);
} else {//0==stricmp(argv[1],"-d")
fd=fopen(argv[2],"rb");
if (NULL==fd) {
printf("Can not open file %s!\n",argv[2]);
return 2;
}
fsize=fread(bufd,1,MAXLEND,fd);
if (fsize<=0) {
fclose(fd);
printf("Can not read file %s!\n",argv[2]);
return 3;
}
if (MAXLEND==fsize) printf("Warning: Up to %d bytes.\n",MAXLEND);
fclose(fd);
fsize=b64u.base64_decode(bufd,fsize,bufs);
fs=fopen(argv[3],"wb");
if (NULL==fs) {
printf("Can not create file %s!\n",argv[3]);
return 4;
}
if (fsize!=(int)fwrite(bufs,1,fsize,fs)) {
printf("Write %s error!\n",argv[3]);
fclose(fs);
return 5;
}
fclose(fs);
}
return 0;
}
[解决办法]
