Objective-C版Base64

#define xx 65

static char exchargeTable[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static unsigned char base64DecodeLookup[256] = {

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, 62,xx,
xx, xx,
63,

52, 53,54,
55, 56,
57, 58,59,
60, 61,
xx, xx,xx,
xx, xx,
xx,

xx, 0, 1,
2, 3,
4, 5, 6,
7, 8,
9, 10,11,
12, 13,
14,

15, 16,17,
18, 19,
20, 21,22,
23, 24,
25, xx,xx,
xx, xx,
xx,

xx, 26,27,
28, 29,
30, 31,32,
33, 34,
35, 36,37,
38, 39,
40,

41, 42,43,
44, 45,
46, 47,48,
49, 50,
51, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx, xx,xx,
xx, xx,
xx,

};

#import "ViewController.h"

@interfaceViewController ()

@end

@implementation NSString (Base64)

- (NSString*)base64Encode{

NSString *ret = nil;

NSMutableString
*codeString = [NSMutableStringstring];

int lenMod = [selflength]%3;

for (int i =0; i <(int)([selflength]/3) ; i++) {

int index = i *3;

[codeString appendFormat:@"%c",exchargeTable[[selfcharacterAtIndex:index]>>2]];

[codeString appendFormat:@"%c",exchargeTable[(([selfcharacterAtIndex:index]&0x03)<<4)|(([selfcharacterAtIndex:index+1]&0xF0)>>4)]];

[codeString appendFormat:@"%c",exchargeTable[(([selfcharacterAtIndex:index+1]&0x0F)<<2)|([selfcharacterAtIndex:index+2]>>6)]];

[codeString appendFormat:@"%c",exchargeTable[[selfcharacterAtIndex:index+2]&0x3F]];

}

if (lenMod != 0) {

int startIndex = ((int)[selflength])/3 *3;

[codeString appendFormat:@"%c",exchargeTable[[selfcharacterAtIndex:startIndex]>>2]];

if (lenMod > 1) {

[codeString appendFormat:@"%c",exchargeTable[(([selfcharacterAtIndex:startIndex]&0x03)<<4)|(([selfcharacterAtIndex:startIndex+1]&0xF0)>>4)]];

[codeString appendFormat:@"%c",exchargeTable[([selfcharacterAtIndex:startIndex+1]&0x0F)<<2]];

}else{

[codeString appendFormat:@"%c",exchargeTable[([selfcharacterAtIndex:startIndex]&0x03)<<4]];

[codeString appendFormat:@"%c",'='];

}

[codeString appendFormat:@"%c",'='];

}

ret = [NSStringstringWithString:codeString];

return ret;

}

- (NSString*)base64Decode{

NSString *ret = nil;

NSMutableString
*decodeString = [NSMutableStringstring];

int lenMod = [selflength]%4;

if (lenMod == 0) {

for (int i =0; i < (int)([selflength]/4); i++) {

int index = i*4;

int char1Pos = base64DecodeLookup[[selfcharacterAtIndex:index]];

int char2Pos = base64DecodeLookup[[selfcharacterAtIndex:index+1]];

int char3Pos = base64DecodeLookup[[selfcharacterAtIndex:index+2]];

int char4Pos = base64DecodeLookup[[selfcharacterAtIndex:index+3]];

[decodeString appendFormat:@"%c",((char1Pos<<2)&0xFC)|((char2Pos&0x30)>>4)];

if ([selfcharacterAtIndex:index+2] !='=') {

[decodeString appendFormat:@"%c",((char2Pos&0x0F)<<4)|((char3Pos>>2)&0x0F)];

if ([selfcharacterAtIndex:index+3] =='=') {

[decodeString appendFormat:@"%c",(char3Pos&0x03)<<6];

}else{

[decodeString appendFormat:@"%c",((char3Pos&0x03)<<6)|(char4Pos&0x3F)];

}

}else{

[decodeString appendFormat:@"%c",(char2Pos&0x0F)<<4];

}

}

}

ret = [NSStringstringWithString:decodeString];

return ret;

}

@end