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/********************************************************************************
* *
* B a s e - 8 5 E n c o d i n g / D e c o d i n g *
* *
*********************************************************************************
* Copyright (C) 2018,2022 by Jeroen van der Zijp. All Rights Reserved. *
*********************************************************************************
* This library is free software; you can redistribute it and/or modify *
* it under the terms of the GNU Lesser General Public License as published by *
* the Free Software Foundation; either version 3 of the License, or *
* (at your option) any later version. *
* *
* This library is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU Lesser General Public License for more details. *
* *
* You should have received a copy of the GNU Lesser General Public License *
* along with this program. If not, see <http://www.gnu.org/licenses/> *
********************************************************************************/
#include "xincs.h"
#include "fxver.h"
#include "fxdefs.h"
/*
Notes:
- Encode/decode binary data to or from ascii85.
- Could do with some error checking; encode can't fail, but decode can,
if input character is not in expected set, what do we do? [suggest we
skip it, maybe].
- Which base85 is most useful? Adobe, rfc1924, Z85,
- 85^5 = 4384852500, which is just larger than 256^4=4294967295; thus, 5
bytes needed to encode each 4 bytes.
- Encode 4 bytes of source into 5 bytes of destination, using only 85 printable
ASCII symbols.
*/
using namespace FX;
/*******************************************************************************/
namespace FX {
// Ascii85 encoding table
static const FXchar encode[86]="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~";
// Ascii85 decoding table
static const FXuchar decode[256]={
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 62, 128, 63, 64, 65, 66, 128, 67, 68, 69, 70, 128, 71, 128, 128,
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 128, 72, 73, 74, 75, 76,
77, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 128, 128, 128, 78, 79,
80, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 81, 82, 83, 84, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
};
// Encode src to dst in base85, each 4 bytes is encoded as 5 ascii bytes
FXchar* fxencode85(FXchar* dst,FXchar* dstend,const FXchar* src,const FXchar* srcend){
FXchar* ptr=dst;
FXuchar c0,c1,c2,c3,c4;
FXuint value;
while(ptr+4<dstend && src+3<srcend){ // Encode whole groups
c0=src[0];
c1=src[1];
c2=src[2];
c3=src[3];
value=(c0<<24)|(c1<<16)|(c2<<8)|c3;
c0=value/52200625; // No modulo needed
c1=(value/614125)%85;
c2=(value/7225)%85;
c3=(value/85)%85;
c4=value%85;
ptr[0]=encode[c0];
ptr[1]=encode[c1];
ptr[2]=encode[c2];
ptr[3]=encode[c3];
ptr[4]=encode[c4];
src+=4;
ptr+=5;
}
if(ptr+4<dstend && src<srcend){ // Encode partial group
c0=src[0];
c1=0;
c2=0;
if(src+1<srcend){
c1=src[1];
if(src+2<srcend){
c2=src[2];
}
}
value=(c0<<24)|(c1<<16)|(c2<<8);
c0=value/52200625; // No modulo needed
c1=(value/614125)%85;
c2=(value/7225)%85;
c3=(value/85)%85;
c4=value%85;
ptr[0]=encode[c0];
ptr[1]=encode[c1];
ptr[2]=encode[c2];
ptr[3]=encode[c3];
ptr[4]=encode[c4];
ptr+=5;
}
if(ptr<dstend){ // Terminate string
ptr[0]='\0';
}
return ptr;
}
// Decode src to dst from base85; assume input is a multiple of 5,
// and output a whole multiple of 4.
FXchar* fxdecode85(FXchar* dst,FXchar* dstend,const FXchar* src,const FXchar* srcend){
const FXchar* end=src;
FXchar* ptr=dst;
FXuchar c0,c1,c2,c3,c4;
FXuint value;
while(end<srcend && decode[(FXuchar)end[0]]!=128){
++end;
}
while(ptr+3<dstend && src+4<end){ // Decode whole group of 4
c0=src[0];
c1=src[1];
c2=src[2];
c3=src[3];
c4=src[4];
c0=decode[c0];
c1=decode[c1];
c2=decode[c2];
c3=decode[c3];
c4=decode[c4];
value=((c0*85+c1)*85+c2)*85+c3;
if(value>=50529027 && (value+c4)>50529027) break; // Overflow check
value=value*85+c4;
c0=value>>24;
c1=value>>16;
c2=value>>8;
c3=value;
ptr[0]=c0;
ptr[1]=c1;
ptr[2]=c2;
ptr[3]=c3;
src+=5;
ptr+=4;
}
if(ptr<dstend){ // Terminate string
ptr[0]='\0';
}
return ptr;
}
}
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