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compact.c
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C/C++ Source or Header
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1997-07-27
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8KB
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701 lines
/*
* compact.c
*
* message compaction / encryption
*/
#include "ctdl.h"
/*
* history
*
* 89Jun05 HAW Created.
*/
/*
* Contents
*
* StartEncode() Start baudot-v encoding.
* StopEncode() Stop same.
* Encode() Does actual encoding of a byte.
* Combine() Work function for encoding.
* StartDecode() Start Decoding.
* StopDecode() Stop Decoding.
* Decode() Actual decoding function.
* Decode2() Work function.
*/
/* #define DEBUG */
void StopEncode(void);
static int Combine(int val);
static int Decode2(int val);
#define NO_SET 4 /* no such set */
#define CAPS 0
#define SPEC_CHARS 3
#define COMP_SPACE 26 /* universal */
#define ZERO_COMP 16
#define RET_COMP 17
static struct
{
char Set, /* code set */
CompValue; /* position in code set */
}
compress[] =
{
{
0, 0
}
,
{
2, 10
}
,
{
2, 11
}
,
{
2, 12
}
,
{
2, 13
}
, /* ' ' - '$' */
{
2, 14
}
,
{
2, 15
}
,
{
2, 16
}
,
{
2, 17
}
,
{
2, 18
}
, /* '%' - ')' */
{
2, 19
}
,
{
2, 20
}
,
{
2, 21
}
,
{
2, 22
}
,
{
2, 23
}
, /* '*' - '.' */
{
2, 24
}
,
{
2, 0
}
,
{
2, 1
}
,
{
2, 2
}
,
{
2, 3
}
, /* '/' - '3' */
{
2, 4
}
,
{
2, 5
}
,
{
2, 6
}
,
{
2, 7
}
,
{
2, 8
}
, /* '4' - '8' */
{
2, 9
}
,
{
2, 25
}
,
{
3, 0
}
,
{
3, 1
}
,
{
3, 2
}
, /* '9' - '=' */
{
3, 3
}
,
{
3, 4
}
,
{
3, 5
}
,
{
0, 0
}
,
{
0, 1
}
, /* '>' - 'B' */
{
0, 2
}
,
{
0, 3
}
,
{
0, 4
}
,
{
0, 5
}
,
{
0, 6
}
, /* 'C' - 'G' */
{
0, 7
}
,
{
0, 8
}
,
{
0, 9
}
,
{
0, 10
}
,
{
0, 11
}
, /* 'H' - 'L' */
{
0, 12
}
,
{
0, 13
}
,
{
0, 14
}
,
{
0, 15
}
,
{
0, 16
}
, /* 'M' - 'Q' */
{
0, 17
}
,
{
0, 18
}
,
{
0, 19
}
,
{
0, 20
}
,
{
0, 21
}
, /* 'R' - 'V' */
{
0, 22
}
,
{
0, 23
}
,
{
0, 24
}
,
{
0, 25
}
,
{
3, 6
}
, /* 'W' - '[' */
{
3, 7
}
,
{
3, 8
}
,
{
3, 9
}
,
{
3, 10
}
,
{
3, 11
}
, /* '\' - '`' */
{
1, 0
}
,
{
1, 1
}
,
{
1, 2
}
,
{
1, 3
}
,
{
1, 4
}
, /* 'a' - 'e' */
{
1, 5
}
,
{
1, 6
}
,
{
1, 7
}
,
{
1, 8
}
,
{
1, 9
}
, /* 'f' - 'i' */
{
1, 10
}
,
{
1, 11
}
,
{
1, 12
}
,
{
1, 13
}
,
{
1, 14
}
, /* 'j' - 'o' */
{
1, 15
}
,
{
1, 16
}
,
{
1, 17
}
,
{
1, 18
}
,
{
1, 19
}
, /* 'p' - 't' */
{
1, 20
}
,
{
1, 21
}
,
{
1, 22
}
,
{
1, 23
}
,
{
1, 24
}
, /* 'u' - 'y' */
{
1, 25
}
,
{
3, 12
}
,
{
3, 13
}
,
{
3, 14
}
,
{
3, 15
}
/* 'z' - '~' */
};
static char EncCurSet;
static int BitsUsed, SendVal, Next, EncodeByteCount;
int (*EncOF)(int c);
int StartEncode(int (*func)(int c))
{
BitsUsed = 0;
EncCurSet = NO_SET;
EncOF = func;
SendVal = 0;
EncodeByteCount = 0;
return 1;
}
void StopEncode()
{
if (EncodeByteCount == 0) return; /* don't bother */
Combine(31);
Combine(0);
Combine(0);
Combine(0);
}
int Encode(int c)
{
int toReturn = TRUE;
EncodeByteCount++;
switch (c)
{
case ' ': /* space exists in all code sets */
if (EncCurSet == NO_SET)
{
Combine(CAPS + 27);
EncCurSet = CAPS;
}
toReturn = Combine(COMP_SPACE); break;
case 0:
case '\r':
if (EncCurSet != SPEC_CHARS)
{
Combine(SPEC_CHARS + 27);
EncCurSet = SPEC_CHARS;
}
toReturn = Combine((c == 0) ? ZERO_COMP : RET_COMP);
break;
default:
/* discard if not printable, C/R, or 0 byte */
if (c >= ' ' && c < '~')
{
if (compress[c - 32].Set != EncCurSet)
{
Combine(compress[c - 32].Set + 27);
EncCurSet = compress[c - 32].Set;
}
toReturn = Combine(compress[c - 32].CompValue);
}
}
return toReturn;
}
static int Combine(int val)
{
int toReturn;
SendVal |= (val << BitsUsed);
SendVal &= 0xff;
Next = (val >> BitsUsed);
BitsUsed += 5;
if (BitsUsed >= 8)
{
toReturn = (*EncOF)(SendVal);
SendVal = val >> (13 - BitsUsed);
BitsUsed %= 8;
}
else toReturn = TRUE;
return toReturn;
}
void StopDecode(void);
#define NO_CAPS 1
#define NUMERICS 2
#define FINISHED 4 /* finished with encoded data */
#define INIT_SET 5 /* an initial value */
static char Numerics[] =
{
'0', '1', '2', '3', '4',
'5', '6', '7', '8', '9',
'!', '\"', '#', '$', '%',
'&', '\'', '(', ')', '*',
'+', ',', '-', '.', '/',
':'
};
static char SpecChars[] =
{
';', '<' , '=', '>', '?', '@', '[', '\\',
']', 0x5e, '_', '`', '{', '|', '}', '~', 0,'\r'
};
static char DecCurSet;
static int ThisVal, NB;
int (*DecOF)(int val);
int StartDecode(int (*func)())
{
ThisVal = 0;
DecCurSet = INIT_SET;
DecOF = func;
NB = 5;
return 1;
}
void StopDecode()
{
}
int Decode(int c)
{
static int mask[] =
{
0, 1, 3, 7, 0xf, 0x1f
};
int AB;
if (DecCurSet == FINISHED) return TRUE;
if (!Decode2(c & mask[NB])) return FALSE;
c >>= NB;
AB = 8 - NB;
if (AB >= 5)
{
ThisVal = 0;
AB -= 5;
NB = 5;
if (!Decode2(c & mask[NB])) return FALSE;
c >>= 5;
}
NB = 5 - AB;
ThisVal = c;
return TRUE;
}
static int Decode2(int val)
{
int toReturn = FALSE;
char Used;
if (DecCurSet == FINISHED) return TRUE;
ThisVal += (val << (5 - NB));
switch (ThisVal - 27)
{
case CAPS:
case NO_CAPS:
case NUMERICS:
case SPEC_CHARS:
case FINISHED:
DecCurSet = ThisVal - 27;
Used = TRUE;
toReturn = TRUE;
break;
default: Used = FALSE;
}
/* Discard if no set defined. */
if (!Used)
{
if (DecCurSet == INIT_SET)
toReturn = TRUE; /* True for any valid code set */
else if (ThisVal == COMP_SPACE) toReturn = (*DecOF)(' ');
else switch (DecCurSet)
{
case CAPS: toReturn = (*DecOF)('A' + ThisVal); break;
case NO_CAPS: toReturn = (*DecOF)('a' + ThisVal); break;
case NUMERICS: toReturn = (*DecOF)(Numerics[ThisVal]); break;
case SPEC_CHARS: toReturn = (*DecOF)(SpecChars[ThisVal]); break;
}
}
return toReturn;
}
