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/**
@file compress.c
@brief An adaptive order-2 PPM range coder
*/
#define ENET_BUILDING_LIB 1
#include <string.h>
#include "enet/enet.h"
typedef struct _ENetSymbol
{
/* binary indexed tree of symbols */
enet_uint8 value;
enet_uint8 count;
enet_uint16 under;
enet_uint16 left, right;
/* context defined by this symbol */
enet_uint16 symbols;
enet_uint16 escapes;
enet_uint16 total;
enet_uint16 parent;
} ENetSymbol;
/* adaptation constants tuned aggressively for small packet sizes rather than large file compression */
enum
{
ENET_RANGE_CODER_TOP = 1<<24,
ENET_RANGE_CODER_BOTTOM = 1<<16,
ENET_CONTEXT_SYMBOL_DELTA = 3,
ENET_CONTEXT_SYMBOL_MINIMUM = 1,
ENET_CONTEXT_ESCAPE_MINIMUM = 1,
ENET_SUBCONTEXT_ORDER = 2,
ENET_SUBCONTEXT_SYMBOL_DELTA = 2,
ENET_SUBCONTEXT_ESCAPE_DELTA = 5
};
/* context exclusion roughly halves compression speed, so disable for now */
#undef ENET_CONTEXT_EXCLUSION
typedef struct _ENetRangeCoder
{
/* only allocate enough symbols for reasonable MTUs, would need to be larger for large file compression */
ENetSymbol symbols[4096];
} ENetRangeCoder;
void *
enet_range_coder_create (void)
{
ENetRangeCoder * rangeCoder = (ENetRangeCoder *) enet_malloc (sizeof (ENetRangeCoder));
if (rangeCoder == NULL)
return NULL;
return rangeCoder;
}
void
enet_range_coder_destroy (void * context)
{
ENetRangeCoder * rangeCoder = (ENetRangeCoder *) context;
if (rangeCoder == NULL)
return;
enet_free (rangeCoder);
}
#define ENET_SYMBOL_CREATE(symbol, value_, count_) \
{ \
symbol = & rangeCoder -> symbols [nextSymbol ++]; \
symbol -> value = value_; \
symbol -> count = count_; \
symbol -> under = count_; \
symbol -> left = 0; \
symbol -> right = 0; \
symbol -> symbols = 0; \
symbol -> escapes = 0; \
symbol -> total = 0; \
symbol -> parent = 0; \
}
#define ENET_CONTEXT_CREATE(context, escapes_, minimum) \
{ \
ENET_SYMBOL_CREATE (context, 0, 0); \
(context) -> escapes = escapes_; \
(context) -> total = escapes_ + 256*minimum; \
(context) -> symbols = 0; \
}
static enet_uint16
enet_symbol_rescale (ENetSymbol * symbol)
{
enet_uint16 total = 0;
for (;;)
{
symbol -> count -= symbol->count >> 1;
symbol -> under = symbol -> count;
if (symbol -> left)
symbol -> under += enet_symbol_rescale (symbol + symbol -> left);
total += symbol -> under;
if (! symbol -> right) break;
symbol += symbol -> right;
}
return total;
}
#define ENET_CONTEXT_RESCALE(context, minimum) \
{ \
(context) -> total = (context) -> symbols ? enet_symbol_rescale ((context) + (context) -> symbols) : 0; \
(context) -> escapes -= (context) -> escapes >> 1; \
(context) -> total += (context) -> escapes + 256*minimum; \
}
#define ENET_RANGE_CODER_OUTPUT(value) \
{ \
if (outData >= outEnd) \
return 0; \
* outData ++ = value; \
}
#define ENET_RANGE_CODER_ENCODE(under, count, total) \
{ \
encodeRange /= (total); \
encodeLow += (under) * encodeRange; \
encodeRange *= (count); \
for (;;) \
{ \
if((encodeLow ^ (encodeLow + encodeRange)) >= ENET_RANGE_CODER_TOP) \
{ \
if(encodeRange >= ENET_RANGE_CODER_BOTTOM) break; \
encodeRange = -encodeLow & (ENET_RANGE_CODER_BOTTOM - 1); \
} \
ENET_RANGE_CODER_OUTPUT (encodeLow >> 24); \
encodeRange <<= 8; \
encodeLow <<= 8; \
} \
}
#define ENET_RANGE_CODER_FLUSH \
{ \
while (encodeLow) \
{ \
ENET_RANGE_CODER_OUTPUT (encodeLow >> 24); \
encodeLow <<= 8; \
} \
}
#define ENET_RANGE_CODER_FREE_SYMBOLS \
{ \
if (nextSymbol >= sizeof (rangeCoder -> symbols) / sizeof (ENetSymbol) - ENET_SUBCONTEXT_ORDER ) \
{ \
nextSymbol = 0; \
ENET_CONTEXT_CREATE (root, ENET_CONTEXT_ESCAPE_MINIMUM, ENET_CONTEXT_SYMBOL_MINIMUM); \
predicted = 0; \
order = 0; \
} \
}
#define ENET_CONTEXT_ENCODE(context, symbol_, value_, under_, count_, update, minimum) \
{ \
under_ = value*minimum; \
count_ = minimum; \
if (! (context) -> symbols) \
{ \
ENET_SYMBOL_CREATE (symbol_, value_, update); \
(context) -> symbols = symbol_ - (context); \
} \
else \
{ \
ENetSymbol * node = (context) + (context) -> symbols; \
for (;;) \
{ \
if (value_ < node -> value) \
{ \
node -> under += update; \
if (node -> left) { node += node -> left; continue; } \
ENET_SYMBOL_CREATE (symbol_, value_, update); \
node -> left = symbol_ - node; \
} \
else \
if (value_ > node -> value) \
{ \
under_ += node -> under; \
if (node -> right) { node += node -> right; continue; } \
ENET_SYMBOL_CREATE (symbol_, value_, update); \
node -> right = symbol_ - node; \
} \
else \
{ \
count_ += node -> count; \
under_ += node -> under - node -> count; \
node -> under += update; \
node -> count += update; \
symbol_ = node; \
} \
break; \
} \
} \
}
#ifdef ENET_CONTEXT_EXCLUSION
static const ENetSymbol emptyContext = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
#define ENET_CONTEXT_WALK(context, body) \
{ \
const ENetSymbol * node = (context) + (context) -> symbols; \
const ENetSymbol * stack [256]; \
size_t stackSize = 0; \
while (node -> left) \
{ \
stack [stackSize ++] = node; \
node += node -> left; \
} \
for (;;) \
{ \
body; \
if (node -> right) \
{ \
node += node -> right; \
while (node -> left) \
{ \
stack [stackSize ++] = node; \
node += node -> left; \
} \
} \
else \
if (stackSize <= 0) \
break; \
else \
node = stack [-- stackSize]; \
} \
}
#define ENET_CONTEXT_ENCODE_EXCLUDE(context, value_, under, total, minimum) \
ENET_CONTEXT_WALK(context, { \
if (node -> value != value_) \
{ \
enet_uint16 parentCount = rangeCoder -> symbols [node -> parent].count + minimum; \
if (node -> value < value_) \
under -= parentCount; \
total -= parentCount; \
} \
})
#endif
size_t
enet_range_coder_compress (void * context, const ENetBuffer * inBuffers, size_t inBufferCount, size_t inLimit, enet_uint8 * outData, size_t outLimit)
{
ENetRangeCoder * rangeCoder = (ENetRangeCoder *) context;
enet_uint8 * outStart = outData, * outEnd = & outData [outLimit];
const enet_uint8 * inData, * inEnd;
enet_uint32 encodeLow = 0, encodeRange = ~0;
ENetSymbol * root;
enet_uint16 predicted = 0;
size_t order = 0, nextSymbol = 0;
if (rangeCoder == NULL || inBufferCount <= 0 || inLimit <= 0)
return 0;
inData = (const enet_uint8 *) inBuffers -> data;
inEnd = & inData [inBuffers -> dataLength];
inBuffers ++;
inBufferCount --;
ENET_CONTEXT_CREATE (root, ENET_CONTEXT_ESCAPE_MINIMUM, ENET_CONTEXT_SYMBOL_MINIMUM);
for (;;)
{
ENetSymbol * subcontext, * symbol;
#ifdef ENET_CONTEXT_EXCLUSION
const ENetSymbol * childContext = & emptyContext;
#endif
enet_uint8 value;
enet_uint16 count, under, * parent = & predicted, total;
if (inData >= inEnd)
{
if (inBufferCount <= 0)
break;
inData = (const enet_uint8 *) inBuffers -> data;
inEnd = & inData [inBuffers -> dataLength];
inBuffers ++;
inBufferCount --;
}
value = * inData ++;
for (subcontext = & rangeCoder -> symbols [predicted];
subcontext != root;
#ifdef ENET_CONTEXT_EXCLUSION
childContext = subcontext,
#endif
subcontext = & rangeCoder -> symbols [subcontext -> parent])
{
ENET_CONTEXT_ENCODE (subcontext, symbol, value, under, count, ENET_SUBCONTEXT_SYMBOL_DELTA, 0);
* parent = symbol - rangeCoder -> symbols;
parent = & symbol -> parent;
total = subcontext -> total;
#ifdef ENET_CONTEXT_EXCLUSION
if (childContext -> total > ENET_SUBCONTEXT_SYMBOL_DELTA + ENET_SUBCONTEXT_ESCAPE_DELTA)
ENET_CONTEXT_ENCODE_EXCLUDE (childContext, value, under, total, 0);
#endif
if (count > 0)
{
ENET_RANGE_CODER_ENCODE (subcontext -> escapes + under, count, total);
}
else
{
if (subcontext -> escapes > 0 && subcontext -> escapes < total)
ENET_RANGE_CODER_ENCODE (0, subcontext -> escapes, total);
subcontext -> escapes += ENET_SUBCONTEXT_ESCAPE_DELTA;
subcontext -> total += ENET_SUBCONTEXT_ESCAPE_DELTA;
}
subcontext -> total += ENET_SUBCONTEXT_SYMBOL_DELTA;
if (count > 0xFF - 2*ENET_SUBCONTEXT_SYMBOL_DELTA || subcontext -> total > ENET_RANGE_CODER_BOTTOM - 0x100)
ENET_CONTEXT_RESCALE (subcontext, 0);
if (count > 0) goto nextInput;
}
ENET_CONTEXT_ENCODE (root, symbol, value, under, count, ENET_CONTEXT_SYMBOL_DELTA, ENET_CONTEXT_SYMBOL_MINIMUM);
* parent = symbol - rangeCoder -> symbols;
parent = & symbol -> parent;
total = root -> total;
#ifdef ENET_CONTEXT_EXCLUSION
if (childContext -> total > ENET_SUBCONTEXT_SYMBOL_DELTA + ENET_SUBCONTEXT_ESCAPE_DELTA)
ENET_CONTEXT_ENCODE_EXCLUDE (childContext, value, under, total, ENET_CONTEXT_SYMBOL_MINIMUM);
#endif
ENET_RANGE_CODER_ENCODE (root -> escapes + under, count, total);
root -> total += ENET_CONTEXT_SYMBOL_DELTA;
if (count > 0xFF - 2*ENET_CONTEXT_SYMBOL_DELTA + ENET_CONTEXT_SYMBOL_MINIMUM || root -> total > ENET_RANGE_CODER_BOTTOM - 0x100)
ENET_CONTEXT_RESCALE (root, ENET_CONTEXT_SYMBOL_MINIMUM);
nextInput:
if (order >= ENET_SUBCONTEXT_ORDER)
predicted = rangeCoder -> symbols [predicted].parent;
else
order ++;
ENET_RANGE_CODER_FREE_SYMBOLS;
}
ENET_RANGE_CODER_FLUSH;
return (size_t) (outData - outStart);
}
#define ENET_RANGE_CODER_SEED \
{ \
if (inData < inEnd) decodeCode |= * inData ++ << 24; \
if (inData < inEnd) decodeCode |= * inData ++ << 16; \
if (inData < inEnd) decodeCode |= * inData ++ << 8; \
if (inData < inEnd) decodeCode |= * inData ++; \
}
#define ENET_RANGE_CODER_READ(total) ((decodeCode - decodeLow) / (decodeRange /= (total)))
#define ENET_RANGE_CODER_DECODE(under, count, total) \
{ \
decodeLow += (under) * decodeRange; \
decodeRange *= (count); \
for (;;) \
{ \
if((decodeLow ^ (decodeLow + decodeRange)) >= ENET_RANGE_CODER_TOP) \
{ \
if(decodeRange >= ENET_RANGE_CODER_BOTTOM) break; \
decodeRange = -decodeLow & (ENET_RANGE_CODER_BOTTOM - 1); \
} \
decodeCode <<= 8; \
if (inData < inEnd) \
decodeCode |= * inData ++; \
decodeRange <<= 8; \
decodeLow <<= 8; \
} \
}
#define ENET_CONTEXT_DECODE(context, symbol_, code, value_, under_, count_, update, minimum, createRoot, visitNode, createRight, createLeft) \
{ \
under_ = 0; \
count_ = minimum; \
if (! (context) -> symbols) \
{ \
createRoot; \
} \
else \
{ \
ENetSymbol * node = (context) + (context) -> symbols; \
for (;;) \
{ \
enet_uint16 after = under_ + node -> under + (node -> value + 1)*minimum, before = node -> count + minimum; \
visitNode; \
if (code >= after) \
{ \
under_ += node -> under; \
if (node -> right) { node += node -> right; continue; } \
createRight; \
} \
else \
if (code < after - before) \
{ \
node -> under += update; \
if (node -> left) { node += node -> left; continue; } \
createLeft; \
} \
else \
{ \
value_ = node -> value; \
count_ += node -> count; \
under_ = after - before; \
node -> under += update; \
node -> count += update; \
symbol_ = node; \
} \
break; \
} \
} \
}
#define ENET_CONTEXT_TRY_DECODE(context, symbol_, code, value_, under_, count_, update, minimum, exclude) \
ENET_CONTEXT_DECODE (context, symbol_, code, value_, under_, count_, update, minimum, return 0, exclude (node -> value, after, before), return 0, return 0)
#define ENET_CONTEXT_ROOT_DECODE(context, symbol_, code, value_, under_, count_, update, minimum, exclude) \
ENET_CONTEXT_DECODE (context, symbol_, code, value_, under_, count_, update, minimum, \
{ \
value_ = code / minimum; \
under_ = code - code%minimum; \
ENET_SYMBOL_CREATE (symbol_, value_, update); \
(context) -> symbols = symbol_ - (context); \
}, \
exclude (node -> value, after, before), \
{ \
value_ = node->value + 1 + (code - after)/minimum; \
under_ = code - (code - after)%minimum; \
ENET_SYMBOL_CREATE (symbol_, value_, update); \
node -> right = symbol_ - node; \
}, \
{ \
value_ = node->value - 1 - (after - before - code - 1)/minimum; \
under_ = code - (after - before - code - 1)%minimum; \
ENET_SYMBOL_CREATE (symbol_, value_, update); \
node -> left = symbol_ - node; \
}) \
#ifdef ENET_CONTEXT_EXCLUSION
typedef struct _ENetExclude
{
enet_uint8 value;
enet_uint16 under;
} ENetExclude;
#define ENET_CONTEXT_DECODE_EXCLUDE(context, total, minimum) \
{ \
enet_uint16 under = 0; \
nextExclude = excludes; \
ENET_CONTEXT_WALK (context, { \
under += rangeCoder -> symbols [node -> parent].count + minimum; \
nextExclude -> value = node -> value; \
nextExclude -> under = under; \
nextExclude ++; \
}); \
total -= under; \
}
#define ENET_CONTEXT_EXCLUDED(value_, after, before) \
{ \
size_t low = 0, high = nextExclude - excludes; \
for(;;) \
{ \
size_t mid = (low + high) >> 1; \
const ENetExclude * exclude = & excludes [mid]; \
if (value_ < exclude -> value) \
{ \
if (low + 1 < high) \
{ \
high = mid; \
continue; \
} \
if (exclude > excludes) \
after -= exclude [-1].under; \
} \
else \
{ \
if (value_ > exclude -> value) \
{ \
if (low + 1 < high) \
{ \
low = mid; \
continue; \
} \
} \
else \
before = 0; \
after -= exclude -> under; \
} \
break; \
} \
}
#endif
#define ENET_CONTEXT_NOT_EXCLUDED(value_, after, before)
size_t
enet_range_coder_decompress (void * context, const enet_uint8 * inData, size_t inLimit, enet_uint8 * outData, size_t outLimit)
{
ENetRangeCoder * rangeCoder = (ENetRangeCoder *) context;
enet_uint8 * outStart = outData, * outEnd = & outData [outLimit];
const enet_uint8 * inEnd = & inData [inLimit];
enet_uint32 decodeLow = 0, decodeCode = 0, decodeRange = ~0;
ENetSymbol * root;
enet_uint16 predicted = 0;
size_t order = 0, nextSymbol = 0;
#ifdef ENET_CONTEXT_EXCLUSION
ENetExclude excludes [256];
ENetExclude * nextExclude = excludes;
#endif
if (rangeCoder == NULL || inLimit <= 0)
return 0;
ENET_CONTEXT_CREATE (root, ENET_CONTEXT_ESCAPE_MINIMUM, ENET_CONTEXT_SYMBOL_MINIMUM);
ENET_RANGE_CODER_SEED;
for (;;)
{
ENetSymbol * subcontext, * symbol, * patch;
#ifdef ENET_CONTEXT_EXCLUSION
const ENetSymbol * childContext = & emptyContext;
#endif
enet_uint8 value = 0;
enet_uint16 code, under, count, bottom, * parent = & predicted, total;
for (subcontext = & rangeCoder -> symbols [predicted];
subcontext != root;
#ifdef ENET_CONTEXT_EXCLUSION
childContext = subcontext,
#endif
subcontext = & rangeCoder -> symbols [subcontext -> parent])
{
if (subcontext -> escapes <= 0)
continue;
total = subcontext -> total;
#ifdef ENET_CONTEXT_EXCLUSION
if (childContext -> total > 0)
ENET_CONTEXT_DECODE_EXCLUDE (childContext, total, 0);
#endif
if (subcontext -> escapes >= total)
continue;
code = ENET_RANGE_CODER_READ (total);
if (code < subcontext -> escapes)
{
ENET_RANGE_CODER_DECODE (0, subcontext -> escapes, total);
continue;
}
code -= subcontext -> escapes;
#ifdef ENET_CONTEXT_EXCLUSION
if (childContext -> total > 0)
{
ENET_CONTEXT_TRY_DECODE (subcontext, symbol, code, value, under, count, ENET_SUBCONTEXT_SYMBOL_DELTA, 0, ENET_CONTEXT_EXCLUDED);
}
else
#endif
{
ENET_CONTEXT_TRY_DECODE (subcontext, symbol, code, value, under, count, ENET_SUBCONTEXT_SYMBOL_DELTA, 0, ENET_CONTEXT_NOT_EXCLUDED);
}
bottom = symbol - rangeCoder -> symbols;
ENET_RANGE_CODER_DECODE (subcontext -> escapes + under, count, total);
subcontext -> total += ENET_SUBCONTEXT_SYMBOL_DELTA;
if (count > 0xFF - 2*ENET_SUBCONTEXT_SYMBOL_DELTA || subcontext -> total > ENET_RANGE_CODER_BOTTOM - 0x100)
ENET_CONTEXT_RESCALE (subcontext, 0);
goto patchContexts;
}
total = root -> total;
#ifdef ENET_CONTEXT_EXCLUSION
if (childContext -> total > 0)
ENET_CONTEXT_DECODE_EXCLUDE (childContext, total, ENET_CONTEXT_SYMBOL_MINIMUM);
#endif
code = ENET_RANGE_CODER_READ (total);
if (code < root -> escapes)
{
ENET_RANGE_CODER_DECODE (0, root -> escapes, total);
break;
}
code -= root -> escapes;
#ifdef ENET_CONTEXT_EXCLUSION
if (childContext -> total > 0)
{
ENET_CONTEXT_ROOT_DECODE (root, symbol, code, value, under, count, ENET_CONTEXT_SYMBOL_DELTA, ENET_CONTEXT_SYMBOL_MINIMUM, ENET_CONTEXT_EXCLUDED);
}
else
#endif
{
ENET_CONTEXT_ROOT_DECODE (root, symbol, code, value, under, count, ENET_CONTEXT_SYMBOL_DELTA, ENET_CONTEXT_SYMBOL_MINIMUM, ENET_CONTEXT_NOT_EXCLUDED);
}
bottom = symbol - rangeCoder -> symbols;
ENET_RANGE_CODER_DECODE (root -> escapes + under, count, total);
root -> total += ENET_CONTEXT_SYMBOL_DELTA;
if (count > 0xFF - 2*ENET_CONTEXT_SYMBOL_DELTA + ENET_CONTEXT_SYMBOL_MINIMUM || root -> total > ENET_RANGE_CODER_BOTTOM - 0x100)
ENET_CONTEXT_RESCALE (root, ENET_CONTEXT_SYMBOL_MINIMUM);
patchContexts:
for (patch = & rangeCoder -> symbols [predicted];
patch != subcontext;
patch = & rangeCoder -> symbols [patch -> parent])
{
ENET_CONTEXT_ENCODE (patch, symbol, value, under, count, ENET_SUBCONTEXT_SYMBOL_DELTA, 0);
* parent = symbol - rangeCoder -> symbols;
parent = & symbol -> parent;
if (count <= 0)
{
patch -> escapes += ENET_SUBCONTEXT_ESCAPE_DELTA;
patch -> total += ENET_SUBCONTEXT_ESCAPE_DELTA;
}
patch -> total += ENET_SUBCONTEXT_SYMBOL_DELTA;
if (count > 0xFF - 2*ENET_SUBCONTEXT_SYMBOL_DELTA || patch -> total > ENET_RANGE_CODER_BOTTOM - 0x100)
ENET_CONTEXT_RESCALE (patch, 0);
}
* parent = bottom;
ENET_RANGE_CODER_OUTPUT (value);
if (order >= ENET_SUBCONTEXT_ORDER)
predicted = rangeCoder -> symbols [predicted].parent;
else
order ++;
ENET_RANGE_CODER_FREE_SYMBOLS;
}
return (size_t) (outData - outStart);
}
/** @defgroup host ENet host functions
@{
*/
/** Sets the packet compressor the host should use to the default range coder.
@param host host to enable the range coder for
@returns 0 on success, < 0 on failure
*/
int
enet_host_compress_with_range_coder (ENetHost * host)
{
ENetCompressor compressor;
memset (& compressor, 0, sizeof (compressor));
compressor.context = enet_range_coder_create();
if (compressor.context == NULL)
return -1;
compressor.compress = enet_range_coder_compress;
compressor.decompress = enet_range_coder_decompress;
compressor.destroy = enet_range_coder_destroy;
enet_host_compress (host, & compressor);
return 0;
}
/** @} */