/** @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; } /** @} */