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split pTreeList into struct-of-arrays: eliminates multiply in hot loop #113

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Merged
dloebl merged 1 commit into from
Mar 31, 2026
Merged

split pTreeList into struct-of-arrays: eliminates multiply in hot loop #113

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40 changes: 22 additions & 18 deletions src/cgif_raw.c
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,9 @@ typedef struct {

typedef struct {
uint16_t* pTreeInit; // LZW dictionary tree for the initial dictionary (0-255 max)
uint16_t* pTreeList; // LZW dictionary tree as list (max. number of children per node = 1)
uint16_t* pTreeListMap; // LZW tree list: mapPos per node
uint8_t* pTreeListColor; // LZW tree list: child color per node
uint16_t* pTreeListIdx; // LZW tree list: child LZW index per node
uint16_t* pTreeMap; // LZW dictionary tree as map (backup to pTreeList in case more than 1 child is present)
uint16_t* pLZWData; // pointer to LZW data
const uint8_t* pImageData; // pointer to image data
Expand Down Expand Up @@ -92,27 +94,27 @@ static void resetDict(LZWGenState* pContext, const uint16_t initDictLen) {
++(pContext->LZWPos); // increment position in LZW data
// reset LZW list
memset(pContext->pTreeInit, 0, initDictLen * sizeof(uint16_t) * initDictLen);
memset(pContext->pTreeList, 0, ((sizeof(uint16_t) * 2) + sizeof(uint16_t)) * MAX_DICT_LEN);
memset(pContext->pTreeListMap, 0, sizeof(uint16_t) * MAX_DICT_LEN);
memset(pContext->pTreeListColor, 0, sizeof(uint8_t) * MAX_DICT_LEN);
memset(pContext->pTreeListIdx, 0, sizeof(uint16_t) * MAX_DICT_LEN);
}

/* add new child node */
static void add_child(LZWGenState* pContext, const uint16_t parentIndex, const uint16_t LZWIndex, const uint16_t initDictLen, const uint8_t nextColor) {
uint16_t* pTreeList;
uint16_t mapPos;
uint16_t mapPos;

pTreeList = pContext->pTreeList;
mapPos = pTreeList[parentIndex * (2 + 1)];
mapPos = pContext->pTreeListMap[parentIndex];
if(!mapPos) { // if pTreeMap is not used yet for the parent node
if(pTreeList[parentIndex * (2 + 1) + 2]) { // if at least one child node exists, switch to pTreeMap
if(pContext->pTreeListIdx[parentIndex]) { // if at least one child node exists, switch to pTreeMap
mapPos = pContext->mapPos;
// add child to mapping table (pTreeMap)
memset(pContext->pTreeMap + ((mapPos - 1) * initDictLen), 0, initDictLen * sizeof(uint16_t));
pContext->pTreeMap[(mapPos - 1) * initDictLen + nextColor] = LZWIndex;
pTreeList[parentIndex * (2 + 1)] = mapPos;
pContext->pTreeListMap[parentIndex] = mapPos;
++(pContext->mapPos);
} else { // use the free spot in pTreeList for the child node
pTreeList[parentIndex * (2 + 1) + 1] = nextColor; // color that leads to child node
pTreeList[parentIndex * (2 + 1) + 2] = LZWIndex; // position of child node
pContext->pTreeListColor[parentIndex] = nextColor; // color that leads to child node
pContext->pTreeListIdx[parentIndex] = LZWIndex; // position of child node
}
} else { // directly add child node to pTreeMap
pContext->pTreeMap[(mapPos - 1) * initDictLen + nextColor] = LZWIndex;
Expand All @@ -123,7 +125,6 @@ static void add_child(LZWGenState* pContext, const uint16_t parentIndex, const u
/* find next LZW code representing the longest pixel sequence that is still in the dictionary*/
static int lzw_crawl_tree(LZWGenState* pContext, uint32_t* pStrPos, uint16_t parentIndex, const uint16_t initDictLen) {
uint16_t* pTreeInit;
uint16_t* pTreeList;
uint32_t strPos;
uint16_t nextParent;
uint16_t mapPos;
Expand All @@ -132,7 +133,6 @@ static int lzw_crawl_tree(LZWGenState* pContext, uint32_t* pStrPos, uint16_t par
return CGIF_EINDEX; // error: index in image data out-of-bounds
}
pTreeInit = pContext->pTreeInit;
pTreeList = pContext->pTreeList;
strPos = *pStrPos;
// get the next LZW code from pTreeInit:
// the initial nodes (0-255 max) have more children on average.
Expand Down Expand Up @@ -165,13 +165,13 @@ static int lzw_crawl_tree(LZWGenState* pContext, uint32_t* pStrPos, uint16_t par
return CGIF_EINDEX; // error: index in image data out-of-bounds
}
// first try to find child in LZW list
if(pTreeList[parentIndex * (2 + 1) + 2] && pTreeList[parentIndex * (2 + 1) + 1] == pContext->pImageData[strPos + 1]) {
parentIndex = pTreeList[parentIndex * (2 + 1) + 2];
if(pContext->pTreeListIdx[parentIndex] && pContext->pTreeListColor[parentIndex] == pContext->pImageData[strPos + 1]) {
parentIndex = pContext->pTreeListIdx[parentIndex];
++strPos;
continue;
}
// not found child yet? try to look into the LZW mapping table
mapPos = pContext->pTreeList[parentIndex * (2 + 1)];
mapPos = pContext->pTreeListMap[parentIndex];
if(mapPos) {
nextParent = pContext->pTreeMap[(mapPos - 1) * initDictLen + pContext->pImageData[strPos + 1]];
if(nextParent) {
Expand Down Expand Up @@ -314,8 +314,10 @@ static int LZW_GenerateStream(LZWResult* pResult, const uint32_t numPixel, const
r = CGIF_EALLOC;
goto LZWGENERATE_Cleanup;
}
pContext->pTreeList = malloc(((sizeof(uint16_t) * 2) + sizeof(uint16_t)) * MAX_DICT_LEN);
if(pContext->pTreeList == NULL) {
pContext->pTreeListMap = malloc(sizeof(uint16_t) * MAX_DICT_LEN);
pContext->pTreeListColor = malloc(sizeof(uint8_t) * MAX_DICT_LEN);
pContext->pTreeListIdx = malloc(sizeof(uint16_t) * MAX_DICT_LEN);
if(pContext->pTreeListMap == NULL || pContext->pTreeListColor == NULL || pContext->pTreeListIdx == NULL) {
r = CGIF_EALLOC;
goto LZWGENERATE_Cleanup;
}
Expand Down Expand Up @@ -365,7 +367,9 @@ static int LZW_GenerateStream(LZWResult* pResult, const uint32_t numPixel, const
LZWGENERATE_Cleanup:
free(pContext->pLZWData);
free(pContext->pTreeInit);
free(pContext->pTreeList);
free(pContext->pTreeListMap);
free(pContext->pTreeListColor);
free(pContext->pTreeListIdx);
free(pContext->pTreeMap);
free(pContext);
return r;
Expand Down
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