added ZSTD_initStaticCCtx()

makes it possible to statically or externally allocate CCtx.
static CCtx will only use provided memory area,
it will never resize nor malloc.

doc/zstd_manual.html

@@ -423,6 +423,22 @@ size_t ZSTD_estimateDDictSize(size_t dictSize);
 </b><p>  Create a ZSTD compression context using external alloc and free functions 
 </p></pre><BR>
 
+<pre><b>ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize);
+</b><p>  workspace: The memory area to emplace the context into.
+             Provided pointer must 8-bytes aligned.
+             It must outlive context usage.
+  workspaceSize: Use ZSTD_estimateCCtxSize() or ZSTD_estimateCStreamSize()
+                 to determine how large workspace must be to support scenario.
+ @return : pointer to ZSTD_CCtx*, or NULL if error (size too small)
+  Note : zstd will never resize nor malloc() when using a static cctx.
+         If it needs more memory than available, it will simply error out.
+  Note 2 : there is no corresponding "free" function.
+           Since workspace was allocated externally, it must be freed externally too.
+  Limitation : currently not compatible with internal CDict creation, such as
+               ZSTD_CCtx_loadDictionary() or ZSTD_initCStream_usingDict().
+ 
+</p></pre><BR>
+
 <pre><b>typedef enum {
     ZSTD_p_forceWindow,   </b>/* Force back-references to remain < windowSize, even when referencing Dictionary content (default:0) */<b>
     ZSTD_p_forceRawDict   </b>/* Force loading dictionary in "content-only" mode (no header analysis) */<b>
@@ -714,7 +730,7 @@ size_t ZSTD_CDict_loadDictionary(ZSTD_CDict* cdict, const void* dict, size_t dic
 
 <h3>Advanced Streaming compression functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
 size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize);   </b>/**< pledgedSrcSize must be correct, a size of 0 means unknown.  for a frame size of 0 use initCStream_advanced */<b>
-size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); </b>/**< note: a dict will not be used if dict == NULL or dictSize < 8. This result in the creation of an internal CDict */<b>
+size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); </b>/**< creates of an internal CDict (incompatible with static CCtx), except if dict == NULL or dictSize < 8, in which case no dict is used. */<b>
 size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
                                              ZSTD_parameters params, unsigned long long pledgedSrcSize);  </b>/**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */<b>
 size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict);  </b>/**< note : cdict will just be referenced, and must outlive compression session */<b>

lib/compress/zstd_compress.c

@@ -126,6 +126,7 @@ struct ZSTD_CCtx_s {
     U64 consumedSrcSize;
     XXH64_state_t xxhState;
     ZSTD_customMem customMem;
+    size_t staticSize;
 
     seqStore_t seqStore;    /* sequences storage ptrs */
     U32* hashTable;
@@ -175,9 +176,38 @@ ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem)
     return cctx;
 }
 
+ZSTD_CCtx* ZSTD_initStaticCCtx(void *workspace, size_t workspaceSize)
+{
+    ZSTD_CCtx* cctx = (ZSTD_CCtx*) workspace;
+    if (workspaceSize <= sizeof(ZSTD_CCtx)) return NULL;  /* minimum size */
+    if ((size_t)workspace & 7) return NULL;  /* must be 8-aligned */
+    memset(workspace, 0, workspaceSize);
+    cctx->staticSize = workspaceSize;
+    cctx->workSpace = (void*)(cctx+1);
+    cctx->workSpaceSize = workspaceSize - sizeof(ZSTD_CCtx);
+
+    /* entropy space (never moves) */
+    /* note : this code should be shared with resetCCtx, instead of copied */
+    {   void* ptr = cctx->workSpace;
+        cctx->hufCTable = (HUF_CElt*)ptr;
+        ptr = (char*)cctx->hufCTable + hufCTable_size;  /* note : HUF_CElt* is incomplete type, size is estimated via macro */
+        cctx->offcodeCTable = (FSE_CTable*) ptr;
+        ptr = (char*)ptr + offcodeCTable_size;
+        cctx->matchlengthCTable = (FSE_CTable*) ptr;
+        ptr = (char*)ptr + matchlengthCTable_size;
+        cctx->litlengthCTable = (FSE_CTable*) ptr;
+        ptr = (char*)ptr + litlengthCTable_size;
+        assert(((size_t)ptr & 3) == 0);   /* ensure correct alignment */
+        cctx->entropyScratchSpace = (unsigned*) ptr;
+    }
+
+    return cctx;
+}
+
 size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx)
 {
     if (cctx==NULL) return 0;   /* support free on NULL */
+    assert(!cctx->staticSize);  /* not compatible with static CCtx */
     ZSTD_free(cctx->workSpace, cctx->customMem);
     cctx->workSpace = NULL;
     ZSTD_freeCDict(cctx->cdictLocal);
@@ -337,6 +367,7 @@ ZSTDLIB_API size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long lo
 ZSTDLIB_API size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize)
 {
     if (cctx->streamStage != zcss_init) return ERROR(stage_wrong);
+    if (cctx->staticSize) return ERROR(memory_allocation);  /* no malloc for static CCtx */
     ZSTD_freeCDict(cctx->cdictLocal);  /* in case one already exists */
     if (dict==NULL || dictSize==0) {   /* no dictionary mode */
         cctx->cdictLocal = NULL;
@@ -448,6 +479,17 @@ size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams)
     return sizeof(ZSTD_CCtx) + neededSpace;
 }
 
+size_t ZSTD_estimateCStreamSize(ZSTD_compressionParameters cParams)
+{
+    size_t const CCtxSize = ZSTD_estimateCCtxSize(cParams);
+    size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, (size_t)1 << cParams.windowLog);
+    size_t const inBuffSize = ((size_t)1 << cParams.windowLog) + blockSize;
+    size_t const outBuffSize = ZSTD_compressBound(blockSize) + 1;
+    size_t const streamingSize = inBuffSize + outBuffSize;
+
+    return CCtxSize + streamingSize;
+}
+
 
 static U32 ZSTD_equivalentParams(ZSTD_compressionParameters cParams1,
                                  ZSTD_compressionParameters cParams2)
@@ -532,9 +574,14 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
                                         buffInSize + buffOutSize : 0;
             size_t const neededSpace = entropySpace + optSpace + tableSpace
                                      + tokenSpace + bufferSpace;
-            if (zc->workSpaceSize < neededSpace) {
+
+            if (zc->workSpaceSize < neededSpace) {  /* too small : resize /*/
                 DEBUGLOG(5, "Need to update workSpaceSize from %uK to %uK \n",
-                            (unsigned)zc->workSpaceSize>>10, (unsigned)neededSpace>>10);
+                            (unsigned)zc->workSpaceSize>>10,
+                            (unsigned)neededSpace>>10);
+                /* static cctx : no resize, error out */
+                if (zc->staticSize) return ERROR(memory_allocation);
+
                 zc->workSpaceSize = 0;
                 ZSTD_free(zc->workSpace, zc->customMem);
                 zc->workSpace = ZSTD_malloc(neededSpace, zc->customMem);
@@ -3362,16 +3409,6 @@ size_t ZSTD_freeCStream(ZSTD_CStream* zcs)
     return ZSTD_freeCCtx(zcs);   /* same object */
 }
 
-size_t ZSTD_estimateCStreamSize(ZSTD_compressionParameters cParams)
-{
-    size_t const CCtxSize = ZSTD_estimateCCtxSize(cParams);
-    size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, (size_t)1 << cParams.windowLog);
-    size_t const inBuffSize = ((size_t)1 << cParams.windowLog) + blockSize;
-    size_t const outBuffSize = ZSTD_compressBound(blockSize) + 1;
-    size_t const streamingSize = inBuffSize + outBuffSize;
-
-    return CCtxSize + streamingSize;
-}
 
 
 /*======   Initialization   ======*/
@@ -3446,6 +3483,10 @@ static size_t ZSTD_initCStream_internal(ZSTD_CStream* zcs,
     zcs->cdict = NULL;
 
     if (dict && dictSize >= 8) {
+        if (zcs->staticSize) {   /* static CCtx : never uses malloc */
+            /* incompatible with internal cdict creation */
+            return ERROR(memory_allocation);
+        }
         ZSTD_freeCDict(zcs->cdictLocal);
         zcs->cdictLocal = ZSTD_createCDict_advanced(dict, dictSize, 0 /* copy */, params.cParams, zcs->customMem);
         if (zcs->cdictLocal == NULL) return ERROR(memory_allocation);

lib/zstd.h

@@ -511,6 +511,22 @@ ZSTDLIB_API size_t ZSTD_estimateDDictSize(size_t dictSize);
  *  Create a ZSTD compression context using external alloc and free functions */
 ZSTDLIB_API ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
 
+/*! ZSTD_initStaticCCtx() : initialize a fixed-size zstd compression context
+ *  workspace: The memory area to emplace the context into.
+ *             Provided pointer must 8-bytes aligned.
+ *             It must outlive context usage.
+ *  workspaceSize: Use ZSTD_estimateCCtxSize() or ZSTD_estimateCStreamSize()
+ *                 to determine how large workspace must be to support scenario.
+ * @return : pointer to ZSTD_CCtx*, or NULL if error (size too small)
+ *  Note : zstd will never resize nor malloc() when using a static cctx.
+ *         If it needs more memory than available, it will simply error out.
+ *  Note 2 : there is no corresponding "free" function.
+ *           Since workspace was allocated externally, it must be freed externally too.
+ *  Limitation : currently not compatible with internal CDict creation, such as
+ *               ZSTD_CCtx_loadDictionary() or ZSTD_initCStream_usingDict().
+ */
+ZSTDLIB_API ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize);
+
 
 /* !!! Soon to be deprecated !!! */
 typedef enum {
@@ -841,7 +857,7 @@ ZSTDLIB_API unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
 /*=====   Advanced Streaming compression functions  =====*/
 ZSTDLIB_API ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
 ZSTDLIB_API size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize);   /**< pledgedSrcSize must be correct, a size of 0 means unknown.  for a frame size of 0 use initCStream_advanced */
-ZSTDLIB_API size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); /**< note: a dict will not be used if dict == NULL or dictSize < 8. This result in the creation of an internal CDict */
+ZSTDLIB_API size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); /**< creates of an internal CDict (incompatible with static CCtx), except if dict == NULL or dictSize < 8, in which case no dict is used. */
 ZSTDLIB_API size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
                                              ZSTD_parameters params, unsigned long long pledgedSrcSize);  /**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */
 ZSTDLIB_API size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict);  /**< note : cdict will just be referenced, and must outlive compression session */

tests/fuzzer.c

@@ -190,6 +190,63 @@ static int basicUnitTests(U32 seed, double compressibility)
     DISPLAYLEVEL(4, "OK \n");
 
 
+    /* Static CCtx tests */
+#define STATIC_CCTX_LEVEL 3
+    DISPLAYLEVEL(4, "test%3i : create static CCtx for level %u :", testNb++, STATIC_CCTX_LEVEL);
+    {   ZSTD_compressionParameters const cParams = ZSTD_getCParams(STATIC_CCTX_LEVEL, 0, 0);
+        size_t const staticCCtxSize = ZSTD_estimateCStreamSize(cParams);
+        void* staticCCtxBuffer = malloc(staticCCtxSize);
+        if (staticCCtxBuffer==NULL) {
+            DISPLAY("Not enough memory, aborting\n");
+            testResult = 1;
+            goto _end;
+        }
+        {   ZSTD_CCtx* staticCCtx = ZSTD_initStaticCCtx(staticCCtxBuffer, staticCCtxSize);
+            if (staticCCtx==NULL) goto _output_error;
+            DISPLAYLEVEL(4, "OK \n");
+
+            DISPLAYLEVEL(4, "test%3i : init CCtx for level %u : ", testNb++, STATIC_CCTX_LEVEL);
+            { size_t const r = ZSTD_compressBegin(staticCCtx, STATIC_CCTX_LEVEL);
+              if (ZSTD_isError(r)) goto _output_error; }
+            DISPLAYLEVEL(4, "OK \n");
+
+            DISPLAYLEVEL(4, "test%3i : simple compression test with static CCtx : ", testNb++);
+            CHECKPLUS(r, ZSTD_compressCCtx(staticCCtx,
+                            compressedBuffer, ZSTD_compressBound(CNBuffSize),
+                            CNBuffer, CNBuffSize, STATIC_CCTX_LEVEL),
+                      cSize=r );
+            DISPLAYLEVEL(4, "OK (%u bytes : %.2f%%)\n", (U32)cSize, (double)cSize/CNBuffSize*100);
+
+            DISPLAYLEVEL(4, "test%3i : decompress verification test : ", testNb++);
+            { size_t const r = ZSTD_decompress(decodedBuffer, CNBuffSize, compressedBuffer, cSize);
+              if (r != CNBuffSize) goto _output_error; }
+            DISPLAYLEVEL(4, "OK \n");
+
+            DISPLAYLEVEL(4, "test%3i : init CCtx for too large level (must fail) : ", testNb++);
+            { size_t const r = ZSTD_compressBegin(staticCCtx, ZSTD_maxCLevel());
+              if (!ZSTD_isError(r)) goto _output_error; }
+            DISPLAYLEVEL(4, "OK \n");
+
+            DISPLAYLEVEL(4, "test%3i : init CCtx for small level %u (should work again) : ", testNb++, 1);
+            { size_t const r = ZSTD_compressBegin(staticCCtx, 1);
+              if (ZSTD_isError(r)) goto _output_error; }
+            DISPLAYLEVEL(4, "OK \n");
+
+            DISPLAYLEVEL(4, "test%3i : init CStream for small level %u : ", testNb++, 1);
+            { size_t const r = ZSTD_initCStream(staticCCtx, 1);
+              if (ZSTD_isError(r)) goto _output_error; }
+            DISPLAYLEVEL(4, "OK \n");
+
+            DISPLAYLEVEL(4, "test%3i : init CStream with dictionary (should fail) : ", testNb++);
+            { size_t const r = ZSTD_initCStream_usingDict(staticCCtx, CNBuffer, 64 KB, 1);
+              if (!ZSTD_isError(r)) goto _output_error; }
+            DISPLAYLEVEL(4, "OK \n");
+        }
+        free(staticCCtxBuffer);
+    }
+
+
+
     /* ZSTDMT simple MT compression test */
     DISPLAYLEVEL(4, "test%3i : create ZSTDMT CCtx : ", testNb++);
     {   ZSTDMT_CCtx* mtctx = ZSTDMT_createCCtx(2);