Decompressed size functions now handle multiframes and distinguish cases

- Add ZSTD_findDecompressedSize
    - Traverses multiple frames to find total output size
- Add ZSTD_getFrameContentSize
    - Gets the decompressed size of a single frame by reading header
- Deprecate ZSTD_getDecompressedSize

lib/legacy/zstd_v07.c

@@ -3968,6 +3968,38 @@ size_t ZSTDv07_decompress(void* dst, size_t dstCapacity, const void* src, size_t
 #endif
 }
 
+size_t ZSTDv07_frameSrcSize(const void* src, size_t srcSize)
+{
+    const BYTE* ip = (const BYTE*)src;
+    size_t remainingSize = srcSize;
+
+    /* check */
+    if (srcSize < ZSTDv07_frameHeaderSize_min+ZSTDv07_blockHeaderSize) return ERROR(srcSize_wrong);
+
+    /* Frame Header */
+    {   size_t const frameHeaderSize = ZSTDv07_frameHeaderSize(src, ZSTDv07_frameHeaderSize_min);
+        if (ZSTDv07_isError(frameHeaderSize)) return frameHeaderSize;
+        if (MEM_readLE32(src) != ZSTDv07_MAGICNUMBER) return ERROR(prefix_unknown);
+        if (srcSize < frameHeaderSize+ZSTDv07_blockHeaderSize) return ERROR(srcSize_wrong);
+        ip += frameHeaderSize; remainingSize -= frameHeaderSize;
+    }
+
+    /* Loop on each block */
+    while (1) {
+        blockProperties_t blockProperties;
+        size_t const cBlockSize = ZSTDv07_getcBlockSize(ip, remainingSize, &blockProperties);
+        if (ZSTDv07_isError(cBlockSize)) return cBlockSize;
+
+        ip += ZSTDv07_blockHeaderSize;
+        remainingSize -= ZSTDv07_blockHeaderSize;
+        if (cBlockSize > remainingSize) return ERROR(srcSize_wrong);
+
+        ip += cBlockSize;
+        remainingSize -= cBlockSize;
+    }
+
+    return ip - (const BYTE*)src;
+}
 
 /*_******************************
 *  Streaming Decompression API