Add dictionary random access example

1 files changed, 280 insertions, 0 deletions

diff --git a/examples/dictionaryRandomAccess.c b/examples/dictionaryRandomAccess.c
new file mode 100644
index 0000000..6acf99b
--- /dev/null
+++ b/examples/dictionaryRandomAccess.c
@@ -0,0 +1,280 @@
+// LZ4 API example : Dictionary Random Access
+
+#ifdef _MSC_VER    /* Visual Studio */
+#  define _CRT_SECURE_NO_WARNINGS
+#  define snprintf sprintf_s
+#endif
+#include "lz4.h"
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MIN(x, y) (x) < (y) ? (x) : (y)
+
+enum {
+    BLOCK_BYTES = 1024,  /* 1 KiB of uncompressed data in a block */
+    DICTIONARY_BYTES = 1024, /* Load a 1 KiB dictionary */
+    MAX_BLOCKS = 1024 /* For simplicity of implementation */
+};
+
+/**
+ * Magic bytes for this test case.
+ * This is not a great magic number because it is a common word in ASCII.
+ * However, it is important to have some versioning system in your format.
+ */
+const char kTestMagic[] = { 'T', 'E', 'S', 'T' };
+
+
+void write_int(FILE* fp, int i) {
+    size_t written = fwrite(&i, sizeof(i), 1, fp);
+    if (written != 1) { exit(10); }
+}
+
+void write_bin(FILE* fp, const void* array, size_t arrayBytes) {
+    size_t written = fwrite(array, 1, arrayBytes, fp);
+    if (written != arrayBytes) { exit(11); }
+}
+
+void read_int(FILE* fp, int* i) {
+    size_t read = fread(i, sizeof(*i), 1, fp);
+    if (read != 1) { exit(12); }
+}
+
+size_t read_bin(FILE* fp, void* array, size_t arrayBytes) {
+    size_t read = fread(array, 1, arrayBytes, fp);
+    if (ferror(fp)) { exit(12); }
+    return read;
+}
+
+void seek_bin(FILE* fp, long offset, int origin) {
+    if (fseek(fp, offset, origin)) { exit(14); }
+}
+
+
+void test_compress(FILE* outFp, FILE* inpFp, void *dict, int dictSize)
+{
+    LZ4_stream_t lz4Stream_body;
+    LZ4_stream_t* lz4Stream = &lz4Stream_body;
+
+    char inpBuf[BLOCK_BYTES];
+    int offsets[MAX_BLOCKS];
+    int *offsetsEnd = offsets;
+
+
+    LZ4_resetStream(lz4Stream);
+
+    /* Write header magic */
+    write_bin(outFp, kTestMagic, sizeof(kTestMagic));
+
+    *offsetsEnd++ = sizeof(kTestMagic);
+    /* Write compressed data blocks.  Each block contains BLOCK_BYTES of plain
+       data except possibly the last. */
+    for(;;) {
+        const int inpBytes = (int) read_bin(inpFp, inpBuf, BLOCK_BYTES);
+        if(0 == inpBytes) {
+            break;
+        }
+
+        /* Forget previously compressed data and load the dictionary */
+        LZ4_loadDict(lz4Stream, dict, dictSize);
+        {
+            char cmpBuf[LZ4_COMPRESSBOUND(BLOCK_BYTES)];
+            const int cmpBytes = LZ4_compress_fast_continue(
+                lz4Stream, inpBuf, cmpBuf, inpBytes, sizeof(cmpBuf), 1);
+            if(cmpBytes <= 0) { exit(1); }
+            write_bin(outFp, cmpBuf, (size_t)cmpBytes);
+            /* Keep track of the offsets */
+            *offsetsEnd = *(offsetsEnd - 1) + cmpBytes;
+            ++offsetsEnd;
+        }
+        if (offsetsEnd - offsets > MAX_BLOCKS) { exit(2); }
+    }
+    /* Write the tailing jump table */
+    {
+        int *ptr = offsets;
+        while (ptr != offsetsEnd) {
+            write_int(outFp, *ptr++);
+        }
+        write_int(outFp, offsetsEnd - offsets);
+    }
+}
+
+
+void test_decompress(FILE* outFp, FILE* inpFp, void *dict, int dictSize, int offset, int length)
+{
+    LZ4_streamDecode_t lz4StreamDecode_body;
+    LZ4_streamDecode_t* lz4StreamDecode = &lz4StreamDecode_body;
+
+    /* The blocks [currentBlock, endBlock) contain the data we want */
+    int currentBlock = offset / BLOCK_BYTES;
+    int endBlock = ((offset + length - 1) / BLOCK_BYTES) + 1;
+
+    char decBuf[BLOCK_BYTES];
+    int offsets[MAX_BLOCKS];
+
+    /* Special cases */
+    if (length == 0) { return; }
+
+    /* Read the magic bytes */
+    {
+        char magic[sizeof(kTestMagic)];
+        size_t read = read_bin(inpFp, magic, sizeof(magic));
+        if (read != sizeof(magic)) { exit(1); }
+        if (memcmp(kTestMagic, magic, sizeof(magic))) { exit(2); }
+    }
+
+    /* Read the offsets tail */
+    {
+        int numOffsets;
+        int block;
+        int *offsetsPtr = offsets;
+        seek_bin(inpFp, -4, SEEK_END);
+        read_int(inpFp, &numOffsets);
+        if (numOffsets <= endBlock) { exit(3); }
+        seek_bin(inpFp, -4 * (numOffsets + 1), SEEK_END);
+        for (block = 0; block <= endBlock; ++block) {
+            read_int(inpFp, offsetsPtr++);
+        }
+    }
+    /* Seek to the first block to read */
+    seek_bin(inpFp, offsets[currentBlock], SEEK_SET);
+    offset = offset % BLOCK_BYTES;
+
+    /* Start decoding */
+    for(; currentBlock < endBlock; ++currentBlock) {
+        char cmpBuf[LZ4_COMPRESSBOUND(BLOCK_BYTES)];
+        /* The difference in offsets is the size of the block */
+        int  cmpBytes = offsets[currentBlock + 1] - offsets[currentBlock];
+        {
+            const size_t read = read_bin(inpFp, cmpBuf, (size_t)cmpBytes);
+            if(read != (size_t)cmpBytes) { exit(4); }
+        }
+
+        /* Load the dictionary */
+        LZ4_setStreamDecode(lz4StreamDecode, dict, dictSize);
+        {
+            const int decBytes = LZ4_decompress_safe_continue(
+                lz4StreamDecode, cmpBuf, decBuf, cmpBytes, BLOCK_BYTES);
+            if(decBytes <= 0) { exit(5); }
+            {
+                /* Write out the part of the data we care about */
+                int blockLength = MIN(length, (decBytes - offset));
+                write_bin(outFp, decBuf + offset, (size_t)blockLength);
+                offset = 0;
+                length -= blockLength;
+            }
+        }
+    }
+}
+
+
+int compare(FILE* fp0, FILE* fp1, int length)
+{
+    int result = 0;
+
+    while(0 == result) {
+        char b0[4096];
+        char b1[4096];
+        const size_t r0 = read_bin(fp0, b0, MIN(length, (int)sizeof(b0)));
+        const size_t r1 = read_bin(fp1, b1, MIN(length, (int)sizeof(b1)));
+
+        result = (int) r0 - (int) r1;
+
+        if(0 == r0 || 0 == r1) {
+            break;
+        }
+        if(0 == result) {
+            result = memcmp(b0, b1, r0);
+        }
+        length -= r0;
+    }
+
+    return result;
+}
+
+
+int main(int argc, char* argv[])
+{
+    char inpFilename[256] = { 0 };
+    char lz4Filename[256] = { 0 };
+    char decFilename[256] = { 0 };
+    char dictFilename[256] = { 0 };
+    int offset;
+    int length;
+    char dict[DICTIONARY_BYTES];
+    int dictSize;
+
+    if(argc < 5) {
+        printf("Usage: %s input dictionary offset length", argv[0]);
+        return 0;
+    }
+
+    snprintf(inpFilename, 256, "%s", argv[1]);
+    snprintf(lz4Filename, 256, "%s.lz4s-%d", argv[1], BLOCK_BYTES);
+    snprintf(decFilename, 256, "%s.lz4s-%d.dec", argv[1], BLOCK_BYTES);
+    snprintf(dictFilename, 256, "%s", argv[2]);
+    offset = atoi(argv[3]);
+    length = atoi(argv[4]);
+
+    printf("inp    = [%s]\n", inpFilename);
+    printf("lz4    = [%s]\n", lz4Filename);
+    printf("dec    = [%s]\n", decFilename);
+    printf("dict   = [%s]\n", dictFilename);
+    printf("offset = [%d]\n", offset);
+    printf("length = [%d]\n", length);
+
+    /* Load dictionary */
+    {
+        FILE* dictFp = fopen(dictFilename, "rb");
+        dictSize = (int)read_bin(dictFp, dict, DICTIONARY_BYTES);
+        fclose(dictFp);
+    }
+
+    /* compress */
+    {
+        FILE* inpFp = fopen(inpFilename, "rb");
+        FILE* outFp = fopen(lz4Filename, "wb");
+
+        printf("compress : %s -> %s\n", inpFilename, lz4Filename);
+        test_compress(outFp, inpFp, dict, dictSize);
+        printf("compress : done\n");
+
+        fclose(outFp);
+        fclose(inpFp);
+    }
+
+    /* decompress */
+    {
+        FILE* inpFp = fopen(lz4Filename, "rb");
+        FILE* outFp = fopen(decFilename, "wb");
+
+        printf("decompress : %s -> %s\n", lz4Filename, decFilename);
+        test_decompress(outFp, inpFp, dict, DICTIONARY_BYTES, offset, length);
+        printf("decompress : done\n");
+
+        fclose(outFp);
+        fclose(inpFp);
+    }
+
+    /* verify */
+    {
+        FILE* inpFp = fopen(inpFilename, "rb");
+        FILE* decFp = fopen(decFilename, "rb");
+        seek_bin(inpFp, offset, SEEK_SET);
+
+        printf("verify : %s <-> %s\n", inpFilename, decFilename);
+        const int cmp = compare(inpFp, decFp, length);
+        if(0 == cmp) {
+            printf("verify : OK\n");
+        } else {
+            printf("verify : NG\n");
+        }
+
+        fclose(decFp);
+        fclose(inpFp);
+    }
+
+    return 0;
+}