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refactored simple_buffer.c example (#363)

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This commit is contained in:
Yann Collet 2017-06-08 12:51:56 -07:00
parent 7e15e240ab
commit 775e63ee01
3 changed files with 50 additions and 43 deletions
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1
examples/.gitignore vendored
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@ -6,4 +6,5 @@
/ringBufferHC /ringBufferHC
/lineCompress /lineCompress
/frameCompress /frameCompress
/simpleBuffer
/*.exe /*.exe

11
examples/Makefile
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@ -27,9 +27,10 @@
# kindly provided by Takayuki Matsuoka # kindly provided by Takayuki Matsuoka
# ########################################################################## # ##########################################################################
CFLAGS ?= -O3 CPPFLAGS += -I../lib
CFLAGS += -std=gnu99 -Wall -Wextra -Wundef -Wshadow -Wcast-align -Wstrict-prototypes CFLAGS ?= -O3
FLAGS := -I../lib $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) CFLAGS += -std=gnu99 -Wall -Wextra -Wundef -Wshadow -Wcast-align -Wstrict-prototypes
FLAGS := $(CPPFLAGS) $(CFLAGS) $(LDFLAGS)
TESTFILE= Makefile TESTFILE= Makefile
LZ4DIR := ../lib LZ4DIR := ../lib
@ -48,7 +49,8 @@ endif
default: all default: all
all: printVersion doubleBuffer dictionaryRandomAccess ringBuffer ringBufferHC lineCompress frameCompress all: printVersion doubleBuffer dictionaryRandomAccess ringBuffer ringBufferHC \
lineCompress frameCompress simpleBuffer
printVersion: $(LZ4DIR)/lz4.c printVersion.c printVersion: $(LZ4DIR)/lz4.c printVersion.c
$(CC) $(FLAGS) $^ -o $@$(EXT) $(CC) $(FLAGS) $^ -o $@$(EXT)
@ -85,6 +87,7 @@ test : all
./ringBufferHC$(EXT) $(TESTFILE) ./ringBufferHC$(EXT) $(TESTFILE)
./lineCompress$(EXT) $(TESTFILE) ./lineCompress$(EXT) $(TESTFILE)
./frameCompress$(EXT) $(TESTFILE) ./frameCompress$(EXT) $(TESTFILE)
./simpleBuffer$(EXT)
$(LZ4) -vt $(TESTFILE).lz4 $(LZ4) -vt $(TESTFILE).lz4
clean: clean:

81
examples/simple_buffer.c
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@ -8,10 +8,10 @@
*/ */
/* Includes, for Power! */ /* Includes, for Power! */
#include "lz4.h" // This is all that is required to expose the prototypes for basic compression and decompression. #include "lz4.h" // This is all that is required to expose the prototypes for basic compression and decompression.
#include <stdio.h> // For printf() #include <stdio.h> // For printf()
#include <string.h> // For memcmp() #include <string.h> // For memcmp()
#include <stdlib.h> // For exit() #include <stdlib.h> // For exit()
/* /*
* Easy show-error-and-bail function. * Easy show-error-and-bail function.
@ -28,37 +28,39 @@ void run_screaming(const char *message, const int code) {
*/ */
int main(void) { int main(void) {
/* Introduction */ /* Introduction */
// Below we will have a Compression and Decompression section to demonstrate. There are a few important notes before we start: // Below we will have a Compression and Decompression section to demonstrate.
// 1) The return codes of LZ4_ functions are important. Read lz4.h if you're unsure what a given code means. // There are a few important notes before we start:
// 2) LZ4 uses char* pointers in all LZ4_ functions. This is baked into the API and probably not going to change. If your // 1) The return codes of LZ4_ functions are important.
// program uses pointers that are unsigned char*, void*, or otherwise different you may need to do some casting or set the // Read lz4.h if you're unsure what a given code means.
// right -W compiler flags to ignore those warnings (e.g.: -Wno-pointer-sign). // 2) LZ4 uses char* pointers in all LZ4_ functions.
// This is baked into the API and probably not going to change.
// If your program uses pointers that are unsigned char*, void*, or otherwise different,
// you may need to do some casting or set the right -W compiler flags to ignore those warnings (e.g.: -Wno-pointer-sign).
/* Compression */ /* Compression */
// We'll store some text into a variable pointed to by *src to be compressed later. // We'll store some text into a variable pointed to by *src to be compressed later.
const char *src = "Lorem ipsum dolor sit amet, consectetur adipiscing elit."; const char* const src = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
// The compression function needs to know how many bytes of exist. Since we're using a string, we can use strlen() + 1 (for \0). // The compression function needs to know how many bytes exist. Since we're using a string, we can use strlen() + 1 (for \0).
const size_t src_size = strlen(src) + 1; const int src_size = (int)(strlen(src) + 1);
// LZ4 provides a function that will tell you the maximum size of compressed output based on input data via LZ4_compressBound(). // LZ4 provides a function that will tell you the maximum size of compressed output based on input data via LZ4_compressBound().
const size_t max_dst_size = LZ4_compressBound(src_size); const int max_dst_size = LZ4_compressBound(src_size);
// We will use that size for our destination boundary when allocating space. // We will use that size for our destination boundary when allocating space.
char *compressed_data = malloc(max_dst_size); char* compressed_data = malloc(max_dst_size);
if (compressed_data == NULL) if (compressed_data == NULL)
run_screaming("Failed to allocate memory for *compressed_data.", 1); run_screaming("Failed to allocate memory for *compressed_data.", 1);
// That's all the information and preparation LZ4 needs to compress *src into *compressed_data. Invoke LZ4_compress_default now // That's all the information and preparation LZ4 needs to compress *src into *compressed_data.
// with our size values and pointers to our memory locations. Save the return value for error checking. // Invoke LZ4_compress_default now with our size values and pointers to our memory locations.
int return_value = 0; // Save the return value for error checking.
return_value = LZ4_compress_default(src, compressed_data, src_size, max_dst_size); const int compressed_data_size = LZ4_compress_default(src, compressed_data, src_size, max_dst_size);
// Check return_value to determine what happened. // Check return_value to determine what happened.
if (return_value < 0) if (compressed_data_size < 0)
run_screaming("A negative result from LZ4_compress_default indicates a failure trying to compress the data. See exit code (echo $?) for value returned.", return_value); run_screaming("A negative result from LZ4_compress_default indicates a failure trying to compress the data. See exit code (echo $?) for value returned.", compressed_data_size);
if (return_value == 0) if (compressed_data_size == 0)
run_screaming("A result of 0 means compression worked, but was stopped because the destination buffer couldn't hold all the information.", 1); run_screaming("A result of 0 means compression worked, but was stopped because the destination buffer couldn't hold all the information.", 1);
if (return_value > 0) if (compressed_data_size > 0)
printf("We successfully compressed some data!\n"); printf("We successfully compressed some data!\n");
// Not only does a positive return_value mean success, the value returned == the number of bytes required. You can use this to // Not only does a positive return_value mean success, the value returned == the number of bytes required.
// realloc() *compress_data to free up memory, if desired. We'll do so just to demonstrate the concept. // You can use this to realloc() *compress_data to free up memory, if desired. We'll do so just to demonstrate the concept.
const size_t compressed_data_size = return_value;
compressed_data = (char *)realloc(compressed_data, compressed_data_size); compressed_data = (char *)realloc(compressed_data, compressed_data_size);
if (compressed_data == NULL) if (compressed_data == NULL)
run_screaming("Failed to re-alloc memory for compressed_data. Sad :(", 1); run_screaming("Failed to re-alloc memory for compressed_data. Sad :(", 1);
@ -66,25 +68,26 @@ int main(void) {
/* Decompression */ /* Decompression */
// Now that we've successfully compressed the information from *src to *compressed_data, let's do the opposite! We'll create a // Now that we've successfully compressed the information from *src to *compressed_data, let's do the opposite! We'll create a
// *new_src location of size src_size since we know that value. // *new_src location of size src_size since we know that value.
char *new_src = malloc(src_size); char* const regen_buffer = malloc(src_size);
if (new_src == NULL) if (regen_buffer == NULL)
run_screaming("Failed to allocate memory for *new_src.", 1); run_screaming("Failed to allocate memory for *regen_buffer.", 1);
// The LZ4_decompress_safe function needs to know where the compressed data is, how many bytes long it is, where the new_src // The LZ4_decompress_safe function needs to know where the compressed data is, how many bytes long it is,
// memory location is, and how large the new_src (uncompressed) output will be. Again, save the return_value. // where the regen_buffer memory location is, and how large regen_buffer (uncompressed) output will be.
return_value = LZ4_decompress_safe(compressed_data, new_src, compressed_data_size, src_size); // Again, save the return_value.
if (return_value < 0) const int decompressed_size = LZ4_decompress_safe(compressed_data, regen_buffer, compressed_data_size, src_size);
run_screaming("A negative result from LZ4_decompress_fast indicates a failure trying to decompress the data. See exit code (echo $?) for value returned.", return_value); if (decompressed_size < 0)
if (return_value == 0) run_screaming("A negative result from LZ4_decompress_safe indicates a failure trying to decompress the data. See exit code (echo $?) for value returned.", decompressed_size);
if (decompressed_size == 0)
run_screaming("I'm not sure this function can ever return 0. Documentation in lz4.h doesn't indicate so.", 1); run_screaming("I'm not sure this function can ever return 0. Documentation in lz4.h doesn't indicate so.", 1);
if (return_value > 0) if (decompressed_size > 0)
printf("We successfully decompressed some data!\n"); printf("We successfully decompressed some data!\n");
// Not only does a positive return value mean success, the value returned == the number of bytes read from the compressed_data // Not only does a positive return value mean success,
// stream. I'm not sure there's ever a time you'll need to know this in most cases... // value returned == number of bytes regenerated from compressed_data stream.
/* Validation */ /* Validation */
// We should be able to compare our original *src with our *new_src and be byte-for-byte identical. // We should be able to compare our original *src with our *new_src and be byte-for-byte identical.
if (memcmp(src, new_src, src_size) != 0) if (memcmp(src, regen_buffer, src_size) != 0)
run_screaming("Validation failed. *src and *new_src are not identical.", 1); run_screaming("Validation failed. *src and *new_src are not identical.", 1);
printf("Validation done. The string we ended up with is:\n%s\n", new_src); printf("Validation done. The string we ended up with is:\n%s\n", regen_buffer);
return 0; return 0;
} }