LIBJPEG-TURBO库移植

一、libjpeg-turbo库下载

    libjpeg-turbo是libjpeg的升级版，性能有所提升

        libpng库链接：https://libpng.sourceforge.io/index.html

二、ubuntu上验证libjpeg-turbo

1. 编译libjpeg-turbo库，tar -zxvf libjpeg-turbo-2.1.3.tar.gz && cd libjpeg-turbo-2.1.3 && mkdir build && cd build && cmake .. && make，如下图

2. 修改djepg.c 

#include "jinclude.h"
#include "jpeglib.h"
#include <setjmp.h>

struct my_error_mgr {

	struct jpeg_error_mgr pub;  /* "public" fields */
	jmp_buf setjmp_buffer;    /* for return to caller */
	
};
 
typedef struct my_error_mgr * my_error_ptr;


static void my_error_exit (j_common_ptr cinfo)
{
	my_error_ptr myerr = (my_error_ptr) cinfo->err;
	
	(*cinfo->err->output_message) (cinfo);

	longjmp(myerr->setjmp_buffer, 1);

}


int main(int argc, char **argv)
{
    struct jpeg_decompress_struct cinfo;
    struct my_error_mgr jerr;
    FILE * infile;
    FILE * outfile;
    int row_stride;
    unsigned char *buffer;



	struct timeval start,end;
	gettimeofday(&start, NULL);

    if (argc != 3)
    {
        printf("Usage: \n");
        printf("%s <jpg_file> <output_file>\n", argv[0]);
        return -1;
    }

	// 指定源文件
	if ((infile = fopen(argv[1], "rb")) == NULL) {
	    fprintf(stderr, "can't open %s\n", argv[1]);
	    return -1;
	}

	if ((outfile = fopen(argv[2], "w")) == NULL) {
	    fprintf(stderr, "can't open %s\n", argv[1]);
	    return -1;
	}
	printf("size :%d\n",sizeof(struct jpeg_decompress_struct));

	//错误处理 回调函数	
	cinfo.err = jpeg_std_error(&jerr.pub);
	jerr.pub.error_exit = my_error_exit;
	if (setjmp(jerr.setjmp_buffer)) {
		printf("cinfo->err->msg_code :%d\n",cinfo.err->msg_code);
		jpeg_destroy_decompress(&cinfo);
		fclose(infile);
		fclose(outfile);
		return 0;
	}

    jpeg_create_decompress(&cinfo);
    jpeg_stdio_src(&cinfo, infile);

    // 用jpeg_read_header获得jpg信息
    jpeg_read_header(&cinfo, TRUE);
	
    /* 源信息 */
    printf("image_width = %d\n", cinfo.image_width);
    printf("image_height = %d\n", cinfo.image_height);
    printf("num_components = %d\n", cinfo.num_components);


    // 设置解压参数,比如放大、缩小

	cinfo.scale_num=1;
	cinfo.scale_denom=1;

    // 启动解压：jpeg_start_decompress   
    jpeg_start_decompress(&cinfo);

    /* 输出的图象的信息 */
    printf("output_width = %d\n", cinfo.output_width);
    printf("output_height = %d\n", cinfo.output_height);
    printf("output_components = %d\n", cinfo.output_components);//解压的是rgb，故为3元素

    // 一行的数据长度
    row_stride = cinfo.output_width * cinfo.output_components;
    buffer = malloc(row_stride);//分配空间用来存储一行数据

    // 循环调用jpeg_read_scanlines来一行一行地获得解压的数据
    while (cinfo.output_scanline < cinfo.output_height) 
    {
        (void) jpeg_read_scanlines(&cinfo, &buffer, 1);
		fwrite(buffer, row_stride, 1, outfile);

    }

	gettimeofday(&end, NULL);


	long timeuse = 1000000*(end.tv_sec - start.tv_sec) + end.tv_usec-start.tv_usec;
	printf("time =%ld\n", timeuse);

    free(buffer);
	fclose(infile);
	fclose(outfile);
    jpeg_finish_decompress(&cinfo);
    jpeg_destroy_decompress(&cinfo);

    return 0;
}

3.执行make，mkdir test && cp djpeg test && cd test && ./djpeg test.jpg test.rgb，效果如下

三、向其它平台移植

        适配不同交叉编译器，cd build && cmake -DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc .. ，其余步骤同上