android 编译libjpeg
之前需要将yuv转换为jpg图像，查看网上说libjpeg-turbo比libjpeg快2-3倍，但是在android手机上实践了一下，需要40-60个ms，这个虽然比以前的300ms好多了，但是还是不能满足我的要求，进一步查看了网上信息，libjpeg-turbo是为x86和x86-64进行优化的使用了SIMD指令，而手机上不支持，所以需要在试验一下libjpeg的需要。下面是我的编译步骤：
1、先到官网上下载源码http://www.ijg.org/files/jpegsr9.zip 最新的是jpegsr9
2、然后加压，生成jpeg-9,进入并创建jni目录，将里面的内容都拷贝到jni里面
3、生成配置文件，在jni目录下面创建config.sh文件，然后在里面添加：
NDK=/opt/android-ndk-r8d PLATFORM=$NDK/platforms/android-8/arch-arm/ PREBUILT=$NDK/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86 CC=$PREBUILT/bin/arm-linux-androideabi-gcc ./configure --prefix=/home/jpeg-9/jni/dist --host=arm CC="$CC --sysroot=$PLATFORM"4、然后改变config.sh的权限，并执行,得到配置文件：
chmod 775 config.sh sh config.sh
5、生成Android.mk文件，内容如下：
LOCAL_PATH := $(my-dir)
include $(CLEAR_VARS)
# From autoconf-generated Makefile
LOCAL_MODULE := libjpeg
LOCAL_ARM_MODE=arm
LOCAL_SRC_FILES := \
jaricom.c \
jcapimin.c \
jcapistd.c \
jcarith.c \
jccoefct.c \
jccolor.c \
jcdctmgr.c \
jchuff.c \
jcinit.c \
jcmainct.c \
jcmarker.c \
jcmaster.c \
jcomapi.c \
jcparam.c \
jcprepct.c \
jcsample.c \
jctrans.c \
jdapimin.c \
jdapistd.c \
jdarith.c \
jdatadst.c \
jdatasrc.c \
jdcoefct.c \
jdcolor.c \
jddctmgr.c \
jdhuff.c \
jdinput.c \
jdmainct.c \
jdmarker.c \
jdmaster.c \
jdmerge.c \
jdpostct.c \
jdsample.c \
jdtrans.c \
jerror.c \
jfdctflt.c \
jfdctfst.c \
jfdctint.c \
jidctflt.c \
jidctfst.c \
jidctint.c \
jquant1.c \
jquant2.c \
jutils.c \
jmemmgr.c \
jmemnobs.c
LOCAL_C_INCLUDES := $(LOCAL_PATH)
LOCAL_CFLAGS :=-O3 -fstrict-aliasing -fprefetch-loop-arrays -DANDROID \
-DANDROID_TILE_BASED_DECODE -DENABLE_ANDROID_NULL_CONVERT
include $(BUILD_SHARED_LIBRARY)
6、运行ndk-build,结果如下：
root@zhangjie:/home/jpeg-9/jni# ndk-build Compile arm : jpeg <= jaricom.c Compile arm : jpeg <= jcapimin.c Compile arm : jpeg <= jcapistd.c Compile arm : jpeg <= jcarith.c Compile arm : jpeg <= jccoefct.c Compile arm : jpeg <= jccolor.c Compile arm : jpeg <= jcdctmgr.c Compile arm : jpeg <= jchuff.c Compile arm : jpeg <= jcinit.c Compile arm : jpeg <= jcmainct.c Compile arm : jpeg <= jcmarker.c Compile arm : jpeg <= jcmaster.c Compile arm : jpeg <= jcomapi.c Compile arm : jpeg <= jcparam.c Compile arm : jpeg <= jcprepct.c Compile arm : jpeg <= jcsample.c Compile arm : jpeg <= jctrans.c Compile arm : jpeg <= jdapimin.c Compile arm : jpeg <= jdapistd.c Compile arm : jpeg <= jdarith.c Compile arm : jpeg <= jdatadst.c Compile arm : jpeg <= jdatasrc.c Compile arm : jpeg <= jdcoefct.c Compile arm : jpeg <= jdcolor.c Compile arm : jpeg <= jddctmgr.c Compile arm : jpeg <= jdhuff.c Compile arm : jpeg <= jdinput.c Compile arm : jpeg <= jdmainct.c Compile arm : jpeg <= jdmarker.c Compile arm : jpeg <= jdmaster.c Compile arm : jpeg <= jdmerge.c Compile arm : jpeg <= jdpostct.c Compile arm : jpeg <= jdsample.c Compile arm : jpeg <= jdtrans.c Compile arm : jpeg <= jerror.c Compile arm : jpeg <= jfdctflt.c Compile arm : jpeg <= jfdctfst.c Compile arm : jpeg <= jfdctint.c Compile arm : jpeg <= jidctflt.c Compile arm : jpeg <= jidctfst.c Compile arm : jpeg <= jidctint.c Compile arm : jpeg <= jquant1.c Compile arm : jpeg <= jquant2.c Compile arm : jpeg <= jutils.c Compile arm : jpeg <= jmemmgr.c Compile arm : jpeg <= jmemnobs.c SharedLibrary : libjpeg.so Install : libjpeg.so => libs/armeabi/libjpeg.so
7、由于我只想要编码所以精简了代码，将编译出的库只包含编码，不包含解码库，下面的代码如下，只需要替换Android.mk文件相同部分就可以：
LOCAL_SRC_FILES := jniffmpeg/AppDecodeH264.c \
jniffmpeg/yuv420rgb565.s \
jniffmpeg/yuv2jpg.c \
jpeg-9/jaricom.c \
jpeg-9/jcapimin.c \
jpeg-9/jcapistd.c \
jpeg-9/jcarith.c \
jpeg-9/jccoefct.c \
jpeg-9/jccolor.c \
jpeg-9/jcdctmgr.c \
jpeg-9/jchuff.c \
jpeg-9/jcinit.c \
jpeg-9/jcmainct.c \
jpeg-9/jcmarker.c \
jpeg-9/jcmaster.c \
jpeg-9/jcomapi.c \
jpeg-9/jcparam.c \
jpeg-9/jcprepct.c \
jpeg-9/jcsample.c \
jpeg-9/jctrans.c \
jpeg-9/jdatadst.c \
jpeg-9/jerror.c \
jpeg-9/jfdctflt.c \
jpeg-9/jfdctfst.c \
jpeg-9/jfdctint.c \
jpeg-9/jidctflt.c \
jpeg-9/jidctfst.c \
jpeg-9/jidctint.c \
jpeg-9/jquant1.c \
jpeg-9/jquant2.c \
jpeg-9/jutils.c \
jpeg-9/jmemmgr.c \
jpeg-9/jmemnobs.c