hi I m trying to convert my java code to c code for better speed ,
and I want to generate a random number in c code using jni(android)
in java code,
public int getRandomNumberFor()
{
Random random ;
random = new Random();
return random.nextInt(0xFF);
}
I don't know what code work for c
I tried finding example, but unfortunately I don't get it. can any one help me in this.?
Change your code as using C Programming in NDK :
#include <stdio.h>
#include <stdlib.h>
JNIEXPORT jint JNICALL Java_com_imrantestndk_androiddemo_NativeLib_Randomnum
(JNIEnv * env, jobject this){
int n;
n = rand()%100 + 1;
return n;
}
Or
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
JNIEXPORT jint JNICALL Java_com_imrantestndk_androiddemo_NativeLib_Randomnum
(JNIEnv * env, jobject this){
int random;
randomize();
random = random(100);
return random;
}
Related
I'm trying the use the OpenSSL Rand library with DRBG in an android app, this library is implemented in native code of NDK. At starting, the OpenSSL works fine but in many times the app crashed and don't show any throw message. Here is the only error message that showwing:
A/libc: Fatal signal 7 (SIGBUS), code 1 (BUS_ADRALN), fault addr 0xb1aedca6f2d64adf in tid 22101 (RenderThread), pid 22075 (android.example)
My code is the follow:
libnative.cpp
#include <jni.h>
#include <string>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <openssl/rand.h>
#include <openssl/rand_drbg.h>
#include <android/log.h>
#include <future>
#ifndef TAG
#define TAG "OpenSslApi"
#endif
#ifndef DEFAULT_VALUE_ERROR
#define DEFAULT_VALUE_ERROR 0
#endif
void thread_handler(union sigval sv) {}
extern "C"
JNIEXPORT void JNICALL
Java_com_android_random_OpenSslApi_initDrbgRandom(
JNIEnv * env,
jclass clazz) {
RAND_DRBG * randDrbgInstance = RAND_DRBG_new(NID_aes_256_ctr, RAND_DRBG_FLAG_CTR_NO_DF, nullptr);
RAND_DRBG_instantiate(randDrbgInstance, nullptr, 0);
RAND_DRBG_set_reseed_time_interval(randDrbgInstance, 0);
RAND_DRBG_set_reseed_interval(randDrbgInstance, 0);
}
std::pair < jint * , jint > generateRandomIntDrbg(jint * secureRandom, jint sizeKey) {
jint myStatus = RAND_DRBG_bytes(
RAND_DRBG_get0_public(),
(unsigned char * ) secureRandom,
sizeKey * sizeof(int)
);
return std::make_pair(secureRandom, myStatus);
}
extern "C"
JNIEXPORT jint JNICALL
Java_com_android_random_OpenSslApi_intDrbgGenerateSecureRandom(
JNIEnv * env,
jclass clazz,
jintArray empty_array,
jint size_key) {
struct sigevent sev {};
timer_t timerid;
memset( & sev, 0, sizeof(sev));
sev.sigev_notify = SIGEV_THREAD;
sev.sigev_notify_function = & thread_handler;
sev.sigev_value.sival_ptr = & timerid;
timer_create(CLOCK_MONOTONIC, & sev, & timerid);
JavaVM * javaVm = nullptr;
env -> GetJavaVM( & javaVm);
javaVm -> AttachCurrentThread( & env, (void ** ) & env);
jintArray array = env -> NewIntArray(size_key);
if (array == nullptr) {
return DEFAULT_VALUE_ERROR;
}
jint * secureRandomIntArray = env -> GetIntArrayElements(array, nullptr);
if (secureRandomIntArray == nullptr) {
return DEFAULT_VALUE_ERROR;
}
std::future < std::pair < jint * , jint >> futureIntRandom = std::async (generateRandomIntDrbg, secureRandomIntArray, size_key);
std::pair < jint * , jint > result = futureIntRandom.get();
jint * resultSecureRandom = std::get < jint * > (result);
if (resultSecureRandom == nullptr) {
return DEFAULT_VALUE_ERROR;
}
memcpy(secureRandomIntArray, empty_array, size_key);
env -> ReleaseIntArrayElements(empty_array, secureRandomIntArray, 0);
return std::get < jint > (result);
}
OpenSslApi.java
static {
System.loadLibrary("libnative");
}
public OpenSslApi() {
initDrbgRandom();
}
public static native void initDrbgRandom();
public static native int intDrbgGenerateSecureRandom(
int[] emptyArray,
final int sizeKey
);
Thanks for either suggestions about the solution of this error.
I have a C++ source file, and I want to call a method from my C++ file, but I dont know whats wrong.
Here is my cpp method:
static unsigned ALawEncode(uint8_t* dst, int16_t* src, size_t srcSize);
Here is where I would like to call my method:
#include <string.h>
#include <jni.h>
#include <stdint.h>
#include "G711.h"
extern "C" {
uint8_t* Java_com_example_qonclient_Codecs_encodeG711( JNIEnv* env, jobject thiz, int16_t* source ){
size_t size0 = sizeof(source);
G711 g711;
uint8_t *dst;
g711.ALawEncode(dst, source, size0);
return dst;
}
}
Could you help me?
I am studying OpenCV4Android SDK, in the 2.4.5 version, with the NDK framework, using which I can use native code (written in C/C++) in the Android environment. But I don't exactly understand how parameters are passed from Android to C.
For example, in the 'mixedprocessing' sample, in the directory 'jni' there's a .cpp file named 'jni_part', whose code is:
#include <jni.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <vector>
using namespace std;
using namespace cv;
extern "C" {
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_FindFeatures(JNIEnv*, jobject, jlong addrGray, jlong addrRgba);
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_FindFeatures(JNIEnv*, jobject, jlong addrGray, jlong addrRgba) {
Mat& mGr = *(Mat*)addrGray;
Mat& mRgb = *(Mat*)addrRgba;
vector<KeyPoint> v;
FastFeatureDetector detector(50);
detector.detect(mGr, v);
for( unsigned int i = 0; i < v.size(); i++ ) {
const KeyPoint& kp = v[i];
circle(mRgb, Point(kp.pt.x, kp.pt.y), 10, Scalar(255,0,0,255));
}
}
}
In the MainActivity there's the method:
public native void FindFeatures(long matAddrGr, long matAddrRgba);
So it's passed as parameter the native address of a Mat object, but how does it become a matrix in C?
And which features are detected from a FastFeatureDetector object?
FindFeatures, in Java, calls its exact equivalent in C/C++:
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_FindFeatures(JNIEnv*, jobject, jlong addrGray, jlong addrRgba){
Mat& mGr = *(Mat*)addrGray;
Mat& mRgb = *(Mat*)addrRgba;
...
This is where it becomes a cv::Mat. (Mat*) casts what is pointed by address addrGray (respectively addrRgba) to a "pointer to a cv::Mat". Then, the value pointed by this newly created pointer is put in mGr (respectively mRgb), which is a cv::Mat.
In other words, you only give to C/C++ an address in the memory, and you have to make sure that what's there actually is a valid cv::Mat.
About your second question, the FAST detector detects points of interest in the image (i.e. points that contain a lot of information). The idea is to be able to identify those points on multiple different images. To simplify, you can consider a feature detected by FAST as a corner in the image.
I was tring to use ORB feature in Android apps,and create a project.When I use BruteForceMatcher and write the code:dist=matches[i].distance, My IDE notice me that "Field 'distance' could not be resolved". Why this happened?
#include <jni.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/legacy/legacy.hpp>
#include <iostream>
#include <vector>
using namespace std;
using namespace cv;
extern "C" {
JNIEXPORT int JNICALL Java_org_opencv_samples_tutorial2_Tuturial2Activity_CompareFeatures(JNIEnv*, jobject, jlong addrGray, jlong addrRgba);
JNIEXPORT int JNICALL Java_org_opencv_samples_tutorial2_Tuturial2Activity_CompareFeatures(JNIEnv*, jobject, jlong addrGray, jlong addrRgba)
{
char img_filename1[]="/sdcard/src.jpg";
char img_filename2[]="/sdcard/demo.jpg";
Mat src1,src2;
src1=imread(img_filename1,CV_LOAD_IMAGE_GRAYSCALE);
src2=imread(img_filename2,CV_LOAD_IMAGE_GRAYSCALE);
ORB orb;
vector<KeyPoint> keys1,keys2;
Mat descriptors1,descriptors2;
orb(src1,Mat(),keys1,descriptors1);
orb(src2,Mat(),keys2,descriptors2);
BruteForceMatcher<HammingLUT> matcher;
vector<DMatch> matches;
matcher.match(descriptors1,descriptors2,matches);
double max_dist=0; double min_dist=255;
//--Quick calculation of max and min distances between keypoints
for (int i=0;i<descriptors1.rows;i++)
{
double dist=matches[i].distance;
}
return 0;
}
}
Goto Project Properties -> C/C++ General -> GNU C++ ->
Edit change 4.x to 4.4.3 in ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/4.x....
I have been messing with my own little project to teach myself the android ndk using c++ and jni but I can't figure out how to pass the data from a java float array to the c++ array. I have used the jni set up. Most the tutorials I find are either too simple and don't explain enough or are too complicated and go over my understanding at the moment. So, can some one just point me to a simple example of an array being passed from java to c++, then have some method/function performed on the data and sent back to java.
Heres my attempt so far but I have two errors left in the way. Im not sure if the rest of the syntax is up to par either but I don't see anything at compile time.
#include <iostream>
#include <Eigen/Dense>
#include <math.h>
#include <jni.h>
using namespace Eigen;
Vector3f vec;
Vector3f vec2;
Vector3f vecRtrn;
void vecLoad(float x, float y, float z, float x2, float y2, float z2){
vec(0) = x;
vec(1) = y;
vec(2) = z;
vec2(0) = x2;
vec2(1) = y2;
vec2(2) = z2;
}
void vecAdd(Vector3f vecA, Vector3f vecB){
vecRtrn = vecA+vecB;
}
extern "C"
{
JNIEXPORT jfloatArray JNICALL Java_jnimath_act_JnimathActivity_test
(JNIEnv *env, jobject obj, jfloatArray fltarray1, jfloatArray fltarray2){
float array1[3];
jfloatArray flt1 = fltarray1;
jfloatArray flt2 = fltarray2;
//flt1 = env->GetFloatArrayElements( fltarray1,0);
//flt2 = env->GetFloatArrayElements( fltarray2,0);
vecLoad(flt1[0], flt1[1], flt1[2], flt2[0], flt2[1], flt2[2]);
vecAdd(vec, vec2);
array1[0] = vecRtrn[0];
array1[1] = vecRtrn[1];
array1[2] = vecRtrn[2];
return array1;
};
}
And these are the errors at compile time
$ /cygdrive/c/android-ndk-r7/ndk-build
Compile++ thumb : test <= test.cpp
jni/test.cpp: In function '_jfloatArray* Java_jnimath_act_JnimathActivity_test(JNIEnv*, _jobject*, _jfloatArray*, _jfloatArray*)':
jni/test.cpp:42: error: cannot convert '_jfloatArray' to 'float' for argument '1' to 'void vecLoad(float, float, float, float, float, float)'
jni/test.cpp:49: error: cannot convert 'float*' to '_jfloatArray*' in return
make: *** [obj/local/armeabi/objs/test/test.o] Error 1
First you can't use jfloatArray directly. Instead, you should do this
JNIEXPORT jfloatArray JNICALL Java_jnimath_act_JnimathActivity_test
(JNIEnv *env, jobject obj, jfloatArray fltarray1, jfloatArray fltarray2)
{
jfloatArray result;
result = env->NewFloatArray(3);
if (result == NULL) {
return NULL; /* out of memory error thrown */
}
jfloat array1[3];
jfloat* flt1 = env->GetFloatArrayElements( fltarray1,0);
jfloat* flt2 = env->GetFloatArrayElements( fltarray2,0);
vecLoad(flt1[0], flt1[1], flt1[2], flt2[0], flt2[1], flt2[2]);
vecAdd(vec, vec2);
array1[0] = vecRtrn[0];
array1[1] = vecRtrn[1];
array1[2] = vecRtrn[2];
env->ReleaseFloatArrayElements(fltarray1, flt1, 0);
env->ReleaseFloatArrayElements(fltarray2, flt2, 0);
env->SetFloatArrayRegion(result, 0, 3, array1);
return result;
}
Please use this as a tutorial and study more. As I said before, studying will help you more than practicing at this time.
This is basically enough for create an empty array with new ndks. Assuming env is your jni environment.
jfloatArray jArray = env -> NewFloatArray(8);
validateAudio(JNIEnv* env, jobject obj, jstring resourceFolderPath, ,jfloatArray thresholdArray){
const char *resource_folder_path = (*env)->GetStringUTFChars(env,resourceFolderPath,0); // string parameter
const jfloat* threshold_array = (*env)->GetFloatArrayElements(env, thresholdArray,0); //float array
}
Instead the older style (above Tae-Sung Shin's code, still works), we should do this nowadays:
jfloatArray result;
result = (*env)->NewFloatArray( env, numbers_here );