一、第一种方法：
1.修改helloneon.c 中代码
a.将
char* str;
改为
char str[512] = {0};
b.将
asprintf(&str, "FIR Filter benchmark:\nC version : %g ms\n", time_c);
改为
sprintf(str, "FIR Filter benchmark:\nC version : %g ms\n", time_c);
同时删除 free(str);
（b 项 有两处都要修改）
c.将
return (*env)->NewStringUTF(env, buffer);
改为
return env->NewStringUTF(buffer);
2.将helloneon.c改名为helloneon.cpp
将helloneon-intrinsics.c改名为helloneon-intrinsics.cpp
3.将Android.mk中
将
LOCAL_SRC_FILES := helloneon.c
改为
LOCAL_SRC_FILES := helloneon.cpp
将
LOCAL_SRC_FILES += helloneon-intrinsics.c.neon
改为
LOCAL_SRC_FILES += helloneon-intrinsics.cpp.neon
4.打开 helloneon.cpp
在#include 和 各种 #define 后面添加：
#ifdef __cplusplus
extern "C" {
#endif
在代码段最后面添加：
#ifdef __cplusplus
}
#endif
不修改这一条的话，会提示找不到stringFromJNI。
不明问题：
1.经常提示一些jni和cpu-features的函数未定义。在路径中添加jni.h和cpu-features.h
2.即便是添加了arm_neon.h，还是会提示：
Type 'int16x4_t' could not be resolved helloneon-intrinsics.cpp /HelloNeon/jni line 35
但是 重启eclipse 一般就不提示了。一旦打开了helloneon-intrinsics.cpp还是会提示。
最终 hello-neon.cpp
1 /* 2 * Copyright (C) 2010 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 * 16 */ 17 #include <jni.h> 18 #include <time.h> 19 #include <stdio.h> 20 #include <stdlib.h> 21 #include <cpu-features.h> 22 #include "helloneon-intrinsics.h" 23 24 #define DEBUG 0 25 26 #if DEBUG 27 #include <android/log.h> 28 # define D(x...) __android_log_print(ANDROID_LOG_INFO,"helloneon",x) 29 #else 30 # define D(...) do {} while (0) 31 #endif 32 33 #ifdef __cplusplus 34 extern "C" { 35 #endif 36 37 /* return current time in milliseconds */ 38 static double 39 now_ms(void) 40 { 41 struct timespec res; 42 clock_gettime(CLOCK_REALTIME, &res); 43 return 1000.0*res.tv_sec + (double)res.tv_nsec/1e6; 44 } 45 46 47 /* this is a FIR filter implemented in C */ 48 static void 49 fir_filter_c(short *output, const short* input, const short* kernel, int width, int kernelSize) 50 { 51 int offset = -kernelSize/2; 52 int nn; 53 for (nn = 0; nn < width; nn++) { 54 int sum = 0; 55 int mm; 56 for (mm = 0; mm < kernelSize; mm++) { 57 sum += kernel[mm]*input[nn+offset+mm]; 58 } 59 output[nn] = (short)((sum + 0x8000) >> 16); 60 } 61 } 62 63 #define FIR_KERNEL_SIZE 32 64 #define FIR_OUTPUT_SIZE 2560 65 #define FIR_INPUT_SIZE (FIR_OUTPUT_SIZE + FIR_KERNEL_SIZE) 66 #define FIR_ITERATIONS 600 67 68 static const short fir_kernel[FIR_KERNEL_SIZE] = { 69 0x10, 0x20, 0x40, 0x70, 0x8c, 0xa2, 0xce, 0xf0, 0xe9, 0xce, 0xa2, 0x8c, 070, 0x40, 0x20, 0x10, 70 0x10, 0x20, 0x40, 0x70, 0x8c, 0xa2, 0xce, 0xf0, 0xe9, 0xce, 0xa2, 0x8c, 070, 0x40, 0x20, 0x10 }; 71 72 static short fir_output[FIR_OUTPUT_SIZE]; 73 static short fir_input_0[FIR_INPUT_SIZE]; 74 static const short* fir_input = fir_input_0 + (FIR_KERNEL_SIZE/2); 75 static short fir_output_expected[FIR_OUTPUT_SIZE]; 76 77 /* This is a trivial JNI example where we use a native method 78 * to return a new VM String. See the corresponding Java source 79 * file located at: 80 * 81 * apps/samples/hello-neon/project/src/com/example/neon/HelloNeon.java 82 */ 83 jstring 84 Java_com_example_neon_HelloNeon_stringFromJNI( JNIEnv* env, 85 jobject thiz ) 86 { 87 //char* str; 88 char str[512] = {0}; 89 uint64_t features; 90 char buffer[512]; 91 char tryNeon = 0; 92 double t0, t1, time_c, time_neon; 93 94 /* setup FIR input - whatever */ 95 { 96 int nn; 97 for (nn = 0; nn < FIR_INPUT_SIZE; nn++) { 98 fir_input_0[nn] = (5*nn) & 255; 99 } 100 fir_filter_c(fir_output_expected, fir_input, fir_kernel, FIR_OUTPUT_SIZE, FIR_KERNEL_SIZE); 101 } 102 103 /* Benchmark small FIR filter loop - C version */ 104 t0 = now_ms(); 105 { 106 int count = FIR_ITERATIONS; 107 for (; count > 0; count--) { 108 fir_filter_c(fir_output, fir_input, fir_kernel, FIR_OUTPUT_SIZE, FIR_KERNEL_SIZE); 109 } 110 } 111 t1 = now_ms(); 112 time_c = t1 - t0; 113 114 sprintf(str, "FIR Filter benchmark:\nC version : %g ms\n", time_c); 115 //asprintf(&str, "FIR Filter benchmark:\nC version : %g ms\n", time_c); 116 strlcpy(buffer, str, sizeof buffer); 117 118 //free(str); 119 120 strlcat(buffer, "Neon version : ", sizeof buffer); 121 122 if (android_getCpuFamily() != ANDROID_CPU_FAMILY_ARM) { 123 strlcat(buffer, "Not an ARM CPU !\n", sizeof buffer); 124 goto EXIT; 125 } 126 127 features = android_getCpuFeatures(); 128 if ((features & ANDROID_CPU_ARM_FEATURE_ARMv7) == 0) { 129 strlcat(buffer, "Not an ARMv7 CPU !\n", sizeof buffer); 130 goto EXIT; 131 } 132 133 /* HAVE_NEON is defined in Android.mk ! */ 134 #ifdef HAVE_NEON 135 if ((features & ANDROID_CPU_ARM_FEATURE_NEON) == 0) { 136 strlcat(buffer, "CPU doesn't support NEON !\n", sizeof buffer); 137 goto EXIT; 138 } 139 140 /* Benchmark small FIR filter loop - Neon version */ 141 t0 = now_ms(); 142 { 143 int count = FIR_ITERATIONS; 144 for (; count > 0; count--) { 145 fir_filter_neon_intrinsics(fir_output, fir_input, fir_kernel, FIR_OUTPUT_SIZE, FIR_KERNEL_SIZE); 146 } 147 } 148 t1 = now_ms(); 149 time_neon = t1 - t0; 150 sprintf(str, "%g ms (x%g faster)\n", time_neon, time_c / (time_neon < 1e-6 ? 1. : time_neon)); 151 //asprintf(&str, "%g ms (x%g faster)\n", time_neon, time_c / (time_neon < 1e-6 ? 1. : time_neon)); 152 strlcat(buffer, str, sizeof buffer); 153 //free(str); 154 155 /* check the result, just in case */ 156 { 157 int nn, fails = 0; 158 for (nn = 0; nn < FIR_OUTPUT_SIZE; nn++) { 159 if (fir_output[nn] != fir_output_expected[nn]) { 160 if (++fails < 16) 161 D("neon[%d] = %d expected %d", nn, fir_output[nn], fir_output_expected[nn]); 162 } 163 } 164 D("%d fails\n", fails); 165 } 166 #else /* !HAVE_NEON */ 167 strlcat(buffer, "Program not compiled with ARMv7 support !\n", sizeof buffer); 168 #endif /* !HAVE_NEON */ 169 EXIT: 170 //return (*env)->NewStringUTF(env, buffer); // C Version 171 return env->NewStringUTF(buffer); // C++ Version 172 } 173 174 #ifdef __cplusplus 175 } 176 #endif
二、第二种方法：
1. helloneon.cpp的修改如下
1 /* 2 * Copyright (C) 2010 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 * 16 */ 17 #include <jni.h> 18 #include <time.h> 19 #include <stdio.h> 20 #include <stdlib.h> 21 #include <cpu-features.h> 22 #include "helloneon-intrinsics.h" 23 24 #define DEBUG 0 25 26 #if DEBUG 27 #include <android/log.h> 28 # define D(x...) __android_log_print(ANDROID_LOG_INFO,"helloneon",x) 29 #else 30 # define D(...) do {} while (0) 31 #endif 32 33 #ifdef __cplusplus 34 extern "C" { 35 #endif 36 37 #define LOG_TAG "helloneon" 38 #define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__) 39 static JavaVM *gJVM; 40 static const char *classPathName = "com/example/neon/HelloNeon"; 41 42 /* return current time in milliseconds */ 43 static double 44 now_ms(void) 45 { 46 struct timespec res; 47 clock_gettime(CLOCK_REALTIME, &res); 48 return 1000.0*res.tv_sec + (double)res.tv_nsec/1e6; 49 } 50 51 52 /* this is a FIR filter implemented in C */ 53 static void 54 fir_filter_c(short *output, const short* input, const short* kernel, int width, int kernelSize) 55 { 56 int offset = -kernelSize/2; 57 int nn; 58 for (nn = 0; nn < width; nn++) { 59 int sum = 0; 60 int mm; 61 for (mm = 0; mm < kernelSize; mm++) { 62 sum += kernel[mm]*input[nn+offset+mm]; 63 } 64 output[nn] = (short)((sum + 0x8000) >> 16); 65 } 66 } 67 68 #define FIR_KERNEL_SIZE 32 69 #define FIR_OUTPUT_SIZE 2560 70 #define FIR_INPUT_SIZE (FIR_OUTPUT_SIZE + FIR_KERNEL_SIZE) 71 #define FIR_ITERATIONS 600 72 73 static const short fir_kernel[FIR_KERNEL_SIZE] = { 74 0x10, 0x20, 0x40, 0x70, 0x8c, 0xa2, 0xce, 0xf0, 0xe9, 0xce, 0xa2, 0x8c, 070, 0x40, 0x20, 0x10, 75 0x10, 0x20, 0x40, 0x70, 0x8c, 0xa2, 0xce, 0xf0, 0xe9, 0xce, 0xa2, 0x8c, 070, 0x40, 0x20, 0x10 }; 76 77 static short fir_output[FIR_OUTPUT_SIZE]; 78 static short fir_input_0[FIR_INPUT_SIZE]; 79 static const short* fir_input = fir_input_0 + (FIR_KERNEL_SIZE/2); 80 static short fir_output_expected[FIR_OUTPUT_SIZE]; 81 82 /* This is a trivial JNI example where we use a native method 83 * to return a new VM String. See the corresponding Java source 84 * file located at: 85 * 86 * apps/samples/hello-neon/project/src/com/example/neon/HelloNeon.java 87 */ 88 static jstring stringforneon( JNIEnv* env, jobject thiz ) 89 { 90 //char* str; 91 char str[512] = {0}; 92 uint64_t features; 93 char buffer[512]; 94 char tryNeon = 0; 95 double t0, t1, time_c, time_neon; 96 97 /* setup FIR input - whatever */ 98 { 99 int nn; 100 for (nn = 0; nn < FIR_INPUT_SIZE; nn++) { 101 fir_input_0[nn] = (5*nn) & 255; 102 } 103 fir_filter_c(fir_output_expected, fir_input, fir_kernel, FIR_OUTPUT_SIZE, FIR_KERNEL_SIZE); 104 } 105 106 /* Benchmark small FIR filter loop - C version */ 107 t0 = now_ms(); 108 { 109 int count = FIR_ITERATIONS; 110 for (; count > 0; count--) { 111 fir_filter_c(fir_output, fir_input, fir_kernel, FIR_OUTPUT_SIZE, FIR_KERNEL_SIZE); 112 } 113 } 114 t1 = now_ms(); 115 time_c = t1 - t0; 116 117 sprintf(str, "FIR Filter benchmark:\nC version : %g ms\n", time_c); 118 //asprintf(&str, "FIR Filter benchmark:\nC version : %g ms\n", time_c); 119 strlcpy(buffer, str, sizeof buffer); 120 121 //free(str); 122 123 strlcat(buffer, "Neon version : ", sizeof buffer); 124 125 if (android_getCpuFamily() != ANDROID_CPU_FAMILY_ARM) { 126 strlcat(buffer, "Not an ARM CPU !\n", sizeof buffer); 127 goto EXIT; 128 } 129 130 features = android_getCpuFeatures(); 131 if ((features & ANDROID_CPU_ARM_FEATURE_ARMv7) == 0) { 132 strlcat(buffer, "Not an ARMv7 CPU !\n", sizeof buffer); 133 goto EXIT; 134 } 135 136 /* HAVE_NEON is defined in Android.mk ! */ 137 #ifdef HAVE_NEON 138 if ((features & ANDROID_CPU_ARM_FEATURE_NEON) == 0) { 139 strlcat(buffer, "CPU doesn't support NEON !\n", sizeof buffer); 140 goto EXIT; 141 } 142 143 /* Benchmark small FIR filter loop - Neon version */ 144 t0 = now_ms(); 145 { 146 int count = FIR_ITERATIONS; 147 for (; count > 0; count--) { 148 fir_filter_neon_intrinsics(fir_output, fir_input, fir_kernel, FIR_OUTPUT_SIZE, FIR_KERNEL_SIZE); 149 } 150 } 151 t1 = now_ms(); 152 time_neon = t1 - t0; 153 sprintf(str, "%g ms (x%g faster)\n", time_neon, time_c / (time_neon < 1e-6 ? 1. : time_neon)); 154 //asprintf(&str, "%g ms (x%g faster)\n", time_neon, time_c / (time_neon < 1e-6 ? 1. : time_neon)); 155 strlcat(buffer, str, sizeof buffer); 156 //free(str); 157 158 /* check the result, just in case */ 159 { 160 int nn, fails = 0; 161 for (nn = 0; nn < FIR_OUTPUT_SIZE; nn++) { 162 if (fir_output[nn] != fir_output_expected[nn]) { 163 if (++fails < 16) 164 D("neon[%d] = %d expected %d", nn, fir_output[nn], fir_output_expected[nn]); 165 } 166 } 167 D("%d fails\n", fails); 168 } 169 #else /* !HAVE_NEON */ 170 strlcat(buffer, "Program not compiled with ARMv7 support !\n", sizeof buffer); 171 #endif /* !HAVE_NEON */ 172 EXIT: 173 //return (*env)->NewStringUTF(env, buffer); // C Version 174 return env->NewStringUTF(buffer); // C++ Version 175 } 176 177 static JNINativeMethod methods[] = { 178 {"stringFromJNI","()Ljava/lang/String;", (void*) stringforneon }, 179 }; 180 181 /* 182 * Register several native methods for one class. 183 */ 184 static int registerNativeMethods(JNIEnv* env, const char* className, 185 JNINativeMethod* gMethods, int numMethods) { 186 jclass clazz; 187 188 clazz = env->FindClass(className); 189 if (clazz == NULL) { 190 D(ANDROID_LOG_INFO, LOG_TAG, "clazz == NULL"); 191 return JNI_FALSE; 192 } 193 194 if (env->RegisterNatives(clazz, gMethods, numMethods) < 0) { 195 D(ANDROID_LOG_INFO, LOG_TAG, 196 "RegisterNatives failed for"); 197 //LOGE("RegisterNatives failed for '%s'", className); 198 return JNI_FALSE; 199 } 200 201 return JNI_TRUE; 202 } 203 204 /* 205 * Register native methods for all classes we know about. 206 * 207 * returns JNI_TRUE on success. 208 */ 209 static int registerNatives(JNIEnv* env) { 210 if (!registerNativeMethods(env, classPathName, methods, 211 sizeof(methods) / sizeof(methods[0]))) { 212 return JNI_FALSE; 213 } 214 215 return JNI_TRUE; 216 } 217 218 int jniThrowException(JNIEnv* env, const char* className, const char* msg) { 219 jclass exceptionClass = env->FindClass(className); 220 if (exceptionClass == NULL) 221 return -1; 222 223 if (env->ThrowNew(exceptionClass, msg) != JNI_OK) { 224 } 225 226 return 0; 227 } 228 JNIEnv* getJNIEnv() { 229 JNIEnv* env = NULL; 230 if (gJVM->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) 231 return NULL; 232 233 return env; 234 } 235 jint JNI_OnLoad(JavaVM* vm, void* reserved) { 236 JNIEnv* env = NULL; 237 jint result = -1; 238 gJVM = vm; 239 D(ANDROID_LOG_INFO, LOG_TAG, "JNI_OnLoad"); 240 if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) 241 return result; 242 243 if (registerNatives(env) != JNI_TRUE) 244 goto end; 245 246 result = JNI_VERSION_1_4; 247 248 end: 249 return result; 250 } 251 252 #ifdef __cplusplus 253 } 254 #endif
2.其他改动部分同方法一。
不明问题：
stringforneon 的返回类型 只能为 jstring 不能用 string。
参考
http://blog.csdn.net/martingang/article/details/8170940
如果提示错误：error: #error You must enable NEON instructions (e.g. -mfloat-abi=softfp -mfpu=neon) to use arm_neon.h
Android.mk 需要添加两句
1.LOCAL_SRC_FILES := helloneon.cpp 下面添加
TARGET_ARCH_ABI := armeabi-v7a
2.LOCAL_CFLAGS := -DHAVE_NEON=1 后边添加 -mfloat-abi=softfp -mfpu=neon -march=armv7-a
即是 LOCAL_CFLAGS := -DHAVE_NEON=1 -mfloat-abi=softfp -mfpu=neon -march=armv7-a