Android NDK之使用 arm-v7a 汇编实现两数之和

技术分享 2年前 (2024-04-07) 0 999+

Android NDK之使用 arm-v7a 汇编实现两数之和

关键词： NDK armv7a WebRTC arm汇编 CMake

最近适配对讲程序，在webrtc的库编译的过程中，发现其为arm的平台定制了汇编程序以优化平方根倒数算法速度，上次写汇编还是8086的，借此机会初步尝试下android上arm汇编

具体jni工程建立就不介绍了，Android Studio直接可以从模板创建

工程目录如下

kryo@WSL1:/mnt/k/Android/NDK-Project/XXX/src/main$ tree  . ├── AndroidManifest.xml ├── cpp │   ├── asm │   │   ├── CMakeLists.txt │   │   ├── asm_defines.h │   │   ├── asm_jni.cpp │   │   ├── asm_jni.h │   │   ├── tow_sum_armv7a.S │   │   └── tow_sum_cpp.cpp └── java     └── com         └── kryo             ├── asm             │   └── TowSumAsm.java             └── ...

1、C++接口编写

asm_jni.h

#ifndef TOW_SUM_AMS_TEST_H #define TOW_SUM_AMS_TEST_H  #include <jni.h>  #ifdef USE_ASM     extern "C" int32_t     tow_sum_asm(int32_t *data_in, int32_t *data_out, int32_t data_len, int32_t ret_len, int32_t target); #else     extern "C" int32_t     tow_sum_cpp(int32_t *data_in, int32_t *data_out, int32_t data_len, int32_t target); #endif  #endif //TOW_SUM_AMS_TEST_H

这里分别使用asm和c代码各自实现一个暴搜版本的两数之和接口。关于asm传递5个参数是有用意的，涉及到函数调用约定，armv7a前4个参数用寄存器传参，超过4个的用栈传递

2、汇编实现

写汇编时我习惯先参考C代码去推导

tow_sum_cpp.cpp

#include "asm_jni.h"  extern "C" int32_t tow_sum_cpp(int32_t *data_in, int32_t *data_out, int32_t data_len,int32_t target) {     for (int i = 0; i < data_len; ++i) {         for (int j = i + 1; j < data_len; ++j) {             if (data_in[i] + data_in[j] == target) {                 data_out[0] = i;                 data_out[1] = j;                 return 0;             }         }     }     data_out[0] = 0;     data_out[1] = 0;     return -1; }

以下是具体汇编代码的实现，基本每行都给出了注释

tow_sum_armv7a.S

@ Input:( @        int32_t* data_in, -> r0 &data_in @        int32_t* data_out,-> r1 &data_out @        int32_t  data_len, -> r2 @        int32_t  ret_len, -> r3 @        int32_t target -> [sp]) @ Output: r0 32 bit unsigned integer @ @ r4: i-index @ r5: j-index @ r6: target @ r7: num1-buff @ r8: num2-buff @ r9: sum cache   #include "asm_defines.h"  GLOBAL_FUNCTION tow_sum .align  4 DEFINE_FUNCTION tow_sum     push {r4-r11} 		@ 保存现场      ldr r6, [sp, #32] 	@ 保存了8个寄存器，偏移8*4bytes取得第5个参数      mov r4, #0 			@ 初始化第一个数的索引 i     mov r5, #0 			@ 初始化第二个数的索引 j   LOOP_1:     sub r9, r2, #1 		@ 数组长度-1     cmp r4, r9			@ 判断i是否数组最后一个     beq FAL				@ 是就查找失败     mov r5, r4  		@ j = i  LOOP_2:     add r5, r5, #1 		@ j ++     lsl r9, r4, #2		@ 把索引 i 乘4得到地址偏移量     ldr r7, [r0, r9]	@ r7 = data_in[i],寄存器相对寻址, r0为 data_in的地址，加上偏移量取的数组元素     lsl r9, r5, #2     ldr r8, [r0, r9]	@ 同上得到 r8 = data_in[j]     add r9, r8, r7		@ 两数之和     cmp r9, r6			@ 与目标做比较     beq SUC				@ 成功     add r9, r5, #1		@ 没有成功     cmp r9, r2			@ if j < data_len     bne LOOP_2			@ then：下一轮j的查找     add r4, r4, #1		@ else: j没找到，把i++     b LOOP_1			@ 下一轮 i的查找  SUC:     str r4, [r1]		@ data_out[0] = i     str r5, [r1, #4]	@ data_out[1] = j     mov r0, #0			@ return 0     b END  FAL:     mov r4, #0     mov r5, #0     mov r0, #-1			@ return -1     b SUC  END:     pop {r4-r11}		@ 还原现场     bx  lr

3、JNI实现

asm_jni.cpp

#include "asm_jni.h" #include <android/log.h>  #define TAG "ASM_TEST"  #define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, TAG, __VA_ARGS__)  #ifdef __cplusplus extern "C" { #endif JNIEXPORT jintArray JNICALL     Java_com_kryo_asm_TowSumAsm_towsum(JNIEnv *env, jobject thiz, jintArray data, jint target) {          jintArray r_array = env->NewIntArray(2);         jint *elements_out = env->GetIntArrayElements(r_array, NULL);          jsize length = env->GetArrayLength(data);         jint *elements_in = env->GetIntArrayElements(data, NULL);      #ifdef USE_ASM         LOGD("call tow_sum_asm !n");         tow_sum_asm(elements_in, elements_out, (size_t) length, 2, (size_t) target);     #else         LOGD("call tow_sum_cpp !n");         tow_sum_cpp(elements_in, elements_out, (size_t) length, (size_t) target);     #endif          env->ReleaseIntArrayElements(data, elements_in, 0);         env->ReleaseIntArrayElements(r_array, elements_out, 0);          return r_array;     } #ifdef __cplusplus } #endif

TowSumAsm.java

public class TowSumAsm {     static {         System.loadLibrary("asm");     }     public native int[] towsum(int[] data, int target); }

最后贴一下从webrtc开源代码中copy来的`asm_defines.h`

/*  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.  *  *  Use of this source code is governed by a BSD-style license  *  that can be found in the LICENSE file in the root of the source  *  tree. An additional intellectual property rights grant can be found  *  in the file PATENTS.  All contributing project authors may  *  be found in the AUTHORS file in the root of the source tree.  */  #ifndef KRYO_INCLUDE_ASM_DEFINES_H_ #define KRYO_INCLUDE_ASM_DEFINES_H_  #if defined(__linux__) && defined(__ELF__) .section .note.GNU-stack,"",%progbits #endif  // Define the macros used in ARM assembly code, so that for Mac or iOS builds // we add leading underscores for the function names. #ifdef __APPLE__ .macro GLOBAL_FUNCTION name .global _name .private_extern _name .endm .macro DEFINE_FUNCTION name _name: .endm .macro CALL_FUNCTION name bl _name .endm .macro GLOBAL_LABEL name .global _name .private_extern _name .endm #else .macro GLOBAL_FUNCTION name .global name .hidden name .endm .macro DEFINE_FUNCTION name #if defined(__linux__) && defined(__ELF__) .type name,%function #endif name: .endm .macro CALL_FUNCTION name bl name .endm .macro GLOBAL_LABEL name .global name .hidden name .endm #endif  // With Apple's clang compiler, for instructions ldrb, strh, etc., // the condition code is after the width specifier. Here we define // only the ones that are actually used in the assembly files. #if (defined __llvm__) && (defined __APPLE__) .macro streqh reg1, reg2, num strheq reg1, reg2, num .endm #endif .text #endif  // KRYO_INCLUDE_ASM_DEFINES_H_

4、CMakeLists.txt编写生成libasm.so

CMakeLists.txt

cmake_minimum_required(VERSION 3.10.2)  project("asm")  ENABLE_LANGUAGE(ASM) #启用汇编支持  if(${ANDROID_ABI} STREQUAL "armeabi-v7a")     add_library(asm SHARED             asm_jni.cpp             tow_sum_armv7a.S)     add_definitions(-DUSE_ASM) elseif(${ANDROID_ABI} STREQUAL "arm64-v8a")     add_library(asm SHARED             asm_jni.cpp             tow_sum_cpp.cpp) else()     message(FATAL_ERROR "Unsupported ABI: ${ANDROID_ABI}") endif()  target_link_libraries(asm         log)

5、运行测试

TowSumAsm towSumAsm = new TowSumAsm(); int[] result = towSumAsm.towsum(new int[]{1, 3, 5, 7, 9}, 12); Log.d(TAG, "result " + result[0] + " " + result[1]);

2024-04-05 10:24:29.269 19863-19863 ASM_TEST                com.kryo.demo                        D  call tow_sum_asm ! 2024-04-05 10:24:29.269 19863-19863 JNI_Activity            com.kryo.demo                        D  result 1 4