android arm64硬件实现加速crc32算法

来源：互联网发布：c语言中bind函数编辑：程序博客网时间：2024/05/16 08:05

在android arm64平台下，crc32，aes等常用算法有指令集实现。故在android下，可借助这些指令实现代码加速。

如何判断自己的手机是否支持crc32呢？有三个方法:

方法1，直接查看/proc/cpuinfo

方法2，使用ELF辅助向量 API

unsigned long hwcap = getauxval(AT_HWCAP);if (hwcap & HWCAP_CRC32)      return 1;}return 0;

第三个方法：

使用cpu-features库

#include <cpu-features.h>uint64_t cap = android_getCpuFeatures();if (cap & ANDROID_CPU_ARM64_FEATURE_CRC32) {     return 1;}return 0;

这里只讨论使用第三种方法的实现，完整代码如下：

#ifdef __ANDROID__#ifdef __aarch64__#define CRC32X(crc, value) __asm__("crc32x %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))#define CRC32W(crc, value) __asm__("crc32w %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))#define CRC32H(crc, value) __asm__("crc32h %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))#define CRC32B(crc, value) __asm__("crc32b %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))#define CRC32CX(crc, value) __asm__("crc32cx %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))#define CRC32CW(crc, value) __asm__("crc32cw %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))#define CRC32CH(crc, value) __asm__("crc32ch %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))#define CRC32CB(crc, value) __asm__("crc32cb %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))uint32_t __arm64_accelerate_crc32(uint32_t crc, const void* chunk, size_t size) {uint64_t cap = android_getCpuFeatures();if (!(cap & ANDROID_CPU_ARM64_FEATURE_CRC32)) return 0;register uint32_t l = crc ^ 0xffffffffu; // 使用局部变量，利用寄存器优化register size_t len = size; // 同上const uint8_t* p = reinterpret_cast<const uint8_t *>(chunk);#define STEP1 do {\CRC32CB(l, *p++);\len--;\} while (0)#define STEP2 do {\CRC32CH(l, *(uint16_t *)p);        \p += 2;\len -= 2;\} while (0)#define STEP4 do {\CRC32CW(l, *(uint32_t *)p);        \p += 4;\len -= 4;\} while (0)#define STEP8 do {\CRC32CX(l, *(uint64_t *)p);        \p += 8;\len -= 8;\} while (0)// 512路循环内联展开while (len >= 512) {STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;}// 直接使用if判断，效果会高点if (len >= 256) {STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;}if (len >= 128) {STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;}if (len >= 64) {STEP8; STEP8; STEP8; STEP8;STEP8; STEP8; STEP8; STEP8;}if (len >= 32) {STEP8; STEP8; STEP8; STEP8;}if (len >= 16) {STEP8; STEP8;}if (len >= 8) {STEP8;}if (len >= 4) {STEP4;}if (len >= 2) {STEP2;}if (len >= 1) {STEP1;}#undef STEP8#undef STEP4#undef STEP2#undef STEP1return ~l;}

注意，crc32x系列与crc32cx系列，这是被乘的多项式不同

其中crc32x 系列的多项式系数是: 0x4C11DB7,而crc32cx系列的多项式系数是0x1EDC6F41

使用clock计算CPU的时间测试如下：

测试机器为Android 5.0，nubia，测试数据为200字节的随意字符串

阅读全文

0 0