Java是2+;比C快几倍(作为C+;+;)的子集)
下面的代码是一个非常低效的乘法算法。它是为了测试而写的。我相信我用不同的语言编写了相同的代码 下面是运行代码的结果Java是2+;比C快几倍(作为C+;+;)的子集),java,c++,c,performance,optimization,Java,C++,C,Performance,Optimization,下面的代码是一个非常低效的乘法算法。它是为了测试而写的。我相信我用不同的语言编写了相同的代码 下面是运行代码的结果 OS: Windows 7 language: C (as a subset of C++) compiler: Visual C++ optimization option: /Ox /Oi /Ot /Oy /GL running time (seconds): 40 +/- 1 compiler: MinGW/gcc optimization option: -O3 mar
OS: Windows 7
language: C (as a subset of C++)
compiler: Visual C++
optimization option: /Ox /Oi /Ot /Oy /GL
running time (seconds): 40 +/- 1
compiler: MinGW/gcc
optimization option: -O3 march=native
running time (seconds): 81 +/- 1
compiler: MinGW/g++
optimization option: -O3 march=native
running time (seconds): 82 +/- 1
language: Java
compiler: Oracle JDK
VM: Oracle JVM
running time (seconds): 18 +/- 1
我相信我在我的C代码中做了一些可怕的事情,完全优化的编译器无法以任何方式进行优化。如果有什么大问题,请告诉我。我正在计划一个项目,其中有一部分涉及大量的计算。我决定用C语言编写这个核心计算部分,但有了这样的结果,我宁愿用Java编写所有的东西;它更容易,甚至更快?我仍然相信C,所以如果我的代码中有任何问题,请告诉我。我所期望的是Java版本应该慢1.5倍或更慢,但不知何故它比C
测试c
#包括
#包括
#包括
#包括
typedef有符号字符字节;
typedef结构数组
{
字节*数据;
内伦;
}
阵列;
无效新数组(数组*a,整数len)
{
a->data=(字节*)malloc(len*sizeof(字节));
a->len=len;
}
void del_数组(数组*a)
{
免费(a->数据);
}
类型定义结构
{
数组数;
内伦;
}
BUI[1];
作废新建筑(建筑b、常量字符*s)
{
int len=strlen(s);
b->len=len;
新的数组(&b->num,len);
对于(int i=0;inum.data[i]=s[len-i-1]-'0';
}
}
德鲁街无效(b街)
{
del_数组(&b->num);
}
内部建筑cmp(建筑a、建筑b)
{
如果(a->len>b->len)
{
返回1;
}
如果(a->lenlen)
{
返回-1;
}
对于(int i=a->len-1;i>=0;--i)
{
如果(a->num.data[i]>b->num.data[i])
{
返回1;
}
如果(a->num.data[i]num.data[i])
{
返回-1;
}
}
返回0;
}
#定义最大值(A,B)(A>B?A:B)
无效建筑添加(建筑、建筑a、建筑b)
{
数组c;
新的_数组(&c,MAX(a->len,b->len)+1);
memset(c.data,0,c.len);
memcpy(c.data,a->num.data,a->len);
对于(int i=0;ilen;++i)
{
c、 数据[i]+=b->num.data[i];
}
对于(int i=0;i=10)
{
c、 数据[i+1]+=c.data[i]/10;
c、 数据[i]=10;
}
}
del_数组(&r->num);
r->num=c;
r->len=c.len;
对于(int i=r->num.len-1;r->num.data[i--]==0;--r->len);
}
无效建筑(建筑、建筑a、建筑b)
{
别克;
新_BUI(c,“0”);
{
别克一号;
新(一,一);;
别伊;
新_BUI(i,“0”);
对于(;BUI_cmp(i,a)<0;BUI_add(i,i,1))
{
添加(c、c、b);
}
德鲁比(一);
德鲁比(一);
}
del_数组(&r->num);
r->num=c->num;
r->len=c->len;
}
无效的BUI_打印(BUI b)
{
对于(inti=b->len-1;i>=0;--i)
{
putchar(b->num.data[i]+'0');
}
}
内部主(空)
{
布伊阿;
新(a,123456789);;
b区;
新(b,987654321);;
BUI_print(a);
FPUT(“x”,标准件);
布尤印刷(b);
FPUT(“=”,标准输出);
开始时间=时钟();
布伊穆尔(a、a、b);
时间=时钟();
BUI_print(a);
德鲁比(a);
德鲁比(b);
printf(“\n延迟时间:%.3f\n”,(双精度)(结束时间-开始时间)/每秒时钟数);
printf(“%d%d\n”,a->num.len,a->len);
返回0;
}
Test.java
import java.util.*;
BUI级
{
字节[]num;
内伦;
BUI(字符串s)
{
len=s.长度();
num=新字节[len];
对于(int i=0;ib.len)
{
返回1;
}
if(len=0;--i)
{
if(num[i]>b.num[i])
{
返回1;
}
if(num[i]=10)
{
c[i+1]+=c[i]/10;
c[i]=10;
}
}
num=c;
len=c.长度;
for(int i=num.length-1;num[i-->==0;--len);
}
无效mul(建筑a、建筑b)
{
BUI c=新的BUI(“0”);
{
BUI one=新的BUI(“1”);
BUI i=新的BUI(“0”);
对于(;i.cmp(a)<0;i.add(i,1))
{
c、 添加(c,b);
}
}
num=c.num;
len=c.len;
}
作废打印()
{
对于(int i=len-1;i>=0;--i)
{
系统输出打印(num[i]);
}
}
}
公开课考试
{
公共静态void main(字符串[]args)
{
BUI a=新的BUI(“123456789”);
BUI b=新的BUI(“987654321”);
a、 打印();
系统输出打印(“x”);
b、 打印();
系统输出打印(“=”);
长启动时间=System.currentTimeMillis();
a、 mul(a,b);
long end_time=System.currentTimeMillis();
a、 打印();
System.out.printf(“\n失效时间:%.3f\n”,(结束时间-开始时间)/1000.0);
}
}
“语言:C(作为C++的子集)”
只是没有
C不是C++的子集。它们有共同的语法(大多数是C),但大多数运行时检查是不同的(取决于编译器),解释代码的方式是不同的(在少数情况下)和大多数代码
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
typedef signed char byte;
typedef struct _Array
{
byte *data;
int len;
}
Array;
void new_Array(Array *a, int len)
{
a->data = (byte *)malloc(len * sizeof(byte));
a->len = len;
}
void del_Array(Array *a)
{
free(a->data);
}
typedef struct _BUI
{
Array num;
int len;
}
BUI[1];
void new_BUI(BUI b, const char *s)
{
int len = strlen(s);
b->len = len;
new_Array(&b->num, len);
for (int i = 0; i < len; ++i)
{
b->num.data[i] = s[len - i - 1] - '0';
}
}
void del_BUI(BUI b)
{
del_Array(&b->num);
}
int BUI_cmp(const BUI a, const BUI b)
{
if (a->len > b->len)
{
return 1;
}
if (a->len < b->len)
{
return -1;
}
for (int i = a->len - 1; i >= 0; --i)
{
if (a->num.data[i] > b->num.data[i])
{
return 1;
}
if (a->num.data[i] < b->num.data[i])
{
return -1;
}
}
return 0;
}
#define MAX(A, B) (A > B ? A : B)
void BUI_add(BUI r, const BUI a, const BUI b)
{
Array c;
new_Array(&c, MAX(a->len, b->len) + 1);
memset(c.data, 0, c.len);
memcpy(c.data, a->num.data, a->len);
for (int i = 0; i < b->len; ++i)
{
c.data[i] += b->num.data[i];
}
for (int i = 0; i < c.len - 1; ++i)
{
if (c.data[i] >= 10)
{
c.data[i + 1] += c.data[i] / 10;
c.data[i] %= 10;
}
}
del_Array(&r->num);
r->num = c;
r->len = c.len;
for (int i = r->num.len - 1; r->num.data[i--] == 0; --r->len);
}
void BUI_mul(BUI r, const BUI a, const BUI b)
{
BUI c;
new_BUI(c, "0");
{
BUI one;
new_BUI(one, "1");
BUI i;
new_BUI(i, "0");
for (; BUI_cmp(i, a) < 0; BUI_add(i, i, one))
{
BUI_add(c, c, b);
}
del_BUI(one);
del_BUI(i);
}
del_Array(&r->num);
r->num = c->num;
r->len = c->len;
}
void BUI_print(BUI b)
{
for (int i = b->len - 1; i >= 0; --i)
{
putchar(b->num.data[i] + '0');
}
}
int main(void)
{
BUI a;
new_BUI(a, "123456789");
BUI b;
new_BUI(b, "987654321");
BUI_print(a);
fputs(" x ", stdout);
BUI_print(b);
fputs(" = ", stdout);
time_t start_time = clock();
BUI_mul(a, a, b);
time_t end_time = clock();
BUI_print(a);
del_BUI(a);
del_BUI(b);
printf("\nelapsed time: %.3f\n", (double)(end_time - start_time) / CLOCKS_PER_SEC);
printf("%d %d\n", a->num.len, a->len);
return 0;
}
import java.util.*;
class BUI
{
byte[] num;
int len;
BUI(String s)
{
len = s.length();
num = new byte[len];
for (int i = 0; i < len; ++i)
{
num[i] = (byte)Character.getNumericValue(s.charAt(len - i - 1));
}
}
int cmp(BUI b)
{
if (len > b.len)
{
return 1;
}
if (len < b.len)
{
return -1;
}
for (int i = len - 1; i >= 0; --i)
{
if (num[i] > b.num[i])
{
return 1;
}
if (num[i] < b.num[i])
{
return -1;
}
}
return 0;
}
void add(BUI a, BUI b)
{
byte[] c = new byte[Math.max(a.len, b.len) + 1];
Arrays.fill(c, (byte)0);
System.arraycopy(a.num, 0, c, 0, a.num.length);
for (int i = 0; i < b.len; ++i)
{
c[i] += b.num[i];
}
for (int i = 0; i < c.length - 1; ++i)
{
if (c[i] >= 10)
{
c[i + 1] += c[i] / 10;
c[i] %= 10;
}
}
num = c;
len = c.length;
for (int i = num.length - 1; num[i--] == 0; --len);
}
void mul(BUI a, BUI b)
{
BUI c = new BUI("0");
{
BUI one = new BUI("1");
BUI i = new BUI("0");
for (; i.cmp(a) < 0; i.add(i, one))
{
c.add(c, b);
}
}
num = c.num;
len = c.len;
}
void print()
{
for (int i = len - 1; i >= 0; --i)
{
System.out.print(num[i]);
}
}
}
public class Test
{
public static void main(String[] args)
{
BUI a = new BUI("123456789");
BUI b = new BUI("987654321");
a.print();
System.out.print(" x ");
b.print();
System.out.print(" = ");
long start_time = System.currentTimeMillis();
a.mul(a, b);
long end_time = System.currentTimeMillis();
a.print();
System.out.printf("\nelapsed time: %.3f\n", (end_time - start_time) / 1000.0);
}
}
for (; BUI_cmp(i, a) < 0; BUI_inc(i))
{
BUI_addinplace(c, b);
}
void BUI_addinplace(BUI a, const BUI b) //a += b
{
int maxSize = MAX(a->len, b->len) + 1;
if (a->num.len < maxSize)
{
Array tmp;
new_Array(&tmp, maxSize);
memset(tmp.data, 0, tmp.len);
memcpy(tmp.data, a->num.data, a->len);
del_Array(&a->num);
a->num = tmp;
}
for (int i = 0; i < b->len; ++i)
{
a->num.data[i] += b->num.data[i];
}
int maxLen = a->len;
for (int i = 0; i < a->len; ++i)
{
if (a->num.data[i] >= 10)
{
a->num.data[i + 1] += a->num.data[i] / 10;
a->num.data[i] %= 10;
maxLen = i + 2;
}
}
if (maxLen > a->len) a->len = maxLen;
}
void BUI_inc(BUI a) //a += 1
{
int maxSize = a->len + 1;
if (a->num.len < maxSize)
{
++numAllocations;
Array tmp;
new_Array(&tmp, maxSize);
memset(tmp.data, 0, tmp.len);
memcpy(tmp.data, a->num.data, a->len);
del_Array(&a->num);
a->num = tmp;
}
++a->num.data[0];
if (a->num.data[0] < 10) return;
int maxLen = a->len;
for (int i = 0; i < a->len; ++i)
{
if (a->num.data[i] >= 10)
{
a->num.data[i + 1] += a->num.data[i] / 10;
a->num.data[i] %= 10;
maxLen = i + 2;
}
else {
break;
}
}
if (maxLen > a->len) a->len = maxLen;
}
#define BUFFER_SIZE 1048576 //reserve 1MB, although we only use 417bytes
typedef struct mem_block_hdr
{
unsigned short size; //size of the memory block, excluding header
char free; //is this block free
char cont; //not used
}mem_block_hdr_t;
struct _myallocdata
{
char mem[BUFFER_SIZE];
unsigned int highest_header_pos;
} my_alloc_data;
void init_block_hdr(void *mem)
{
mem_block_hdr_t *head = (mem_block_hdr_t*) mem;
head->size = USHRT_MAX;
head->free = 1;
head->cont = 0;
}
void init_my_alloc()
{
init_block_hdr(my_alloc_data.mem);
my_alloc_data.highest_header_pos = 0;
}
mem_block_hdr_t *next_header(mem_block_hdr_t *curr)
{
return (mem_block_hdr_t*) ((char*) curr + sizeof(mem_block_hdr_t) + curr->size);
}
mem_block_hdr_t *find_next_free(unsigned int size)
{
void * ret;
char end_reached = 0;
mem_block_hdr_t *head = (mem_block_hdr_t*) my_alloc_data.mem;
while(
(!head->free || head->size < size) &&
((char*) head - my_alloc_data.mem ) < my_alloc_data.highest_header_pos
)
{
head = next_header(head);
}
return head;
}
void *my_alloc(unsigned int size)
{
mem_block_hdr_t *header = find_next_free(size);
unsigned int diff = (char*) header - my_alloc_data.mem ;
if (header->size == USHRT_MAX)
{
header->size = size;
}
header->free = 0;
if (diff >= my_alloc_data.highest_header_pos)
{
mem_block_hdr_t *new_high = next_header(header);
init_block_hdr(new_high);
my_alloc_data.highest_header_pos = ((char*) new_high) - my_alloc_data.mem;
}
return (void *)++header;
}
void my_free(void *mem)
{
mem_block_hdr_t *hdr =(mem_block_hdr_t *) ((char *)mem - sizeof(mem_block_hdr_t));
hdr->free = 1;
}
void new_Array(Array *a, int len)
{
//a->data = (byte *) malloc(len * sizeof(byte));
a->data = (byte *) my_alloc(len * sizeof(byte));
a->len = len;
}
void del_Array(Array *a)
{
//free(a->data);
my_free(a->data);
}
//calling init_my_alloc() in main before using it
123456789 x 987654321 = 121932631112635269
elapsed time (custom alloc): 25.546
19 18
123456789 x 987654321 = 121932631112635269
elapsed time (malloc): 290.118
19 18
123456789 x 987654321 = 121932631112635269
elapsed time (custom alloc): 30.703
19 18
123456789 x 987654321 = 121932631112635269
elapsed time (malloc): 46.406
19 18